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A HANDBOOK OF SOLAR ECLIPSES
The Solar Corona photographed at Yerbanis, Mexico, September 10, 1923, by the Sproul
Observatory Expedition of Swarthmore College, with camera of 65 feet focal length.
- -

A H A N D B O O. K. O. F
S O L A R E C L LP S E S
sº
*" BY
\ iſ ISABEL MARTIN LEWIS, A. M.
sº----
(Corrected with the N autical Almanac Office
of the U. S. Naval Observatory.)
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NEW YORK
DUFFIELD & COMPANY
1924,

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L 674
34o ser, 17-564
Copyright 1924 by
DUFFIELD & COMPANY
Printed in U.S.A.
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3. – 3 – 25
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LIST OF CHAPTERS
CHAPTER
PREFACE . . . . . . . . . . . . . . .
* I. THE GRANDEUR of A ToTAL SOLAR ECLIPSE
3% II. THE CAUSE OF ECLIPSES o
III. THE MOON'S SHADOW CONE AND THE PATH OF
TOTAL ECLIPSE &
IV. THE SARoS AND ECLIPSE SERIES
W. PAST AND PRESENT PREDICTIONS OF ECLIPSEs .
VI. How ECLIPSES ARE PREDICTED e
VII. Som ETHING FOR THE FLAT-EARTH THEORISTS
TO THINK ABOUT gº e º e º 'º
VIII. PAST TOTAL SOLAR ECLIPSES IN THE EASTERN
PART of THE UNITED STATES ſº º
IX. THE ToTAL Soi,AR ECLIPSE of JANUARY 24,
1925 © C C º
+ X. THE PARTIAL SOLAR ECLIPSE
XI. SHADow BANDs . . . . O
XII. BAILY's BEADS ſº e º 0
XIII. THE PASSING OF THE Moon's SHADow
XIV. THE CHROMOSPHERE AND THE FLASH SPEC-
TRUM . tº ſº tº e
XV. THE SOLAR PROMINENCES
* xvi. THE SOLAR CORONA
XVII. THE ECLIPSE PAINTING
XVIII. How To VIEw THE ECLIPSE
XIX. How THE ASTRONOMER OBSERVES AN ECLIPSE
XX. THE IMPORTANCE OF ECLIPSES
XXI. SomE NOTED ECLIPSES OF THE PAST ©-
XXII. Some ToTAL SOLAR ECLIPSES OF THE NEAR
FUTURE O
PAGE
3
10
15
19
25
32
36
48
53
59
61
64
68
73–
80
83
92
100
105
113
V
ILLUSTRATIONS
The Solar Corona photographed at Yerbanis, Mexico,
September 10, 1923, by the Sproul Observatory Ex-
pedition of Swarthmore College . . . . Frontispiece
Facing
Page
Chart showing Tracks of some Eclipses of the Present
Century, Past and Future . . . . . . . . . 26
Chart showing Path of Total Solar Eclipse of January
24, 1925, and also a table giving times and magni-
tude of the Eclipse for Principal Towns . . . . 38
The Solar Corona, photograph by Lick-Crocker Eclipse
Expedition, Wallal, Australia, September 21, 1922 . 55
Photograph of Prominences, Yerbanis, Mexico . . . 70
Heliosaurus Prominence photographed by Yerkes Ob-
servatory Expedition, 1918 Eclipse . . . . . . 72
Six views of Corona, showing change with the sunspot
cycle. (One Plate) . . . . . . . . . . . 76 .
The Corona of June 8, 1918, U. S. Naval Observatory
Expedition, Baker, Oregon . . . . . . . . . 81
View of Eclipse Camp, Swarthmore Expedition, Yer-
banis, Mexico, 1923, and Lick-Crocker Expedition,
Wallal, Australia, 1922 . . . . . . . . . . 96
Solar Prominences photographed at Mt. Wilson Ob-
servatory . . . . . . . . . . . . . . . 100
PREFACE
A total eclipse of the sun, an event of unusual interest and
rare occurrence in any one locality, is to take place in one of
the most densely populated parts of the United States,
mainly in Michigan, New York State, including New York
City, Connecticut and Rhode Island, on January 24, 1925.
Again a total eclipse of the sun is to occur in England on
June 29, 1927, the first to be visible in this country in two
centuries. Many decades will pass before another total
eclipse of the sun will be visible in either the northeastern
part of the United States or England. As much popular
interest will be aroused by the advent of these two eclipses
it occurred to the writer that something on the subject of
solar eclipses in general and these two eclipses in particular
might not be out of place at the present time.
The aim of this little book is to present in a non-technical
manner some of the chief facts concerning the cause and
prediction of eclipses and their historical and scientific im-
portance, as well as the manner in which they are observed,
scientifically and otherwise.
A special chapter has been devoted to the eclipse of Jan-
uary 24, 1925, and a considerable part of another chapter
to the eclipse of June 29, 1927, but the greater part of the
book deals with phenomena observable at any total eclipse
of the sun or with matter of a general nature regarding
eclipses so it is hoped that the usefulness of the book will not
end with the passing of these two eclipses into history.
The scientific importance of eclipses is great. Expeditions
ix
PREFACE
have been sent halfway around the world to observe total
eclipses of the sun.
Those who live in the north-eastern part of the United
States are now to have one delivered at their doors. A
number of expeditions will probably come to the path of
totality of the eclipse of next January and the general pub-
lic will be interested to know something of the nature of the
work undertaken by such expeditions. It is also possible
that the general observer of the eclipse who is located in or
close to the path of totality, may make observations of real
value to science during the eclipse. A few suggestions on how
to observe the eclipse scientifically will be found in chapters
dealing with phenomena observable at and near the time of
total eclipse.
The value of two modern inventions, the moving picture
camera and the aeroplane in connection with the scientific
observation of total eclipses of the sun is not to be overlooked
and it is to be hoped that they will both be brought to the
aid of the astronomer during the coming eclipse as they were
during the eclipse of September 10, 1923.
The writer wishes to take this opportunity to acknowledge
her indebtedness to those who have furnished photographs
or have otherwise aided in the preparation of this book.
The Superintendent of the U. S. Naval Observatory has
kindly permitted the use of a photograph of the solar corona
of the eclipse of June 8, 1918, obtained by the U. S. Naval
Observatory Expedition to Baker, Oregon, in advance of its
publication in the volume of eclipse observations now being
prepared for the press at this institution. The director of
the Nautical Almanac Office has also permitted the use of
data bearing on the eclipse of June 29, 1927, which will be
observable in England, Norway and Sweden and Siberia.
IX
PREFACE
Grateful acknowledgement is also made of the kindness of
Dr. John A. Miller, Director of the Sproul Observatory of
Swarthmore College, in furnishing photographs of the solar
corona and prominences and views of the eclipse camp and
instruments taken on the occasion of the eclipse of Septem-
ber 10, 1923, by the Sproul Observatory Expedition to Yer-
banis, Mexico.
Photographs of the solar corona of the eclipse of Septem-
ber 21, 1922, and views of the eclipse camp of the Lick-
Crocker Eclipse Expedition which observed this eclipse at
Wallal, Australia, were also kindly furnished by Dr. R. G.
Aitken, Associate Director of the Lick Observatory.
A photograph of the “Heliosaurus” or “Skeleton” prom-
inence, obtained by the Yerkes Observatory Eclipse Expedi-
tion to Matheson, Colorado, on the occasion of the total
eclipse of June 8, 1918, and the series of photographs of
different types of coronas shown in Plate VI were obtained
through the courtesy of Dr. E. B. Frost, Director of the
Yerkes Observatory and permission to use the photograph of
the solar prominence shown in Plate X, taken at Mount
Wilson without an eclipse, was obtained from Dr. W. S.
Adams, Director of the Mt. Wilson Observatory.
Mention should also be made of the excellent work done
by Mr. Alvin R. Meissner, Engraver, Washington, D. C., in
preparing an eclipse design for the cover from a preliminary
draft, and also the two charts, showing some eclipse tracks
of the present century and the path of the total eclipse of
January 24, 1925, respectively.
WASHINGTON, D. C.
July 14, 1924.
A HANDBOOK OF SOLAR ECLIPSEs
A HANDBOOK
OF SOLAR ECLIPSES
I
THE GRANDEUR OF A TOTAL SOLAR ECLIPSE
FROM time immemorial man has been strangely impressed by
the phenomenon of a total eclipse of the sun, which is the most
sublime and awe-inspiring sight that nature affords. Among
the early tribes and races of men the feeling excited by the
gradual blotting out of the sun was one of abject terror. To
many it was a sign of the wrath of the gods and all haste was
made to appease them. To others it was a portent of mis-
fortune in battle or the death of a ruler. In India and China,
it was the belief that the darkness of eclipse was caused by
a dragon with black claws who was attempting to devour the
sun and it was the chief duty of the astronomers of those
countries at time of eclipse to shoot arrows, beat gongs and
employ similar devices to frighten away this dragon with the
black claws.
In the middle ages the fear of eclipses seemed in no degree
abated for we read of men hiding in cellars during totality, of
women screaming and fainting and of the death by fright of
the timid Emperor Louis of Bavaria following a total eclipse
of the sun in the year A. D. 840 which had the more than
average duration of five minutes.
Even at the present time when the cause of eclipses is so
generally understood and keen scientific enthusiasm has dis-
placed the terror of past ages a hush of expectancy and a
3
4 A HANDBOOK OF SOLAR ECLIPSES
feeling almost of uneasiness settles over all as the slender
crescent of the disappearing sun rapidly narrows to the van-
ishing point. Man is then, more than at any other time,
brought into touch for a few fleeting moments with forces
over which he can have no control and the thought awes him
and brings with it an unconscious feeling of humility.
& Many live and die without
eVer beholdingº º, seen, however, it is a phenomenon
never to be forgotten. The black body of the moon standing
out, a huge globe, in sinister relief between sun and earth,
the sudden outflashing glory and radiance of the pearly corona
which can be seen at no other time, the scarlet prominences
rising from the surface of the hidden sun to heights of many
thousand miles, the unaccustomed presence of the brighter
stars and planets in the daytime, the darkness of twilight and
the unusual chill in the air, there is something in it all that
affects even the strongest nerves and it is almost with a sigh
of relief that we hail the return of the friendly sun.

II
THE CAUSE OF ECLIPSES
IF the earth, sun and moon were all in the same plane there
would be eclipses every month, an eclipse of the sun when
the moon passes between the sun and earth, and an eclipse of
the moon when the earth comes between sun and moon. As
it happens, however, the path, or orbit, in which the moon
travels around the earth is inclined to the plane in which the
earth is traveling around the sun. So, ordinarily, at the
time of new moon each month when the moon passes from
west to east of the sun it passes above or below the sun and
there is no eclipse of the sun. In the same way at full moon
it passes above or below the shadow of the earth and so
escapes eclipse itself. .
Twice a year, though, at intervals of six months, we find
that conditions are different. The moon is then at or near
one or the other of the two points in which its path intersects
the plane of the earth's orbit, called the nodes of the moon’s
orbit. If, at the time of new moon, the moon is within a
certain distance of the node, or crossing point, the three bodies
will be so nearly in a straight line that an eclipse of the sun
will occur, partial or total, depending upon how far the moon
is from its node. In like manner two weeks later at the time
of full moon, if the distance of the moon from the node has
not become too great in the interim, there will be an eclipse
of the moon when the moon will dip partially or wholly into
the shadow of the earth.

These periods separated by intervals of six months—eigh-
5
6 A HANDBOOK OF SOLAR ECLIPSES
teen days on either side of the node for the sun, eleven and a
half days on either side for the moon—during which eclipses
of sun and moon may occur are known as eclipse seasons. If
the nodes were fixed points it is evident that the eclipses would
always occur in the same months each year. As it happens,
however, the nodes are not stationary but are slowly shifting
westward at the rate of over eighteen degrees a year which
brings the eclipse season about twenty days earlier in each
successive year.
It can be shown from a study of the eclipse limits for the
sun and moon, which is too theoretical a matter to consider
here, that there must be each year at least two eclipses and
there may be as many as seven in exceptional instances.
When only two eclipses occur in a year they will both be
solar eclipses. There may be years in which no lunar eclipses
will occur but in every year there must be two solar eclipses
and there may be as many as five) This happened last in the
year 1823 and will happea—again in 1935. There can never
be in one year more than three eclipses of the moon.
In general the number of solar eclipses exceeds the number
of lunar eclipses three to two. Yet at any one point on the
earth’s surface there will be a total solar eclipse visible on an
average of once in about three and a half centuries while total
lunar eclipses will be seen every few years. This is because a
total Solar eclipse is visible only within a narrow strip about
five thousand miles in length and generally considerably less
than 150 miles in width, while a total eclipse of the moon is
visible over the entire hemisphere that is turned toward the
moon plus the part that will come into sight of the moon by
^ the turning of the earth on its axis during the eclipse.
III
THE MOON'S SHADOW-CONE AND THE PATH OF
- TOTAL ECLIPSE
THE shadow cast by a planet or its satellite into space is
coneshaped, as this is the form of shadow cast by a sphere
and these bodies are spheres. When this shadow-cone is in-
tercepted by another body in space one of two things will
happen depending upon the relative sizes and distances of the
two bodies. If the body upon which the shadow falls is
small compared to the body casting the shadow and at no
great distance from it, then it will pass into the shadow of
the larger body partly or completely and will be eclipsed.
This is what happens when the shadow of the earth strikes the
moon. As the diameter of the earth’s shadow at the distance
of the moon is about twice that of the moon itself the moon
may be completely emersed in the earth’s shadow for nearly
two hours. Also the four largest satellites of Jupiter are so
small compared with the huge shadow cast by this giant planet
of the solar system that they are continually passing into the
shadow of Jupiter for long periods. If, on the other hand,
the body casting the shadow is the smaller body, as when the
moon casts its shadow upon the earth, or one of the satellites
of Jupiter casts its shadow upou this huge planet, then an
observer looking down from space would see a small black dot
passing across the illuminated surface of the planet. This black
dot represents the intersection of the shadow-cone of the
smaller body with the surface of the larger body.
Many who have had an opportunity to look at Jupiter
7 -
8 A HANDBOOK OF SOLAR ECLIPSES
through the telescope have seen these shadows of the satellites
passing across the surface of the planet. This is also what
happens when our satellite the moon passes between earth
and Sun. The shadow-cone of the moon strikes the earth’s
surface and the shadow travels as a small circular dark spot
across the earth’s surface from west to east. The trail of this
black spot across the earth is the path of total solar eclipse and
anyone who is within it will see the sun totally eclipsed by
the moon. It is usually about five thousand miles long and
it cannot be more than about 170 miles in width. In Space
the shadow of the moon moves about 2100 miles an hour.
Put when it strikes the earth, on account of the turning of the
earth on its axis in the same direction in which the shadow
is moving, from west to east, the shadow has to overtake and
pass a moving point and so its motion with respect to the ob-
server is less than it is in free space. At the equator the ob-
server is moving at the rate of 1040 miles an hour but in 45°
north latitude he is moving only at the rate of 735 miles per
hour. So at the equator the moon’s shadow will pass the ob-
server at the rate of 2100-1040 or 1060 miles an hour, while
in 45° north or south latitude it will pass the observer at
the rate of 2100-735 or 1365 miles per hour. As the duration
of total eclipse at any point in the path depends upon how
long it takes this shadow to pass the observer it is evident that
the longest duration of total eclipse will be at the equator,
where the observer is being carried eastward by the earth's
rotation most rapidly. Under the most favorable combination
of circumstances which occur when the sun is farthest from
the earth and the moon nearest to the earth with the observer
at the equator and the eclipse occurring at noon the maximum
duration of a total eclipse of the sun is 7 minutes 58 seconds.
THE MOON'S SHADOW CONE 9
The average duration of a total solar eclipse, however, is
probably about three minutes.
Now the relative positions of the sun, moon and earth are
such that the vertex of the cone of the shadow may sometimes
fall short of the earth’s surface and in that case we have what
is known as an annular eclipse of the sun. That is, the moon
is not quite able to cover the disk of the sun and a small ring
or annulus of light is seen surrounding the dark disk of the
moon at time of greatest eclipse. The vertex of the shadow-
cone, it can be shown, may fall short of the earth’s surface
by as much as 20,000 miles and at the other extreme it may
extend about 18,000 miles beyond the earth's surface. Again
the vertex of the cone may just graze the surface of the earth
and the eclipse may even be annular at the ends and total in
the middle of its path. In this case the duration of totality
dwindles down to a second or so and the width of the shadow
path to practically zero. Outside of the path of total eclipse,
on either side of it to a distance of between 2000 and 3000
miles, the moon will partially cover the disk of the sun and a
partial solar eclipse will be visible. The magnitude of the
greatest obscuration of the sun by the moon for a point out-
side the path of total eclipse will depend upon the distance of
the observer from the path. The nearer the observer is to the
path of total eclipse the greater will be the maximum partial
eclipse. If the eclipse is total its magnitude is said to be
100 per cent., if half the diameter of the sun is covered by the
moon the magnitude is 50 per cent. At the outer limit of
the partial phase of the eclipse there will be a mere graze of
the disks of sun and moon with no eclipse visible to the eye.
IV
THE SAROS AND ECLIPSE SERIES
IT is a curious fact that after a definite interval of time an
eclipse, whether of sun or moon, will repeat itself, or ‘return,”
as we might say. Given sun, moon and earth in line at, or
close to, one of the nodes of the moon's orbit, a condition
which will result in an eclipse, of sun at new moon and of
moon at full moon,_then after a certain interval of time,
known as the eclipse Saros, which is 18 years, 10% days in
length, if five leap years intervene, and 18 years, 11/3 days if
four leap years intervene, there will be another eclipse at the
same node that will closely resemble the first one.
Though we do not wish to enter into the mathematics of
eclipse here, it may be said that this periodic recurrence of
eclipses in series follows from the fact that in this period
which is equal to about 6585% days there are exactly 223
lunations, or returns of new moon, 242 returns of the moon
to its node, and 19 returns of the sun to the same node. So
that at the end of the Saros period sun, moon and earth
will be in line again at the same node under practically the
same circumstances as before and another eclipse will be
bound to occur under nearly the same conditions as the
earlier eclipse. -
Considering now only solar eclipses, the chief difference be-
tween two eclipses separated by the Saros interval will be in
the location of the path of the moon's shadow on the earth's
surface. Since there is a fra lion of about one-third of a
10
THE MOON'S SHADOW CONE 11
day in the Saros and since in this third of a day the earth is
not standing still but turning in an eastward direction on its
axis the shadow of the moon will fall about one-third of a
revolution of 120 degrees in longitude westward of its previous
position. Compare for example the total solar eclipse of June
8, 1918 with the total solar eclipse of May 28, 1900. The
1918 eclipse was a return of the 1900 eclipse.
The duration of each eclipse was a little over two minutes
and the circumstances of the two eclipses were very similar.
Consider, however, the position of the middle of the path of
total eclipse for each one, where the eclipse occurred at local
noon. In the 1900 eclipse the position of this point was in
45° west longitude and 45° north latitude. In the 1918
eclipse it was in 151° west longitude and 51° north latitude,
a difference of 107° in longitude. This is about 120° west-
ward of the previous track as required by theory, the fraction
of the day being not exactly one-third and the other factors
affecting the position to some slight extent. If we wish to
find the next eclipse in this series we add 18 years eleven days
to the date of the 1918 eclipse and find that there will be an
eclipse on June 19, 1936. We can check the accuracy of our
prediction by referring to Oppolzer's Canon Der Finsternisse,
in which are given the approximate elements of the 8000 solar
and 5200 lunar eclipses that occur between the dates 1208
B. C. and 2162 A. D. with 160 charts that show the tracks of
all the principal total and annual eclipses. Here we find listed
a total solar eclipse of two and one-half minutes duration for
June 19, 1936 visible from Greece to Japan.
The word Saros, used to denote the interval between succes-
sive eclipses of the same series, means “repetition” and it is
believed that the Saros was first discovered and used by the
Chaldeans in predicting the occurrence of eclipses. It is cer-
12 A HANDBOOK OF SOLAR ECLIPSES
tain that the Chaldeans kept careful records of eclipses for
centuries and were the greatest astronomers of ancient times.
It is likely that Thales made use of the Saros in predicting his
famous eclipse of 585 B. C. which ended the battle between
the Lydians and the Medes. It was frequently made use of
later, by the Greeks and others and is, in fact, used at the
present time if a first rough approximation to the times of
future eclipses is desired.
A second most interesting feature of this periodic return
of eclipses in series arises from the fact that at each return
to the node the line of conjunction of sun, moon and earth
shifts westward about half a degree which in the case of solar
eclipses produces a change in the position of successive
eclipses of the series in latitude on the earth's surface. The
first eclipse in a series will occur when sun, moon and earth
are in line about 18°, or possibly somewhat less, to the east
of the node. The central line or axis of the moon’s shadow-
cone will then pass about two thousand miles or so above the
north pole of the earth or below the south pole depending
upon which of its two nodes the moon is near. In this case
the moon’s cone of shadow will not touch the surface of the
earth but there will be a small partial eclipse at and near
the pole. This is due to the fact that there is outside of the
true shadow-cone a sort of negative or penumbral cone as it
is called, to distinguish it from the true or umbral cone, which
has a diameter of about 4400 miles and within this penumbral
cone the sun is seen to be more or less partially obscured by
the moon. A series first enters then, at one of the poles of
the earth with the falling of a small part of the penumbral
shadow over the polar regions. At the next return, after the
Saros interval, there will be a little larger partial eclipse at
the pole but still the axis of the moon’s shadow-cone will be
SAROS AND ECLIPSE SERIES 13
off the earth. After about ten or eleven returns of the Saros
and a lapse of two hundred years the true shadow-cone will
strike the earth near the pole and there will be a path of total
or annular eclipse curving around or through the pole and a
little more than half of the penumbral shadow will also be on
the earth. Now for about seven and a half centuries there will
be at each return of the eclipse a path of total or annular
eclipse which is working gradually toward the other pole. The
series will be at its height when the track passes through
equatorial regions and when the penumbral shadow, which is
between four and five thousand miles wide, is entirely on the
earth.
After an interval of about 750 years the axis of the moon’s
shadow-cone will pass off the earth at the opposite pole and
then there will be for another two hundred years partial
solar eclipses near this pole of the earth, gradually decreasing
in size at each return of the eclipse until finally, after there
have been about ten partial eclipses, the penumbral shadow
will also leave the earth and the series will die out at the pole
opposite to the one at which it first appeared. The entire
series from the time of its first appearance at one pole to its
disappearance at the other lasts about 1150 years. In this
time there will be visible about 64 eclipses of which 43 or 44
will probably be total or annular, and the remainder partial
in polar regions.
As there are every year at least two solar eclipses while
there may, in rare cases, be as many as five, it is evident that
there are a number of eclipses series continually passing over
the earth’s surface year by year. There are new series starting
in at both poles and old series dying out and there are series
at their height with long tracks of total eclipse passing
over the equatorial regions where the duration is longest and
14 A HANDBOOK OF SOLAR ECLIPSES
the path widest. Some of these various eclipse tracks are
bound to intersect and one who lives at their point of inter.
section may see, if they are not many years apart in occur.
rence two total eclipses of the sun at short intervals, without
going away from home. This occurred for example in the
Yellowstone National Park where, within less than eleven
years, there were two total solar eclipses, one July 29, 1878 and
the other on January 1, 1889. At times certain portions of the
earth's surface will seem to be particularly favored by
eclipse tracks. In the middle ages Scotland seemed to get
more than its share of attention, five total eclipses occurring
in Edinburgh within a few centuries. Spain has been par-
ticularly favored in the past hundred years. Sumatra had a
fine total eclipse in 1901 most successfully observed by an ex-
pedition from the U. S. Naval Observatory and it will have
two more total solar eclipses in the immediate future, one on
January 14, 1926, and the other on May 9, 1929. On the
other hand London went over eight hundred years from A.
D. 878 to A. D. 1715 without a total solar eclipse and it has
had none since and is not likely to have one for another cen-
tury at least though on June 29, 1927 there will be a total
eclipse of short duration visible as near to London as Liver-
pool and a partial phase of 95 per cent. in London.
New York City, which so far in its history has never been
visited by a total solar eclipse, will find itself on the southern
limit of the path of total eclipse on January 24, 1925, with a
duration of total eclipse of half a minute.
V
PAST AND PRESENT PREDICTIONS OF ECLIPSES
IN early ages the accurate prediction of the circum-
stances of an eclipse of the sun was impossible. The Chal-
deans had, to be sure, discovered the Saros by means of which
the times of the occurrence of future eclipses could be pre-
dicted with a fair degree of accuracy. But to predict the
course that would be taken by the moon’s shadow over the
surface of the earth was quite another matter. This de-
pends not only on the positions of the sun and moon in the
heavens but also on the size and shape of the earth and the
motion of the observer with respect to the shadow, due to
the rotation of the earth, matters of which the early astrono-
mers knew next to nothing.
If it happened that an eclipse of the sun were total in the
afternoon at a certain point in Asia Minor or Greece, then at
its next return eighteen years later the path of the eclipse
would fall 120° to the westward in a part of the world that
was not even known to exist. At its third return, however,
the eclipse would fall in approximately the same longitude
as it did 54 years before but several hundred miles north or
south of its former position according to whether the series
to which it belonged was moving northward or southward.
By referring to past records of eclipses kept by the Chaldeans,
it might be possible to foretell in a rough way that a certain
eclipse of the sun would be total in some country or, possibly
even, some city of the then known world on a certain date.
It was probably through a knowledge of the Saros and from
15
16 A HANDBOOK OF SOLAR ECLIPSES
reference to such eclipse records that Thales was able to pre-
dict to the Ionians the eclipse which bears his name. This
is probably the most famous of all past eclipses occurring
as it did in the midst of a battle between the Lydians and the
Medes, who were so overcome with terror at the sight that they
ceased fighting and concluded a peace with was cemented with
a double marriage. Herodotus, the Greek historian, in writing
of this event states that Thales did predict even the year in
which the eclipse occurred. We imagine, though, that Thales
would not have been much of an astronomer even for that
period if he were not able with the aid of the Saros to predict
at least the day and even the approximate time of day when
the eclipse would take place.
To predict with the high degree of accuracy required today
the time and circumstances of eclipses of the sun, it is neces-
sary to have the most accurate positions that can possibly be
obtained of the sun and the moon, their parallaxes, or the
apparent angular dimensions of the earth as it would appear
at the distances of the two bodies, and an accurate knowledge
of the shape and size of the earth taking into account its
flattening at the poles and departure from a truly spherical
form. .
One of the most interesting and valuable books having to
do with the prediction of eclipses that has been published in
modern times is Oppolzer's Canon Der Finsternisse, which
is based upon modern tables of the positions of sun and moon
and which gives with considerable accuracy the astronomical
elements of all eclipses past and future between the years
1208 B. C. and 2162 A. D., 13,200 in number, 8000 of the sun
and 5,200 of the moon with 160 charts giving the approximate
position of the tracks of important total and annular eclipses
on the earth’s surface. This truly monumental work is of the
PAST AND PRESENT PREDICTIONS 17
highest value in fixing the chronological times of many im-
portant events in history that have been connected with the
occurrence of eclipses and in giving an approximate location
of the paths of future eclipses. As it was impossible to
undertake the computation of more than three points for each
curve, one at the center of the path giving the position of
the shadow at noon and one at either end corresponding to
sunrise and sunset, it was not always possible to obtain an
accurate curve to represent the eclipse track. In some cases
the paths have been found to be incorrectly placed in latitude
to the extent of one hundred miles or more. Also certain
errors in the lunar tables that were used introduced some addi-
tional small errors in the elements given and in the eclipse
tracks yet for the purpose for which it was intended, namely
to give a comprehensive survey of all series of eclipses as far
back as twelve hundred years before Christ, and for nearly
two hundred and fifty years to come, it has proved to be of
the greatest value.
For the benefit of astronomers and others who wish to make
scientific observations of eclipses and as a part of the routine
work connected with the publication of the American Ephe-
meris and Nautical Almanac predictions of all eclipses of the
sun and moon that occur each year are made by the Nautical
Almanac Office of the U. S. Naval Observatory at Washington,
D. C., a few years in advance. So we may say that the pre-
diction of eclipses has become one of the duties of the national
government and is no longer left to the option of individual
astronomers. It is well that this is so for the computation of
eclipses is an expensive and time-consuming piece of work
that would be a burden upon private observatories if they had
to undertake it.
As a result of an international agreement made in 1911
18 A HANDBOOK OF SOLAR ECLIPSES
at Paris by representatives of some of the leading countries
of the world, an exchange of astronomical computations be-
tween the Almanac Offices of these countries is now being
made to avoid unnecessary and expensive duplication of work.
Although each country, as before, publishes its own national
Almanac or Year-book giving the positions of the sun, moon,
planets, and stars and all important astronomical phenomena
for each year, much of the work is now contributed by the
astronomers of other countries in exchange for work of a sim-
ilar nature. Under this agreement the Nautical Almanac
Office at Washington now furnishes to England, France and
some other countries of Europe the computations of all
eclipses for each year as a part of its contribution. From
the British Office it first receives in exchange the positions of -
the Sun and moon for the entire year from which the data
required in the computation of eclipses are obtained.
The eclipse predictions that are made by the Nautical
Almanac Office at Washington are therefore used not only by
our own country but by many of the leading countries of
Europe as well.
VI
HOW ECLIPSES ARE PREDICTED
IT would not be in keeping with the purpose of this book
to enter into the mathematics of the eclipse problem. A con-
sideration of the methods and formulas used in the prediction
of eclipses would be a subject for a book in itself and would
be of interest chiefly to the mathematician or astronomer who
has to undertake the computation of eclipses. We will con-
sider here only a few points connected with the prediction of
eclipses that may be of general interest.
To compute a total eclipse of the moon is a comparatively
simple matter. An experienced computer will perform all
of the work necessary for the prediction of the times and cir-
cumstances in less than two working days of seven hours each.
But to compute all the elements of a total solar or annular
eclipse and find the latitude and longitude of all the positions
needed for the chart, which shows the outline of the shadow
}
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;
|
on the earth's surface, is very far from being a simple matter. J
In order to reduce to a minimum all chances of error in the
computation of eclipses it is the custom of the Nautical
Almanac Office to have two computers work independently,
and when possible, by different methods on the same eclipse.
The check computation of a total solar eclipse, which is a |
duplication of all the most important parts of the work and
a close check on the remainder, takes anywhere from ninety
to one hundred and twenty hours of close, exacting work while
the original computation will take considerably longer. At ,
least this has been the experience of the writer who has had
19
20 A HANDBOOK OF SOLAR ECLIPSES
the privilege of making the check computations of all eclipses
for the Nautical Almanac Office during the past fourteen
years. s
| A large total solar or anhular eclipse visible in equatorial
regions will take longer to º compute than a total solar or
annular eclipse visible in mid-latitudes because all of the
penumbral shadow, 4,000 miles or more in width, within which
only the partial phase of the eclipse is visible, lies on the
earth's surface. So the curves given on the charts are larger
and there are more of them to compute. On the other hand,
a partial solar eclipse, visible only in polar regions, for which
there is no path of total eclipse to compute, can be disposed
of in less than one-third of the time needed for a total
solar or annular eclipse in equatorial regions.
A glance at a chart of a total solar eclipse published in the
American Ephemeris will show that there are a number of
curves giving the position of the shadow at different times. .
} Most important of all is the path of total eclipse, never more
than 170 miles wide, usually much less, and about 5,000 miles
long, bounded by its northern and southern limiting curves,
as they are called. These two limiting curves are the most
troublesome and exacting of all curves to compute. The
central line of the eclipse, midway between the limiting curves
near which the scientific observer tries to locate, since here the
duration of totality is longest, can be disposed of very easily
by fairly simple computations. But the positions of two
diametrically opposite points one on each of the limiting
curves will take four or five times as long to compute, as the
point on the central line half way between them. A point
on the central line represents the position of the axis of the
moon’s shadow-cone at any instant but the two points, one on
each of the limiting curves, are on the circumference of the
HOW ECLIPSES ARE PREDICTED 21
shadow at opposite ends of the diameter passing through the
point on the central line. As the axis of the shadow traces
the line of central eclipse over the surface of the earth, the
points at the extremities of the diameter of the shadow trace
out the northern and southern limiting curves of the path of
total eclipse. One who is located within these limits will see a
total eclipse of the sun with duration longest on the central
line and shortest on the limiting curves. If the observer is
just without these limiting curves only a partial eclipse will
be seen, the magnitude of the partial phase decreasing with
distance from the limiting curves of total eclipse at the rate
of about five per cent. for every 250 miles.
In addition to the path of total eclipse a series of points
must be computed for locating the limits of the partial phase
of the eclipse outside of which no eclipse of the sun will be
seen. Except in eclipses in equatorial regions only one of
these limiting curves of the eclipse will fall on the earth's
surface, the other falling off into space beyond one pole of
the earth. Series of points must also be found for drawing
curves showing where the eclipse begins at sunrise and where
it ends at sunrise, as well as where the phase of the eclipse
is greatest at sunrise. Corresponding curves must also be
given for sunset. The first contact of the shadow with the
earth will be at a point where the sun is rising and the last
contact at a point where the sun is setting and the eclipse will
occur with the sun on the meridian midway between the sun-
rise and sunset curves. The region enclosed by the sunrise
and sunset curves and the limiting curves of partial eclipse
will represent that portion of the earth's surface within which
the eclipse will be observable. ---------
All of the work of eclipse prediction is done about four
years in advance and is then available, in the case of a total
22 A HANDBOOK OF SOLAR ECLIPSES
eclipse, to all those who are planning expeditions to the path
of totality. It speaks well for the exactness of modern astron-
omical calculations that the observer picks out his station with
the greatest confidence, though it lie in a strip only a few
miles wide, knowing that within a few seconds of the predicted
time the shadow of the moon will pass over him.
If the earth would obligingly stand still during the three
hours or so that the moon’s shadow is sweeping over it and if
it were as flat as the flat-earth theorists would like us to think
it is, the computer of eclipses would find his problem greatly
simplified. But as the shadow of the moon runs over the
earth from west to east the observer is also being carried east-
ward by the rotation of the earth at a rate that varies accord-
ing to his distance from the equator. The shadow of the earth
overtakes and passes him. It is the computer's problem to
find the trace of the rapidly moving lunar shadow over the
rapidly rotating earth that is not even a perfect sphere but
bulges at the equator and is flattened at the poles to an
extent great enough to have an appreciable effect upon the
position of the shadow path.
The computer attacks the difficulties of his problem by
first finding the projection of the moon’s shadow on a plane
through the earth’s center that is at right angles to the axis
of the shadow-cone. This plane he refers to as the funda-
mental plane. Then by appropriate formulas he transfers
the positions of the shadow in this plane to the rapidly rotat-
ing spheroidal surface of the earth.
How accurately, one may ask, can the times and circum-
stances of a solar eclipse be predicted? As far as the theory
is concerned, the times of beginning and ending of a total
solar eclipse can be computed as accurately as they can be ob-
served, to a fraction of a second. These times are computed
HOW ECLIPSES ARE PREDICTED 23
to the nearest hundredth of a second and published/to a tenth
of a second yet everyone who has ever observed a total solar
eclipse knows that the times may be, and usually are, “off”
by a number of seconds, often as many as twenty or more.
The trouble here is not with the eclipse theory nor the com-
puter but with unknown, and so far unexplained, irregularities
in the motion of the moon which produce discrepancies be-
tween its true position in the heavens and the positions pre-
dicted from the lunar tables, which are used in the computa-
tion of eclipses. :
Though the moon is one of the smallest members of the solar
system its position is the most difficult to predict and it has
caused the astronomers as much trouble as all the rest of the
satellites and planets combined.
The recent tables of the moon published in 1920 by Prof.
|F. W. Brown, one of the greatest mathematicians of the
present time, represent years of painstaking work and research
into that most difficult of all problems in theoretical astron-
omy, the motion of the moon. Yet the theory upon which
the construction of these tables is based does not explain
these small peculiarities in the moon’s motion and Prof.
Brown has expressed the opinion that there is something
affecting the motion of the moon that cannot be explained by
any existing theory of the moon’s motion. For any other
purpose except the computation of eclipses the position of the
moon is known accurately enough. It wanders in general not
more than twenty miles or so from its predicted position which
is only about one-hundredth of its own diameter, an amount
entirely inappreciable to the naked eye. That is, if two moons
were in the heavens, one in the theoretical position computed
from the tables and the other in the moon's true position they
would appear to the naked eye as one, though with the aid
24 A HANDBOOK OF SOLAR. ECLIPSES
of a telescope a slight overlapping of the disks could be de-
tected. -
This discrepancy between the true and computed position
of the moon, small though it is, is sufficient to introduce an
error of a number of seconds in the predicted times of Solar
eclipses and an error of two or three miles in the position of
the path of total eclipse. To correct this so far as possible
it has become customary to find a few weeks or months in
advance of eclipse day, just how much the true position of the
moon is differing from the theoretical position. This is done
by means of direct observations of the position of the moon
in the heavens. The times and duration of the eclipse and the
position of the path of total eclipse then receive small cor-
rections to make them conform with the latest observations
of the moon’s position and these corrections are published for
the benefit of those who are planning to make scientific obser-
vations within the path of total eclipse. For general pur-
poses of observation and for the eclipse charts the correc-
tions are too small to be appreciable. .
It is the custom of the Nautical Almanac Office to publish
a year or so in advance of the date of total solar eclipses
visible in the United States a special eclipse pamphlet for the
benefit of those who are planning to observe the eclipse. This
gives, in addition to the information given in the American
Ephemeris on the subject of the eclipse, the times and circum-
stances of the eclipse for a number of cities in the United
States, as well as meteorological data on weather conditions
at favorable points within the eclipse path and a large scale
map of the eclipse path within the United States. This was
done in the case of the eclipse of June 8, 1918, and the eclipse
of January 24, 1925 visible in New York and New England.
VII
SOMETHING FOR THE FLAT-EARTH THEORISTS
TO THINK ABOUT
THE question of the shape of the earth was thrashed out
pretty thoroughly some three centuries ago in the days of
Galileo. Yet we still have with us the flat-earth theorists, so
man-centered in their outlook that they still cling to the old
“lanterns-hung-out-in-the-heavens-for-man's-benefit” style of
universe with the earth the fixed and immovable center of all.
That the earth is spherical in shape and that it rotates on
its axis and revolves around the sun are not self-evident facts.
They require proof and it took some centuries to produce this
proof.
There are today a number of independent ways of estab-
lishing the fact that the earth is a sphere, or to be more exact,
a spheroid, slightly flattened at the poles and bulging at the
equator. Yet the most convincing arguments are not the
most easily understood and so we often read in school books
that we know the earth is round because it has been circum-
navigated. As a matter of fact we could circumnavigate a
banana-shaped world or a pear-shaped world. A far more
convincing argument is furnished by geodists or surveyors
who have measured arcs of meridians,—of great length in
Some instances, thus showing by direct measurement the
spheroidal shape of the earth. Also, we often hear or read,
as one proof of the earth’s sphericity, that the earth throws a
circular shadow over the moon at the time of lunar eclipse.
As a matter of fact, though, the outline of the earth’s shadow
25
26 A HANDBOOK OF SOLAR ECLIPSES
on the moon is very hazy and ill-defined owing to the presence
of an extensive atmosphere surrounding the earth which by
refraction of sunlight into the earth's shadow-cone greatly
blurs and dims the shadow outline. Then too a sphere is not
the only body that will cast a circular shadow.
Many of the proofs of the earth's sphericity at our dis-
posal today were not available in the time of Galileo but even
with his crude telescope he was able to see four of the Small
moons of Jupiter revolving around the huge planet and the
phases of Venus, which furnished a proof of its revolution
around the sun. Here, then, were spherical bodies in the
heavens that were not revolving around the earth, and by
analogy one might reasonably conclude that the earth also
was a spherical body in revolution about the sun. This form
of reasoning does not appeal to the flat-earth theorists today
any more than it did in the time of Galileo, though today the
modern telescope adds abundantly to the meager evidence fur-
nished by Galileo’s ‘optik tube.’ Possibly the flat-earth theor-
ists of the present day are like the learned man of three cen-
turies ago who refused to look through the telescope of Galileo
for fear he might see something to convince him -
There is no better proof of the fact that the earth is a
rotating spheroid in revolution around the sun than that fur-
nished by the results of the astronomical predictions of total
Solar eclipses when taken in connection with the fact that
observations of eclipses within the shadow tracks have proven
the predictions to be correct. This is a proof not generally
given because it requires some knowledge of the manner in
which solar eclipses are predicted to appreciate its force.
If our flat-earth theorists will procure some back numbers
of the American Ephemeris for sixty years or more or some
English Nautical Almanacs or copies of the Connaissance des
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SOMETHING TO THINK ABOUT 29
Temps of the French, going back, for their purpose, a hundred
years or so, they will be impressed with the odd form of the
tracks of total solar eclipses over the earth's surface. Their
general characteristics are great length, frequently five thous-
and miles or over, extreme narrowness, being always under
170 miles and often less than 100 miles, and their peculiar
curvature, particularly in high latitudes. Now for nearly
one hundred years astronomers have been making scientific
observations of total solar eclipses within these eclipse tracks.
In some instances they have travelled half way around the
world, when these tracks have fallen in out of the way places
or over unavailable ocean expanses, in order to be within the
eclipse path at the specified time. Often when the path has
fallen in well-populated regions of the world the entire path
of the eclipse has been thickly studded with observers scien-
tific and otherwise. In the case of the total solar eclipse of
July 29, 1878, which was visible in the United States and
Canada, it has been said that observers were scattered so
thickly along the path that it resembled one continual obser-
vatory, and fortunately, they were rewarded with perfect
weather conditions at most stations and a glorious coronal
display.
Any number of instances might be given of observations
of total eclipses made at widely separated stations within the
long, narrow, curved path of the moon’s shadow, and in all this
period covered by the scientific observation of total solar
eclipses we find no record of failure on the part of the astron-
Omers to correctly predict the course that would be followed
by the shadow of the moon. The first American eclipse ex-
pedition, to Penobscot in October 1790 did, to be sure, find
itself just without the path of total eclipse owing possibly to
an error in the lunar tables then in use or to imperfections
30 A HANDBOOK OF SOLAR ECLIPSES
in the methods of predicting the limiting curves of the eclipse.
This rather strengthens the point we would make, however,
as the astronomical elements and constants upon which the
prediction of eclipse depend were not known to the same
degree of accuracy in those days as they are at the present
time, nor were as precise methods of computation employed.
Granted, then, that the paths of total solar eclipses are cor-
rectly computed and do represent the course of the moon’s
shadow over the face of the earth, how does that prove that the
earth is round, that it rotates and that it revolves around the
sun ? We would suggest here that the doubter study in de-
tail the fundamental theory and formulas upon which the
prediction of eclipses rest but we may say briefly that the
entire fabric of eclipse calculations rests upon assumptions as
to the form and size of the earth, its distance from the sun
and from the moon and the rate at which it is turning on
its axis and revolving around the sun. If any of these assump-
tions were wrong the track of a total solar eclipse over the sur-
face of the earth would not fall where the astronomer says it
will fall.
Indeed the accuracy now obtainable in the calculation of
solar eclipse paths may be taken as a proof of the correctness
of some of the most fundamental conceptions of astronomy.
If there were a mistake in the estimate of the size of the earth,
Sun, or moon, or of the relative motions and distances of these
three bodies or even in the small amount of the flattening of
the earth at the poles it would show up in the results of the
eclipse calculations, in the position and width of the shadow
track and in the times and duration of total eclipse.
It may well be considered one of the foremost achievements
of astronomy of today that from theory alone the course of
the moon’s shadow over the face of the earth can be predicted
SOMETHING TO THINK ABOUT 31
in advance with an error not exceeding three or four miles at
most. It is expected that the cause of the slight discrep-
ancies now existing between observations and theory and due
to irregularities in the motion of the moon will in time be
discovered and eliminated. If our flat-earth friends question
the correctness of these fundamental assumptions upon which
the prediction of eclipses rests let them try to predict eclipses
upon the basis of their flat-earth theory !
VIII
PAST TOTAL SOLAR ECLIPSES IN THE EASTERN
PART OF THE UNITED STATES
IN the three hundred years and over that have elapsed since
the Pilgrim fathers landed in New England, there have been
but seven total eclipses of the sun visible in this part of our
country.
These eclipses occurred respectively on November 14, 1659,
August 22, 1672, July 12, 1684 (total-annular), January 19,
1768 (total-annular), June 24, 1778 and June 16, 1806.
There have been in addition an equal number of annular
eclipses of the sun visible in the same section.
The first total solar eclipse in the British colonies of which
there is any record was the eclipse of June 24, 1778, a splendid
eclipse of four minutes duration occurring near noontime.
The path of this eclipse passed from Lower California across
some of the southern states to the Middle Atlantic States and
New England. After leaving the North American coast it
crossed the Atlantic to Spain and thence to North Africa,
where it left the earth at sunset.
David Rittenhouse of Philadelphia, one of the earliest of
American astronomers, observed this eclipse, as did also Prof.
Samuel Williams at Bradford, Mass. In writing of his ob-
servations, Prof. Williams says, “The dew fell so fast as to
wet the paper we were using to a considerable degree.” This
eclipse was also observed at sea by the Spanish Admiral Don
Antonio Ulloa, while passing from the Azores to Cape St.
32
PAST TOTAL ECLIPSES 33
Vincent. Ulloa evidently viewed the eclipse under a perfect
sky for he made very complete observations for those days
including a drawing of the corona which he refers to as a
“luminous ring,’ the present name of corona being then un-
known. He also records the appearance of the brighter
stars and the effect of the eclipse upon members of the crew
and animals on board, and describes an apparent ‘hole' in
the disk of the moon during eclipse which was doubtless a
solar prominence. This eclipse may possibly have been visible
in New York City though there is no record of observations
being made there. -
The next eclipse, that of October 21, 1780, came down from
Baffin Land and Hudson Bay to the St. Lawrence River and
Maine. It is of special interest because it was the first
eclipse for which an American eclipse expedition was planned
and sent out. Though it occurred during the Revolutionary
War, the British garrison at Penobscot granted a request
that an eclipse party be permitted to choose a suitable place
in that vicinity for observing the eclipse. Consequently the
Commonwealth of Massachusetts sent an expedition to Penob-
scot by vessel under the direction of Prof. Samuel Williams
of Harvard. This expedition, unfortunately, failed to get
quite within the path of totality, owing probably to inaccura-
cies in the tables giving the position of the moon; so only the
phenomenon known later by the name of Baily’s Beads was
observed, the corona or “luminous ring,’ as it was then called,
not being visible.
The next point of interest in the history of eclipse observa-
tions in New England was the observation of the annular
eclipse of April 3, 1791, by Prof. Webber at Harvard. The
sky was perfectly clear and the annulus was observed for
34 A HANDBOOK OF SOLAR ECLIPSES
nearly five minutes. Prof. Webber records the predicament
he was in as a result of his clock stopping the day before the
eclipse and the goodness of the President of the University,
whose clock had not played such an unkind trick at a critical
time, in asking him to observe the eclipse with him.
The eclipse of June 16, 1806, the last total solar eclipse to
be observed in this part of the country, up to the present
time, was a fine eclipse of more than four and a half minutes
duration, which is considerably more than the average length
of totality. It also occurred near noon and was total at
Ogdensburg, Albany, and Kinderhook, N. Y., and Salem,
Mass. DeWitt observed the total phase of the eclipse at
Albany for about four minutes and fifty seconds, the Spanish
astronomer Don Joaquin Ferrer for four minutes thirty-seven
seconds at Kinderhook, near the Hudson, and the well-known
astronomer Bowditch recorded his observations at Salem,
Mass. Of the appearance of the corona he says simply,
“The whole of the moon was then seen surrounded by a
luminous appearance of considerable extent such as has gen-
erally been taken notice of in total eclipses of the sun.” In-
deed little is said regarding the corona until the occurrence of
the total eclipse of July 8, 1842, which was observed in one of
the most thickly populated parts of Europe and which may
be said to have ushered in the period of the New Astronomy.
Several observers recorded the appearance of the corona sev-
eral Seconds before the beginning of totality, an unusual
occurrence, and the fact began to be recognized that it was a
solar appendage of peculiar interest and scientific importance.
The eclipse of 1806 was the last total solar eclipse to visit
the northeastern part of the United States up to the present
time. The eclipse of May 28, 1900 was total in the southern
PAST TOTAL ECLIPSES 35
states from New Orleans through Georgia to North Carolina
and Norfolk, Va., but it was only a large partial eclipse in
Pennsylvania, New York and New England. Although the
duration of this eclipse was less than two minutes in the United
States there were many expeditions in the field and it was
one of the most successfully observed eclipses of recent years.
IX
THE TOTAL SOLAR ECLIPSE OF JANUARY 24, 1925
AFTER an interval of nearly one hundred and twenty years,
on the twenty-fourth of January, 1925, the path of a total
eclipse of the sun will pass once more over the northeastern
section of the United States. Up to this time there has been
no total eclipse of the sun visible in New York, Pennsylvania,
or New England since June 16, 1806 and not until the year
2024 will another total eclipse be visible in the same part of
the United States. The sun may rise eclipsed at Boston on
October 2, 1959 but the path of the eclipse will then pass off
to Sea.
The path of the eclipse of next January will first strike the
earth in Minnesota at sunrise a little to the east of Red Lake.
From here it will pass in a southeasterly direction over the
Great Lakes, northern Minnesota, Wisconsin, Michigan, a
small section of Canada, to Niagara Falls and Buffalo, N. Y.
The total phase of the eclipse will begin here shortly after
nine o’clock in the morning, Eastern Standard Time, with the
sun about 13° above the horizon. The path of totality will
pass from Buffalo in a southeasterly direction, to that part of
the Atlantic coast which lies between New York City and the
extreme southern part of Massachusetts, in a strip about one
hundred miles wide and over four hundred miles long across
the most densely populated part of the United States. In-
cluding New York City, which lies on the southern limit of
the eclipse, with the harbor, Battery and lower part of the
city, just without the path, and the northern part of the city
36
ECLIPSE OF JANUARY, 1925 37
within it, there will be approximately ten million people
within the path of total eclipse not including the number that
will come to the path from points outside.
The central line of the eclipse, the trace of the axis of
the moon’s shadow-cone across the earth's surface, will pass
almost directly over Buffalo, Watkins, at the head of Seneca
Lake, and Binghamton. It will cross the Hudson River at a
point between Newburgh and Poughkeepsie and pass over
Danbury and New Haven, Conn. to Gardiners Island and
Montauk Point. -
As the shortest distance from the central line to the north-
ern or southern limit of the path of total eclipse is about fifty-
one or fifty-two miles all points within this distance of the
central line on either side will be within the path of total
eclipse.
The northern limit of the eclipse will pass from a point in
Wayne Co., N. Y. on Lake Ontario to a point about six miles
South of Syracuse, and about five or six miles south of Morris-
ville and Cooperstown, N. Y., striking the Hudson about
twenty-two miles south of Albany. It will cross the south-
western part of Massachusetts passing about two miles south
of Springfield, Mass., to the extreme northeastern corner of
Connecticut, and directly through Rhode Island to a point
less than two miles south of Providence. It then passes
through the extreme southern part of Massachusetts less than
five miles north of Fall River and New Bedford to a point on
Nantucket Sound, a few miles southwest of Barnstable on
Cape Cod.
The Southern limit of the path of total eclipse passes from a
point on Lake Erie six miles north of Mayville, N. Y., across
the extreme southwestern corner of New York State to Penn-
Sylvania running about five miles south of Wellsboro, Penn.,
38 A HANDBOOK OF SOLAR ECLIPSES
and about an equal distance north of Wilkes-Barre. Morris-
town and Newark, N. J., lie about eight miles outside of the
southern limit and Paterson and Hackensack, N. J. about an
equal distance within the limit. The northern part of Jersey
City lies directly on the southern limit of totality and Brook-
lyn and Jamaica, Long Island, just outside. Mineola, L. I.
will be about five miles within the southern limit.
After leaving Long Island and the New England Coast,
the path of total eclipse crosses the North Atlantic in a north-
easterly direction. The eclipse will occur at noon at a point
in approximately 44 west longitude and 42 north latitude, and
it will pass off the earth at sunset at a point between the
Shetland and Faroe Islands. Following the discouraging
practice of eclipse paths in general it wastes, from the point
of view of the astronomer, the best part of its path in mid-
ocean since it does not touch land once after leaving Nantucket
on the New England coast. The longest duration of the
eclipse will occur near the middle of its path in the Atlantic
ocean where the sun is at its highest altitude above the horizon.
The longest duration in the United States will be on the cen-
tral line on the New England coast. The most favorable
points for observation should be on the Hudson and in Con-
necticut in the vicinity of New Haven. As the duration of
totality always decreases with distance from the central line
it is advisable that those who wish to observe the eclipse should
get well within the path of totality. Also, as explained in an
earlier chapter, uncertainties in the moon’s position make the
exact position of the northern and southern limits doubtful
to the extent of two or three miles. As the corona cannot be
seen so long as the least percentage of sunlight remains and as
the glory of the eclipse lies in the corona, it is advisable for
this reason alone to get within the northern and southern
SOUTH
A M E R C. A
|OO BO 6O
40
tº
2O
aff wrºp water sº, ºw& ºvern. dºc asze
- º
1925. *g, *.*.*
tº
*
Chart showing path of Total Solar Eclipse of January 24,
.
:

ECLIPSE OF JANUARY, 1925 41
limits by a safe margin of at least ten miles. In the western
part of New York the sun will be at such a low altitude that
it will be essential to choose a point of observation command-
ing an unobstructed view of the southeastern horizon. At
Duluth, Minn., the altitude of the sun will be only 2° at the
time of total eclipse and no observations of any scientific value
can be expected west of New York State or possibly Toronto
in Canada. In the vicinity of the Hudson River, and in Con-
necticut, the sun will be at an altitude of nearly 20° so the
conditions should be more favorable in this section. It is also
advisable to choose, if possible, an observing station at a con-
siderable elevation above the surrounding country. This
is imperative if one wishes to watch for the approach of the
moon’s shadow which sweeps down from the west with the
frightful velocity of half a mile a second. This is one of the
most impressive features of the eclipse but one that is rarely
observed. Here aviators have the advantage over all other
observers. Indeed when it comes to viewing a total eclipse
as a scenic feature, the aviator is at a most decided advantage
for he can in general rise above low-lying fogs and clouds and
be fairly certain of an unobstructed view. Like the man
aboard ship, however, he is at a disadvantage when it comes to
making scientific observations with telescope and spectroscope
for here a firm foundation and mounting for the instruments
is of prime importance.
It may seem to the general reader that it would be impossible
to make observations of great scientific value in such a brief
period as one and a half minutes. Yet it may be recalled that
the eclipse of June 8, 1918 that was so successfully observed by
expeditions from the Lick, Yerkes and United States Naval
Observatory parties in points in Oregon, Washington, and
Colorado, had a maximum duration of less than two minutes.
42 A HANDBOOK OF SOLAR ECLIPSES
Also one of the most successfully observed eclipses and one of
which the most complete records have been obtained was the
eclipse which occurred on New Year's Day 1889. The path of
totality of this eclipse ran across the North American con-
tinent from California to Manitoba, and the sky was clear
practically everywhere. Though the duration of this eclipse
was less than two minutes in the United States, a wealth of
drawings and photographs were obtained and many addi-
tional scientific observations were made at a large number of
stations. So we may say that the briefness of the eclipse
alone will not prevent the astronomers from securing many
valuable observations provided the skies are clear at even one
or two stations, during the few critical moments. Of greater
concern to the astronomer is the fact that the coming eclipse
will occur at an unfavorable time of day when the sun is not
far above the horizon and at an unfavorable time of year when
stormy weather is most general. Yet when it comes to con-
sidering weather conditions, a passing cloud on a summer's
day or a sudden shower in spring might prove to be just
as fatal as a snow storm in winter. The weather has played
odd jokes on eclipse expeditions in the past, often when and
where least expected, as in the eclipse of Sept. 10, 1923 when
fair weather occurred in Mexico, where it was least expected,
and the sky was heavily overcast with clouds where most
favorable weather conditions had been promised, in Lower
California.
A most interesting feature of the coming eclipse, unique
in the history of eclipse observations is the fact that ten ob-
servatories will lie directly within the path of total eclipse
while there will be thirteen more within less than fifty miles
of the northern and southern limits of the eclipse. The ob-
servatories within the path include the observatory of the
ECLIPSE OF JANUARY, 1925 43
University of Toronto, in Canada, Fuertes Observatory, Corn-
ell University, Ithaca, N. Y., Smith Observatory, Geneva, N.
Y., Elmira College Observatory, Elmira, N. Y., Observatory of
the Bausch and Lomb Optical Co., Rochester, N. Y., Columbia
University, New York City, Vassar College Observatory,
Poughkeepsie, N. Y., Wesleyan University Observatory, Mid-
dletown, Conn., Yale University Observatory, New Haven,
Conn., and Maria Mitchell Observatory, Nantucket.
The thirteen observatories within less than fifty miles of the
limits of the path of total eclipse where there will be an
eclipse of 99% or more are at Albany, N. Y., Amherst, Mass.,
Cambridge, Mass., Clinton, N. Y., New Brunswick, N. J.,
Northampton, Mass., Princeton, N. J., Providence, R. I.,
South Bethlehem, Penn., South Hadley, Mass., Syracuse, N.
Y., Wellesley, Mass. and Williamstown, Mass. The Sproul
Observatory of Swarthmore College which sent an expedition
to Mexico to observe the 1923 eclipse, will be about 75 miles
from the southern limit of the eclipse path and the magnitude
of the eclipse will be 98% at that point.
A partial eclipse of 95% or more will occur at some of the
largest cities in the United States including Chicago, Phila-
delphia, Boston, Baltimore, Washington, Pittsburgh, Cleve-
land, Detroit, Toledo, Albany, and Ottawa and Montreal in
Canada. In general there will be a decrease of about one
per cent in the magnitude of the eclipse for every forty miles
in distance from the northern or southern limit of the path
of total eclipse, so the magnitude of the eclipse at any point
outside the path of totality can be estimated approximately by
measuring its distance from the nearest limit of the path.
The popular interest in the eclipse will be great owing to
the fact that there will be no other total solar eclipse visible
in this section for nearly one hundred years to come and the
44 A HANDBOOK OF SOLAR ECLIPSES
scientific interest will be keen because of the large number of
observatories and scientific institutions that lie within or close
to the path of the eclipse. Here at last the astronomers have
an eclipse that may not, it is true, offer as favorable circum-
stances as might be desired, but which will, nevertheless,
knock at their very doors. Let it be hoped that the weather-
man will not fail to provide a suitable setting for the scene.

CIRCUMSTANCES OF THE TOTAL SOLAR ECLIPSE OF JANUARY 24, 1925 FOR SOME OF
THE PRINCIPAL TOWNS WITHIN THE LIMITS OF THE ECLIPSE.
1. Principal Towns Within the Path of Total Eclipse.
#;"#. | Mid-Totality pajá, Duration
Duluth, Minn.” . . . . . . . . . . . . . . . . tº C tº - 8 h 0 m. 9 h 9 m 0.5 m
Hamilton, Canada . . . . . . . . . . . . . 7 h 59 m E.S.T. 9 6 10 21 1.8
Toronto, Canada . . . . . . . . . . . . . . 7 59 & & 9 7 10 22 1.0
Buffalo, N. Y. . . . . . . . . . . . . . . . . . 7 59 & & 9 7 10 22 1.8
Ithaca, N. Y. . . . . . . . . . . . . . . . . . . 8 0 & & 9 10 10 26 1.8
Geneva, N. Y. . . . . . . . . . . . . . . . . . 8 0 & & 9 10 10 26 1.8
Binghamton, N. Y. . . . . . . . . . . . . 8 0 & & 9 11 10 27 1.8
Poughkeepsie, N. Y. . . . . . . . . . . . . 8 1 ( & 9 12 10 30 1.9
New York, N. Y. . . . . . . . . . . . . . . 8 0 { { 9 11 10 29 0.5
New Haven, Conn. . . . . . . . . . . . . . 8 1 & & 9 13 10 32 2.0
Circumstances of the Total Solar Eclipse of Jan. 24, 1925 for Some of the Principal Towns Within the
Limits of the Eclipse.—Continued.
2. Principal Towns for Which the Greatest Eclipse Is Ninety-five Per Cent. or Over.
|Beginning of Greatest End of & Distance to
E.; #. Eclipse Partial Eclipse Magnitude Nº.ge
Albany, N. Y. . . . . . . . . . 8 h 2 m E.S.T. 9 h 13 m 10h 31 m 99% 22 mi.
Augusta, Me. . . . . . . . . . . . .] 8 8 é & 9 21 10 41 96 200
Baltimore, Md. . . . . . . . . . 7 56 & 4 9 5 10 23 96 150
Boston, Mass. . . . . . . . . . . . 8 4 & & 9 17 10 36 99 45
Cleveland, Ohio. . . . . . . . . . 6 55 C.S.T. 8 3 C.S.T. 9 17 97 100
Chicago, Ill.” . . . . . . . . . . . • • - e 7 58 & 4 9 9 95 200
Detroit, Mich.* . . . . . . . . . tº e º g 8 3 & 4 9 16 98 75
Harrisburg, Pa. . . . . . . . . . 7 57 E.S.T. 9 6 E.S.T. 10 24 98 85
Lansing, Mich.* . . . . . . . . . . . . - 8 0 C.S.T 9 13 98 80
Madison, Wis.” . . . . . . . . . 7 58 & 4 9 8 95 165
Minneapolis, Minn.” . . . . . tº de 7 58 & 4 9 6 96 135
Montreal, Canada . . . . . . . 8 6 E.S.T 9 15 E.S.T. 10 34 95 235
Newark, N. J. . . . . . . . . . . . 8 0 ( & 9 11 & & 10 29 99-H 5
Ottawa, Canada . . . . . . . . . 8 5 ſ & 9 14 & 4 10 30 96 190
Pittsburgh, Pa. . . . . . . . . . 7 55 & & 9 3 & & 10 18 96 160
Philadelphia, Pa. . . . . . . . . 7 58 { { 9 8 & & 10 26 98–H 80
Providence, R. I. . . . . . . . . 8 3 & & 9 15 & & 10 35 99-H 2
Toledo, Ohio.” . . . . . . . . . tº e º ſº 8 2 C.S.T 9 14 96 125
Trenton, N. J. . . . . . . . . . . . 7 58 6 & 9 8 E.S.T. 10 27 99 50
Saginaw, Mich.* . . . . . . . . tº e e 8 2 C.S.T 9 16 99-H. 20
Springfield, Mass. . . . . . . . 8 2 & 4 9 14 E.S.T.ſ 10 33 99–H 2
Syracuse, N. Y. . . . . . . . . . 8 1 & 4 9 11 & & 10 27 99–H 8
Washington, D. C. . . . . . . . 7 55 ( & 9 4. é & 10 22 95 190
§

Circumstances of the Total Solar E
clipse of Jan. 24, 1925 for Some of the Principal Towns Within the
Limits of the Eclipse.—Continued.
3. Principal Towns for Which the Greatest Partial Eclipse Is Less Than Ninety-five Per Cent.
Beginning of
Partial Eclipse
Greatest Eclipse
Atlanta, Ga. . . . . . . . . . . . . .
Austin, Tex.” . . . . . . . . . . . .
Bismark, N. D.; . . . . . . . . . .
Cheyenne, Wyo.f
Cincinnati, Ohio
Columbia, S. C. . . . . . . . . . .
Columbus, Ohio. . . . . . . . . . .
Denver, Colo.f
Des Moines, Iowa.” . . . . . . . .
Kansas City, Mo.”
New Orleans, La.”
Omaha, Neb.”
Raleigh, N. C. . . . . . . . . . . . .
Santa Fe, N. Mex.f
Springfield, Ill.”
St. Louis, Mo.”
* e º e º a dº º º e ºs
6 h 46 m C.S.T.
6 5i “
6 47 é &
6 53 & &
7 h 50 m E.S.T.
7 h 50 m C.S.T.
7 38 & 6
h
57
54
59
53
49 m
42
51
59
53
51
& 4
& 4
& &
& 4
& &
E.S.T.
C.S.T.
End of
Partial Eclipse
9 h 3 m. C.S.T.
8 38 & &
9 1 & &
7 49 M.T.
9 10 C.S.T.
9 9 & 4
9 13 & 4
7 47 M.T.
9 1 C.S.T.
8 h 56 m ‘‘
8 48 £ &
8 58 é &
10 15 E.S.T.
7 40 M.T.
9 3 C.S.T.
9 1 { {
Magnitude
80 %
61
(59)
(41)
91
83
94
(41)
90
84
67
87
88
(36)
89
86
*Sun Rises Partially Eclipsed.
+Greatest Eclipse Takes Place With Sun Below the Horizon.
*
X
THE PARTIAL SOLAR ECLIPSE
THE first stage of a solar eclipse begins when the edge or
rim of the moon, “limb' the astronomer calls it, first comes
into contact with the edge of the sun. Needless to say this
contact is apparent only, for the moon is nearly ninety-three
million miles this side of the sun and the only reason that it
can hide a body four hundred times greater than itself in
diameter is because it is four hundred times nearer.
If you chance to be near an eclipse camp somewhere within
the belt of totality when the partial phase of the eclipse be-
gins you will hear some astronomer who is looking through a .
telescope call out ‘first contact’ and you will know the eclipse
is ‘on.” More than an hour later, usually, ‘second contact’
will take place when the sun is completely covered by the moon
and the total phase of the eclipse begins. ‘Third’ and “last’
contact will follow in turn with the ending of totality and
the ending of the partial eclipse.
If you don't happen to be near an astronomer or someone
who is in possession of a telescope at the time of first contact
the chances are that you will not know the eclipse has begun
until the moon has notched a considerable piece out of the
western rim of the sun. It is not easy to tell just when the
lunar disk first touches that of the sun and the eclipse starts,
even if you are looking through a telescope, for, obviously,
you cannot see the moon until its dark rim is visible against
the luminous surface of the sun and then the eclipse has
already started. The times of first and last contact of sun
48
PARTIAL SOLAR ECLIPSE 49
and moon are of no scientific value because they cannot be de-
termined to any great degree of accuracy. The times of
second and third contact which are the times of beginning and
ending of totality can be observed to a very high degree of
accuracy, however, because of the nature of the phenomena
that attend them, and they are of very considerable scientific
value since they furnish a means of comparing the true and
predicted positions of the moon at a given time, which gives
a check on the accuracy of the tables of the moon used in pre-
dicting eclipses as well as a means for improving these tables.
If you are outside the belt of total eclipse the partial phase
of the eclipse is all that you are going to see and this is of
no scientific interest and of little general interest unless the
magnitude is at least 95%. Of course the nearer you are to
the belt of totality the larger and more interesting the partial
phase will be but after all it is the total phase and its unique
and impressive phenomena that everyone wants to see and if
you are a few miles outside the path you will find that it will
be well worth while to put yourself a few miles inside of it.
After the first contact there is little to watch during the
partial phase except the slow and gradual encroachment of
the moon upon the solar disk and a slow and gradual decrease
in the light of the sun up to the time of greatest obscuration.
The magnitude of the greatest eclipse will vary inversely with
the distance of the observer from the central line of total
eclipse. At a distance of two thousand two hundred miles or
so from the central line the eclipse will not be much more than
a mere grazing contact of sun and moon. By magnitude of
the eclipse for any place we mean the per cent of the sun’s
diameter that is covered at greatest obscuration by the moon
and not the per cent of solar surface that is covered as appears
to be quite generally believed.} For example, if you read that
50 A HANDBOOK OF SOLAR ECLIPSES
a certain solar eclipse will have a magnitude of 75% at your
city that means that 75% of the sun's diameter will be covered
at greatest eclipse at that place and not 75% of the surface.
After greatest obscuration occurs at any place the moon is
observed to recede slowly from the solar disk, last contact tak-
ing place at the eastern edge of the sun since the moon crosses
the face of the sun from west to east.
If the partial eclipse is large, say over 90%, the solar
crescent at time of greatest eclipse will be very thin and as a
result the light will be reduced to a sort of weird twilight,
only stronger than twilight in its intensity. The landscape
will take on a peculiar hue and the image of the sun wherever
it is formed will be noticeably crescent-shaped. This has been
particularly noted in the case of sunlight sifting through the
interstices between leaves on trees or hedges, the images falling
on the ground in the form of series of crescents presenting a
weird and unnatural effect. The writer recalls that when at
recitation class in mathematics at Cornell University, Ithaca,
N. Y., during the maximum obscuration at that point of the
eclipse May 28, 1900, total at Norfolk, Wa. several hundred
miles away, the Professor who was conducting the class turned
the seat of a cane-bottomed chair with its regular rows of
circular openings toward the sun so that a series of images
of the thin solar crescent fell in rows and columns on the
floor. There are many ways in which images of the solar
crescent can be formed, one way being to turn a pair of
binoculars toward the sun and focus the image on a sheet of
white paper or cardboard, held a foot or so from the eye-end.
Care should always be taken not to look directly toward the
sun either with the naked eye or through binoculars or tele-
scope without using a dark glass cap or smoked glass. If this
PARTIAL SOLAR ECLIPSE 51
precaution is not taken serious injury to the eyes or blind-
ness may result.
The time of last contact can be determined more accurately
than the time of first contact because the dark rim
of the moon can be followed to the point of disappearance
more readily than it can be discovered at the instant of first
contact. The entire duration of the partial eclipse will vary
for different points. It will be longest at points close to
the limits of total eclipse where the eclipse is greatest and
extremely short at points near the outer limits of the penum-
bral shadow, as it is called, within which only partial phases
of the eclipse are visible. For example, in the case of the
total solar eclipse of January 24, 1925, the entire duration of
the partial eclipse at Albany, N. Y., a little over twenty miles
outside the northern limit of total eclipse, where the magnitude
is 99%, is two hours twenty-nine minutes, while at Panama
over two thousand miles away where the magnitude is 19%
the duration of partial eclipse is one hour twenty-six minutes.
If weather conditions are fair along the northern and south-
ern limits of the path of total eclipse during the eclipse of
January 24, 1925 an excellent opportunity will be afforded to
determine how close the predicted positions of these curves
agree with the true positions. These limits will pass over
or close to some of the largest cities in the country including
New York City, and Syracuse, N. Y., Wilkes-Barre, Pa., and
Springfield, Mass. and Providence, R. I. As we will see in
the next chapter, it is possible to tell by the nature of the
phenomena observed whether the station is within the path of
totality or just outside and for the first time in the history of
eclipse observations it may be possible to tell as a result of
observations made by those located close to the predicted
positions of these curves, how much the predicted positions are
52 A HANDBOOK OF SOLAR ECLIPSES
in error as a result of uncertainties in the position of the
moon. The astronomer interested in the scientific problems
that are associated only with total eclipse is not going to lose
the opportunity of making valuable observations by taking a
station dangerously close to the limits of the belt of totality.
Here is a chance, then, for the general observer who happens
to be located close to the limiting curves to aid in the location
of the exact limits of total eclipse by recording the phenomena
that he observes during the maximum phase of the eclipse at
his station. New York City will be a particularly favorable
location for observations of this kind owing to the fact that
the predicted southern limit passes directly through the down
town section. Here, then, is an opportunity to check up on
the accuracy of a predicted eclipse curve! If the moon is
keeping no better to its prescribed path at eclipse time than
it has been in the habit of doing in the past few decades, it is
safe to predict that the calculated limits of total eclipse may
be “off” as much as three miles or so from the true positions.
By observations made in the vicinity of these curves it
will be possible to tell how much the predicted positions are
in error. How much the predicted times of the beginning and
ending of total eclipse are in error will be known when the
times of second and third contact are recorded by observers
stationed within the belt of total eclipse. In extreme cases
these have been found to be in error by nearly as much as
thirty seconds.
XI
SHADOW BANDS
9 :SHORTLY before the beginning of total eclipse, usually five
minutes or less, faint, shimmering, wave-like bands of light
and shade known as shadow bands are frequently seen flitting
over the ground or sides of buildings. Records of the obser-
vations of these shadow bands are often very contradictory
even when the observers of the phenomenon are at the same
place. Some may see them while others do not. At some
eclipses they are very conspicuous, at other śclipses they will
be very faint or indistinct or not visible at all. They are
usually, but not always, seen just after, as well as just before,
total eclipse.
The shadow bands vary in width and velocity as well as in
distinctness but they usually move very slowly, in general
about six or eight miles an hour, and the direction in which
they are moving seems to be the same as the direction in
which the shadow-cone is moving. Their slow motion shows
that they do not accompany the shadow-cone which moves
across the earth with an average velocity of about twenty-five
miles a minute.
The cause of the shadow bands seems to lie in the atmos-
phere of the earth itself, that is, they are believed to be a
meteorological effect produced either by irregularities in the
refraction of the light from the rapidly dwindling crescent of
sunlight or due possibly to changes in the density of the air
following the sudden drop in temperature at this phase of the
eclipse. here is much that is peculiar in the behavior of
f 53
i
* .
i (. . . . t.
-> * -”
* ..]
f º
2- C
, ºw
*—2

54 A HANDBOOK OF SOLAR ECLIPSEs
the shadowbands, however, and it cannot be certain that the
above explanation is the true one until the phenomenon has
been more generally observed and if possible, photographed.
Up to the present time all efforts to photograph the shadow
bands have been unsuccessful. So here is an opportunity for
someone to accomplish a difficult photographic feat. The co-
operation of the general observer in the observation of shadow
bands is always welcomed by the astronomer who is so oc-
cupied with observations connected with the total phase of the
eclipse, which begin at nearly the same time, that he has
little opportunity to study this interesting phenomenon which
belongs in the field of meteorology rather than astronomy.
The best way to observe the shadow bands is to stretch a
large sheet on the ground and as soon as the bands appear,
a few moments before totality, note the time of appearance,
and then the general direction in which they are moving by
laying a rod on the sheet parallel to the direction of motion.
Leave the rod lying in the position placed until after the end
of totality when the direction can be determined at leisure.
Also have a second sheet prepared to observe the phenomenon
just after totality, if it should appear. Estimate the width
of the bands and the distance between crests of the waves,
how fast they are moving and whether they come singly or
in groups. - -
The great difficulty in photographing the shadow bands lies
in the fact that the general illumination is very faint at this
time while the bands are wavy, indistinct and shimmering in
their effect, much like the reflection of sunlight from rippling
water. A highly sensitive film and the highest photographic
skill will be required to catch them.
Some attention has been given to the problem of photo-
graphing the shadow bands in the research laboratories of
***
He Solar Corona photograph by Lick-Crocker Eclipse Expedition,
. Wallal, Australia, September 21, 1922.


SHADOW BANDS 55
the Eastman Kodak Co., and Dr. L. E. Jewell of that com-
pany has found that an extremely rapid combination could be
obtained by using in succession some “gun-sight” achromatic
lenses. -
The Yerkes Observatory Eclipse Expedition which was
stationed on Catalina Island to observe the total solar eclipse
of September 10, 1923 planned to attempt the photography of
the shadow bands with a set of three such lenses using a
“Hurricane” plate and an exposure of one-hundredth of a
second. Unfortunately these plans as well as many other
eclipse plans were defeated by cloudy skies. It is to be hoped
that the coming eclipse of January 24, 1925, will present a
favorable opportunity for photographing the shadow bands,
particularly as the path of totality will pass directly over the
research laboratories of the Eastman Kodak Co. at Rochester,
N. Y. where if anywhere, success should be attained in photo-
graphing this elusive phenomenon. It is possible that a
movie camera fitted with a film of superspeed could also be
used successfully for this purpose.
To show how differently the shadow bands may appear to
two observers both skilled in making astronomical observations
and stationed, moreover, at the same point we are quoting
below from the descriptions of the shadow bands given by Mr.
A. D. Ross, Professor of Astronomy and Physics in the Uni-
versity of Western Australia, who was a volunteer member of
the Crocker Eclipse Expedition of the Lick Observatory to
Wallal, Australia to observe the total solar eclipse of Sep-
tember 21, 1922, and Professor J. L. Chant of the Toronto
Eclipse Expedition, who also observed the shadow bands at
the same time and place. These excellent descriptions of the
shadow bands will also give the general reader an idea of the
manner in which this interesting phenomenon is observed and
56 A HANDBOOK OF SOLAR ECLIPSES
what he may expect to see, if he is fortunate enough to be
within the path of totality.
The following is taken from the description of the shadow
bands by Professor Chant appearing in the Journal of the
Royal Astronomical, Nov.-Dec., 1923. -
“Suddenly, and before I had expected it, the shimmering,
elusive, wave-like shadows began to sweep over me and the
sheet. I grasped the rod and moved it back and forth until
it was parallel to the crests of the waves as they moved for-
ward. At the same time I began counting seconds—‘one-and,
two-and, three-and, etc.’—and I continued counting up to 150
before totality was announced. I think perhaps I counted a
little too rapidly and, allowing for that, I judge that the
bands began approximately 2% minutes before totality. They
continued to move over me for only a short time, perhaps ten
seconds, and then they were gone They were faint, thrilling,
ghost-like, but definite enough for me to be sure that I had
seen the shadow bands. . . . . . . “I took my position at
the second sheet to watch for the shadow-bands again. They
began at 15 seconds after totality and to my surprise they
seemed to come from the opposite direction. They were even
fainter than at the beginning and lasted perhaps five seconds.
I moved the second rod until I judged it was parallel to the
crest of the waves.
“At the beginning of totality the bands came from west to
east, moving in the same direction as did the moon's shadow
as it swept across the earth; at the end they moved in the
opposite direction, or so it seemed to me.”
The following account of the same phenomenon as observed
by Dr. A. D. Ross at the same place is taken from the Publica-
tions of the Astronomical Society of the Pacific for Feb.,
1923. -
SHADOW BANDS 57
SHADOW BANDS
I took up a position beside a horizontal white sheet about 1
minute 15 seconds before totality, and was at once conscious
that the phenomenon was present. There was a shimmering
effect over the entire sheet, which at once suggested the shim-
mering of objects seen over a stretch of highly heated ground.
While it was impossible at the time to isolate individual bands
or to note the onward motion (if any), I felt convinced that
the length of the bands (the wave front) lay slightly east of
north to slightly west of south. The distinctness (or rather
indistinctness) of the shadings fluctuated slightly for 15 or
20 seconds, and then I observed that there were narrow dark
lines (about an inch wide) at distances of a foot or so and that
these had an easterly motion.
Petween 1 minute and 40 seconds before totality the bands
underwent a decided development. The narrow dark lines
first acquired a penumbral fringe on each side, and then be-
came reduced in intensity until the dark band was about 6
inches wide and showed only a slight darkening towards the
central part. The bands were always rather indistinct and
unstable in character, but the most persistent type was the
6-inch band described above with a wave-length (crest to
crest) of about 16 inches. The average speed would be over
6 miles per hour.
A plate was exposed 30 seconds before totality, but it was
impossible to record photographically such slight variations in
shade in faint light.
About this time I noticed that the bands were traveling in
groups and I had just made up my mind that there were about
8 in a group, when the next group certainly contained 10 or
58 A HANDBOOK OF SOLAR ECLIPSES
11. The division between two groups would be less than that
produced by omitting one band.
The bands were still visible 20 seconds before totality when
I had to leave for other observations. No observations were
made by me after totality.
It will be noticed that Prof. Chant observed the shadow
bands about two minutes and a quarter before totality was
called but that he saw them “for only a short time, perhaps
ten seconds and then they were gone.” Dr. Ross, on the
other hand did not begin to look for the shadow bands until
“about one minute and fifteen seconds before totality and was
at once conscious that the phenomenon was present’’ and it
was still present twenty seconds before totality when he was
called away. -
&It would appear from tººse observations that the shadowy
bands are affected by the condition of the atmosphere in the
immediate vicinity of the observer. This might account for
the many contradictory reports as to the nature of the shadow
bands that are so generally given. It is certain that the des-
criptions of the shadow bands usually are conflicting which
add to the difficulties of giving a satisfactory explanation of d
Atheir cause and origin/ There are still a number of points
regarding the appearance-of-the-shadow-bands..that need to be
cleared up and photographs of the phenomenon would be very
at the same and different points of observation.
4 Shadow bands have been observed at annular eclipses as
well as before and after total solar elipºy

XII

Aalaak-a-
BATEy's EEADS
A FEw seconds before the beginning of total eclipse the
rapidly dwindling solar crescent, which has become a mere
thread of light by this time, may be seen to break up suddenly
into beads of light, rounded or oblong in shape. The gen-
erally accepted explanation of this odd and beautiful effect,
and—beyond doubt the Correet-erre, is that at this stage of the
eclipse the rough and irregular edge of the moon covers the
edge of the solar disk completely at some points while it just
falls short of covering it at other points. In other words we
see the sunlight coming through the valleys and depressions
at the edge of the moon while the highlands and mountains
cover the solar disk at adjacent points. The same effect will
be seen at the end of the total phase of the eclipse at the oppo-
site or western edge of the sun when the moon first uncoversit.
Baily’s Beads received their name from Sir Francis Baily,
who described this phenomenon in detail after observing it
at the time of the annular eclipse of May 15, 1836, which
passed over the northern part of England and the southern
part of Scotland. His paper on the subject entitled “On a
Remarkable Phenomenon that Occurs in Total and Annular
Eclipses of the Sun” was presented in December of that year
at a meeting of the Royal Astronomical Society, of which he
was then Vice-President. Not only are the beads observed at
annular as well as at total eclipses but they may also be seen
at large partial solar eclipses when the observer is just outside
of the belt of total or annular eclipse. They were seen under
such circumstances by the members of the first American
59
60 A HANDBOOK OF SOLAR ECLIPSES
eclipse expedition stationed near Penobscot in October, 1790,
when this party just failed to get within the belt of totality.
Under fair weather conditions they should be seen at all points
just outside of as well as within the path of the total solar
eclipse, of January 24, 1925, which passes over such-a-thickly
populated-part of this country.
The first mention of the phenomenon later to be known by
the name of Baily’s Beads was by Sir Edmund Halley, of
comet fame, who observed it at the time of the total solar

A eclipse of May 8, 1715, ºnich was the last total solar eclipse
"Visible. †††-'
The first photograph of Baily’s Beads was made at-Ottum-
wa, Iowa, by a section of the Philadelphia Photographic Corps
under Prof. C. F. Hines of Dickinson’s College, Carlisle, Pa.,
at the time of the total solar eclipse of August 7, 1869. The
path of this eclipse crossed the American continent diagonally
from Behring’s Strait to North Carolina, passing over the
states of Iowa, Illinois, Indiana and Kentucky. Later at the
eclipse which occurred on New Year's Day, 1889, the late
Prof. E. E. Barnard of the Yerkes Observatory unintention-
ally photographed Baily's Beads by replacing the cap on his
telescope a second or so too late after taking a final photograph
of the solar corona’ſ recent eclipses the beads have been
observed frequently and occasionally photographed. They may
be considered one of the most interesting features of very
large partial eclipses as well as of total and annular eclipses
of the Sun. Their appearance preceding total eclipse is a
sign that the eclipse will begin within a few seconds while
their appearance at the end of totality is a sign that the
total phase of the eclipse has passed. When they are seen
outside of the path of total eclipse it is a sign that the maxi-
mum obscuration is then occurring at the point of observation.
>}
XIII
THE PASSING OF THE MOON'S SHADOW
IMMEDIATELY preceding the beginning of total eclipse the
approach of the moon’s shadow may be observed to the west-
ward, if the circumstances are favorable, and, less frequent-
ly, its departure eastward at the conclusion of totality. In
general, though, the observer's thoughts are so occupied with
the corona and other phenomena connected with the total
phase of the eclipse that he fails to be on the lookout for the
end of totality and when the appearance of Baily’s Beads and
the first flash of sunlight warns him that the total eclipse is
over the shadow is far away to the eastward. The chances of
seeing it before totality are better as one is apt to be looking
for it then.
There is, however, little chance of seeing the approaching
shadow unless one is stationed at a high elevation above the
surrounding country with a commanding view toward the west,
and in a like manner to observe its departure one must have
a clear view of the eastern landscape. During the few brief
moments that elapse from the first contact of the observer
with the advancing edge of the cone of shadow to his last
contact with the following edge all of the phenomena of total
eclipse will take place and then the shadow will speed onward
and the total eclipse is over in that portion of the shadow
belt. The passage of the shadow from Buffalo, N. Y., to New
Haven, Conn., at the time of the total solar eclipse of January
24, 1925, a distance of over 325 miles, will be accomplished in
six minutes and the entire path of the shadow across the
61
62 A HANDBOOK OF SOLAR ECLIPSES
earth's surface from near Red Lake, Minn., to a point near
the Shetland Islands will be passed over by the shadow-cone
in one hour and forty-three minutes. -
As the shadow travels at an average rate of half a mile a
second it will sweep over the observer like some mighty wall
of darkness engulfing him with unimaginable swiftness. Com-
pared with the velocities to which we are accustomed the speed
with which the moon and its shadow sweep through space is
terrific, though compared with other celestial bodies the moon
is moving at a rather sluggish rate in its orbit. It is because
we have no experience with celestial velocities relative to the
earth close at hand except in the flight of meteors and the
passing of the moon’s shadow that we are so impressed with
this phenomenon. At time of eclipse when the shadow of the
moon sweeps over us we are brought into direct contact with
a tangible presence from space beyond and we feel the immen-
sity of forces over which we have no control. The effect is
awe-inspiring in the extreme. In fact, the passing of the
moon's shadow, if one is fortunate to observe it, will be one
of the most impressive features of the eclipse.
Those who have seen the shadow of the moon approaching
or receding do not in general describe it as black but rather
as blue-black, violet, or brown, or as resembling smoke or a
wall of fog. To some it has appeared “visible in the air” or
‘‘gliding swiftly up over the heavens’’—to others “like a dark
storm on the horizon.” So great is its motion over the
earth’s surface that one has practically no chance to observe
it with any success except at high altitudes. Most observers
refer to its velocity as “frightful” or “terrifying.” Prof.
Langley, who observed the approach of the shadow from
Pike's Peak at the eclipse of July 29, 1878, was impressed
with its distinct appearance. At this high altitude the
PASSING OF THE SHADOW 63
shadow would be expected to appear remarkably clear-cut in
its outline and in fact another observer likened it to “a
rounded ball of darkness with an orange-yellow border”
sweeping over the plains beneath him.
By far the best point of vantage for viewing the passage
of the moon’s shadow is in an aeroplane well above the sur-
face of the earth and at recent eclipses the shadow has
been thus observed and even photographd with some degree
of success. Renewed efforts to photograph the shadow will
doubtless be made at the coming eclipse of January 24, 1925.
The aviator has an unrivaled opportunity to obtain an ex-
tensive view of the shadow track in his immediate vicinity,
both westward and eastward, and so can catch both the first
appearance at the western horizon preceding totality and the
last appearance of the fleeting shadow after totality is over.
In a few instances observers have seen the shadow for
several Seconds preceding or following totality but in gen-
eral it appears with startling suddenness bringing with it the
outflashing glory of the corona and all the attendant phe-
nomena of the total phase of the eclipse.
XIV
THE CHROMOSPHERE AND THE FLASH SPECTRUM
DIRECTLY above the visible surface or “photosphere” of the
sun, as it is called, there exists a comparatively shallow layer
of incandescent gases several thousand miles in depth, known
as the chromosphere. At some total eclipses when the moon
is so distant that it barely covers the photosphere and leaves
the solar atmosphere exposed, the chromosphere may be seen
as a narrow ring of a deep rose color contrasting beautifully
with the black body of the moon and the pearly radiance of
the corona. Generally, however, the moon covers the chro-
mosphere as well as the photosphere and only the Scarlet
flames of the solar prominences, of which we will speak later,
may be seen rising from the hidden chromosphere. -
The beautiful rosy tinge of the chromosphere is due to the
presence of incandescent hydrogen gas which with helium and
calcium may be regarded as the permanent gases that are al-
ways present in the chromosphere, and that appear at high as
well as at low altitudes. -
In the lower, denser layers of the chromosphere, on the
other hand, will be found the incandescent vapors of most
of the chemical elements that are found on our own planet,
including iron, sodium, magnesium, barium, etc. They are
often spoken of as the metallic vapors and they are the same
elements that are found in the sun itself. This lower layer
of the chromosphere is known as the “reversing layer,” for a
reason that will soon be evident, and in it originates the “flash
64
CHROMOSPHERE AND FLASH SPECTRUM 65
spectrum’’ first observed by Prof. C. A. Young of Princeton,
who discovered it at the Spanish eclipse of 1870.
If the light of the sun is broken up into spectrum colors by
means of a diffraction grating, which consists of a number of
lines ruled extremely close together, or by means of a glass
prism or train of prisms, that is the essential part of the spec-
troscope, one will observe a number of fine, dark lines on a
continuous background of variegated color running from the
red to the violet. These dark lines are the Frauenhofer lines
or the absorption lines of the solar spectrum. They have
their origin in the cooler gases that lie above the photosphere
in the reversing layer and they appear dark only by contrast
with the more brilliant and hotter background against which
they appear.
Now as the moon advances over the photosphere there will
come a time, simultaneous with the disappearance of Baily’s
Beads, when the light from the photosphere is shut off while
the chromosphere still remains visible. At this instant if one
has a spectroscope pointed at the disappearing sun it will be
noticed that the luminous background of the solar spectrum
suddenly disappears leaving only darkness while at the same
instant the formerly dark lines of the solar spectrum Sud-
denly flash forth as a magnificent series of thousands of bril-
liant lines. As this phenomenon represents a reversing of
the solar spectrum, the luminous background of color becom-
ing dark and the dark Frauenhofer lines becoming bright, the
layer of the chromosphere that produces these lines is referred
to as the “reversing layer.” As its depth is scarcely five
hundred miles the moon covers it in a single second. So
the flash spectrum is as its name suggests a mere flash of
bright lines, gone almost as soon as it is seen.
The appearance of the flash spectrum is an indication of
66 A HANDBOOK OF SOLAR ECLIPSES
the beginning of total eclipse and its reappearance imme-
diately preceding the uncovering of the photosphere by the
moon is a sign that the end of totality is at hand.
Observations of the flash spectrum are of great scientific
value and are always included in the program of observations
of eclipse expeditions. They give the astronomer a clue as to
the condition of this lower solar atmosphere, the nature of
the elements of which it consists and its dependence upon
other solar phenomena. The sun is to us the very source of
life itself. So every bit of information that may be added
to our store of knowledge concerning it is specially to be de-
sired, particularly as there is still so much that is unexplained
regarding the great cyclic changes in solar activity that are
continually taking place.
The flash spectrum cannot be observed without the aid of
a spectroscope or some device for producing the solar spec-
trum. If one can procure a plane diffraction grating, how-
ever, it is possible to observe the flash spectrum with no addi-
tional equipment except a pair of binoculars. This method
of observing the flash spectrum and recording the beginning
of total eclipse was devised by Dr. L. E. Jewell, formerly of
the U. S. Naval Observatory, now with the Research Depart-
ment of the Eastman Kodak Co. and was used first in Sumatra
at the total solar eclipse of May 18, 1901. By placing a dark
glass before one barrel of the binocular and a small plane
grating before the other it is possible to observe the disappear-
ing crescent with one eye and to record the appearance of the -
flash spectrum with the other. The flash spectrum was ob-
served beautifully in this way at Sawah Loento, Sumatra, by
one of the three eclipse parties of the U. S. Naval Observatory
through thin clouds at the conclusion of totality. At the be-
CHROMOSPHERE AND FLASH SPECTRUM 67
ginning of totality the clouds were so dense that no observa-
tions were possible.
If the reader has an ambition to photograph the flash spec-
trum with a modest equipment he will find an interesting de-
scription of how this can be accomplished in an article on the
coming eclipse of January 24, 1925, in Popular Astronomy
for May, 1924, by E. A. Fath; also in the same number a
method of photographing the corona with spectacle lenses by
Mr. J. H. Worthington. With the kind of instrument de-
scribed for photographing the flash, Dr. H. C. Wilson, editor
of Popular Astronomy, obtained a photograph of the flash
spectrum in Colorado at the total solar eclipse of June 8,
1918, upon which 1008 lines could be measured.
XV
TEHE SOLAR PROMINENCES
A BEAUTIFUL feature of most total solar eclipses are the
scarlet flames of incandescent hydrogen, mingled with helium
and calcium, that rise to heights of thousands of miles
above the surface of the sun at many points and that are now
known by the name of solar prominences.
Earlier observers of solar eclipses referred generally to
the prominences as the “red flames.” The first recorded in-
stance of observation of this phenomenon was by a Captain
Stannyan, who saw them at the total eclipse of 1706 at Berne,
Switzerland. Writing a description of his observations of the
eclipse to the astronomer Flamsteed, he says, in reference to
this phenomenon, “— his (the sun's) getting out of his
eclipse was preceded by a blood-red streak of light from its
left limb, which continued not longer than six or seven seconds
& 4
of time.”
At the famous eclipse of May 3, 1715, which was the last
total solar eclipse visible in London, the astronomer Halley
observed ‘‘dusky but strong red light which seemed to color
the dark edge of the moon.” From that time on in records of
eclipse observations there are a number of references to the
‘‘red flames’’ that appeared during totality.
It now seems strange, when the prominences are a common
phenomenon observable by means of the spectroscope in broad
daylight as well as during total solar eclipse, that not until
the year 1860 was it definitely proven that the “protuber-
ances,’’ as they were then generally called, were associated
68 *
THE SOLAR PROMINENCES 69
with the sun instead of the moon. It appeared to be a common
idea up to that time that they were a part either of the atmos-
phere or surface of the moon. During the eclipse of 1860
visible in the United States and Spain, the observations
proved beyond the shadow of a doubt that the protuberances
were a solar phenomenon. As the moon advanced over the
disk of the sun it was noted that it gradually covered and
uncovered the “proturberances,” a name which after that was
used less and less until it was finally superseded by the more
suitable one of “solar prominences.” The application of the
spectroscope to the study of celestial phenomena about that
time, which ushered in the present wonderful age of the
“new astronomy,” soon revealed the fact that the scarlet color
of the solar prominences is due to the presence of vapors of
incandescent hydrogen, though lines of calcium were also
found to be present in the spectrum of the prominences and a
strong, yellow line at first thought to be due to sodium but
soon found to be due to the presence of a new element, helium.
A wonderful forward step in the study of the solar promi-
nences was made immediately following the total solar eclipse
of August 18, 1868, which was observed in India and the
Malay Peninsula for over five and a half minutes, the longest
eclipse of which scientific observations had been made up
to that time. Here were eclipse expeditions from England,
France, Spain and Germany. So great was the brilliancy of
the prominences at that eclipse that the French astronomer
Janssen, who observed them with the greatest success at Gun-
teer, during the eclipse, decided to attempt to observe them
in broad daylight after the eclipse. This he accomplished
by using a spectroscope of wide dispersion which weakened
the continuous spectrum background produced by the re-
flection of sunlight by particles in the earth’s atmosphere
70 A HANDBOOK OF SOLAR ECLIPSES
while it left unaffected in intensity the monochromatic light
of the scarlet prominences.
In the meantime Lockyer, the English astronomer, was
working on the same problem and attained success at prac-
tically the same time. Janssen had continued his observations
of the prominences for some days following the eclipse but de-
layed in communicating his results to the French Academy of
Sciences so at the meeting that fall two papers were read
on observing the solar prominences in daylight, one by Lock-
yer and the other by Janssen, and a gold medal was struck
by the French government in honor of the brilliant discovery
made independently by the two astronomers.
Many attempts have been made also to photograph the
solar corona in broad daylight but owing to the extreme faint.
ness of its light all attempts have so far been in vain.
At total eclipses that occur during the sunspot maximum
period the solar prominences are almost invariably extremely
beautiful and intricate in form and conspicuously visible even
to the naked eye. Sometimes they are found associated with
sunspots and sometimes they occur entirely independent of
them but there appears to be some close connection between the
coronal streamers and the solar prominences. “Hooded” or
“arched” prominences, for example, are frequently observed
during the sunspot maximum periods in which coronal
streamers seem to form a hood or arch over the prominences.
Also long coronal streams seem at times to have their origin
in the vicinity of conspicuous prominences. The connection
between the coronal streamers and the prominences is one of
the most interesting of the problems that the scientific observer
of Solar phenomena has to solve. It is believed that streams
of electrons affecting the earth's magnetism and causing auror-
al displays may be shot off from the sun in the vicinity of
Disturbance on south-west limb of sun. The arches are immediately over a large sunspot. Note large solar
prominence to right of arches. Photograph taken by Sproul Observatory Expedition, Mexico, September 10,
1923.

THE SOLAR PROMINENCES 71.
prominences as well as from sunspot regions. There are
many solar problems still awaiting solution that may have
a very direct bearing on magnetic and electric phenomena of
the earth’s atmosphere, including wireless and telegraphic
communication. It is never known when some apparently
abstract piece of information gleaned from scientific observa-
tions at times of total eclipses of the sun may have a very im-
portant association with terrestrial affairs. It may be well
to recall here that the yellow line in the spectrum of helium
was first observed in solar prominences before it was seen on
earth; that in the year 1868 Lockyer gave this name of
“helium” to the hypothetical element that he observed in the
spectrum of the sun.
Not until twenty-seven years later did Ramsey find the same
line in the spectrum of an inert gas obtained from the mineral
clevite. Lockyer's helium discovered in the solar spectrum
in 1868 and the new gas found on the earth by Ramsay in
1895 were the same.
Prominences are of two classes, eruptive and quiescent.
The quiescent prominences may persist practically in the same
form for days at a time, floating above and often apparently
detached from the solar surface, like terrestrial clouds. The
eruptive prominences assume strange and rapidly changing
forms. The entire aspect of an eruptive solar prominence
may be entirely changed in a brief fifteen or twenty minutes.
The height attained by prominences of both varieties is some-
times enormous. Though exceptional,—altitudes of 200,000
to 500,000 miles have been recorded. A record breaking
prominence of a few years ago attained an altitude of over
500,000 miles, or more than half of the diameter of the sun.
In general though the prominences do not exceed 20,000 miles
in height, particularly during sunspot minimum periods.
72 A HANDBOOK OF SOLAR ECLIPSES
The total solar eclipse of June 8, 1918, occurred during a
sunspot maximum period and the prominences that were so
conspicuously visible during totality were particularly beauti-
ful and interesting in form. The photographs also indicated
that the prominences were affected by strong currents in the
solar atmosphere blowing toward the solar equator. Two
striking prominences seen at this eclipse were the Heliosaurus
prominence, so named from its resemblance to the skeleton of
some prehistoric animal, and the Eagle prominence, which
resembled an eagle alighting on a lofty mountain. They
remind one of the strange forms that are seen in fancy in
summer clouds. Yet compared to the ‘‘skeleton” prominence,
estimated to be at least 40,000 miles in height, our whole earth
with its diameter of 8,000 miles would be a rather insignificant
object. . *
In sharp contrast to the 1918 eclipse with its strikingly
beautiful prominences is the eclipse of September 21, 1922, ob-
served in Australia, at the sunspot minimum period. Ob-
servers found that at this eclipse not a single prominence was
visible to the naked eye. -
As the Sunspot minimum period is now well past and solar
activity is setting in once more it is probable that prominences
will again be visible at the eclipse of January 24, 1925, though
not as conspicuously as at the 1918 eclipse.
Past observations of eclipses show that in some instances
the prominences have been visible for as long as five or six
minutes before and after the total phase of the eclipse though
in general they are seen only during totality.
-
Expedition at Matheson,
‘‘Heliosaurus” and other prominences photographed by Yerkes Observatory Eclipse
Colorado, June 8, 1918.

XVI
THE SOLAR CORONA
§ THE glory of a total solar eclipse lies in its wronº It is
the phenomenon that is of the greatest interest to the spectator
and of the greatest scientific value to the astronomer, who
seeks to solve its mystery.
The corona appears only when the light of the sun is com-N
pletely blotted out, simultaneously with the appearance of the -
flash spectrum at the beginning of total eclipse, and it dis-
appears with appearance of Baily’s Beads at the end of
totality. So faint is its light, scarcely exceeding that of the
full moon at best, and usually considerably less, that all
of the numerous attempts that have been made to observe it
without a total eclipse have so far failed.
In the clear, rare air of Pike's Peak during the total solar
eclipse of 1878, Prof. Simon Newcomb and Prof. Langley in-
dependently traced the delicate coronal streamers to the tre.
mendous distance of twelve solar diameters or about eleven
million miles from the sun, and held them steadily in view
for more than four minutes after the end of totality, but this
was exceptional. It is probable that in airplanes at high
elevations above the earth’s surface much more detail would
be seen with the naked eye than at sea level but as the short-
est exposures used in photographing the corona are a second
or over while exposures of thirty seconds or more with power-
ful cameras are common, there is little, if any, chance of at-
taining success in photographing any detailed structure in
the corona from airplanes. Amateurs who wish to attempt
73
74. A HANDBOOK OF SOLAR ECLIPSEs
\
º
to photograph the corona might attain some success with small
cameras with an exposure of about five seconds or by using a
camera attachment with a small telescope on an equatorial
mounting.
The wealth of delicate tracery and detail in the structure of
the corona that the long exposure photographic plates reveal
cannot be appreciated from looking at the photographs for
much of this detail is lost in the printing and more in the
reproductions. Neither can one appreciate the exquisite’
pearly radiance of the coronal light as it appears to the ob-
server in striking contrast to the vivid scarlet of the promi-
nences and the forbidding darkness of the moon.
The details of structure in the form of the corona are never
the same in any two eclipses though there is a general change
in type with the eleven-year sunspot cycle that is so marked
that the astronomer can predict in advance the form of corona
if he knows at what part of the sunspot cycle it will occur.
At and near the time of maximum spottedness of the sun,
when the solar activity is greatest, when the sun is hardly ever
free from spots and when solar prominences are most con-
spicuous the solar corona is evenly developed all around the
solar surface and is more than normally bright. At the sun-
spot minimum period, when the sun is often free from spots
for days at a time and when the prominences are few and
inconspicuous and generally confined to the sunspot zones
within a belt forty degrees wide on either side of the solar
equator, then there appear short, bushy coronal streamers sep-
arating sharply to eastward and westward above the solar
poles, like the lines of force emanating from the ends of a
bar magnet, while in equatorial regions of the sun long cor-
onal streamers extend to distances of several solar diameters
or several million miles from the sun. The corona is then
THE SOLAR CORONA - 75
much fainter in general, than at sunspot maximum and few
if any conspicuous prominences are visible to the naked eye.
At times intermediate between sunspot maximum and mini-
mum the corona is intermediate in type, being roughly rectan-
gular in shape. The United States eclipse of June 8, 1918,
which occurred during a sunspot maximum period, was noted
for the number and beauty of its prominences and for the
brightness and intricacy in structure of its corona, which,
true to type, was evenly developed around the solar disk, the
short bushy polar streamers being concealed by the longer
superimposed streamers. -
The eclipse observed in Australia September 21, 1922,
occurred, on the other hand, very near the time of sunspot
minimum and the corona was very inferior in brightness to the
1918 eclipse: no prominences were visible to the naked eye
while those revealed telescopically were small and few in
number. This eclipse also was true to type with the short
bushy polar streamers parting sharply over the solar axis of
rotation, which coincides closely with the sun's magnetic axis.
The long equatorial streamers were also clearly in evidence.
The relative smallness and faintness of the corona showed
that the sun was in a remarkably quiescent state. The eclipse
of September 10, 1923, observed in Mexico by the Sproul ex-
pdition of Swarthmore College and by the Mexican
National Observatory expedition was brighter and showed
signs of a gradually awakening solar activity. Prominences
were plainly visible in small telescopes but not to the naked
eye and were not of their usual vivid scarlet, being described
as whitish in appearance. The polar streamers at both poles
were very long and well-defined but faint, the north-polar
streamers being traced to a distance of over half the diameter
of the sun, or something like five hundred thousand miles from
76 A HANDBOOK OF SOLAR ECLIPSES
the sun. They were longer but less bright than those around
the southern pole. The corona on the eastern side of the sun
was very simple in structure although three large promin-
ences of the quiescent variety were visible on that side. The
corona on the southwestern side was not nearly as simple,
however, being even more complex in that particular region
than the corona of 1918.
It may be predicted that the corona of the coming eclipse
of January, 1925, will be brighter and more evenly developed
than the last eclipse and prominences may be expected to be
in evidence,—though this is to some extent a matter of chance.
As the period is intermediate between the sunspot maximum
and minimum the corona should be of the rectangular or
intermediate type. As the sunspot minimum was passed in
the spring of 1923, or possibly earlier, the maximum should
not occur until 1928, but the rise to maximum spottedness is
much more rapid than the decline to minimum. There are
now signs that the new cycle of solar activity is well started.
It has often been observed that the coronal streamers have
a tendency to form conspicuous arches or “hoods” over crup-
tive prominences. The seat of coronal disturbances, in fact,
often seems to lie in the vicinity of the prominences, and
there seems to be a close connection between the prominences
and the corona. Yet the lines of hydrogen and calcium gas
that are conspicuously present in the prominences are never
found in the spectrum of the corona. There appears to be,
in general, no noticeable connection between groups of sun-
spots and coronal streamers, such as exists between promin-
ences and corona. -
-The origin and the nature of the solar corona and the reason
for its change of form with the sunspot cycle are tº
but it is believed the astronomer is much nearer the solution
THE SOLAR CORONA 77
of these problems than he was a few years ago. {It is certain,
for instance, that the corona consists partly of minute par-
ticles of matter that scatter and reflect the light of the sun,
particles that are probably driven off from the sun itself by
light pressure and in other ways. In addition there is prob-
ably a photoelectric effect, that accounts for much of the
luminosity of the corona, produced by the passage of streams
of electrons through the rare gases of which it consists just
as the light of the aurora is a photoelectric effect produced by
a bombardment of the rare gases of the earth's upper atmos-
phere by streams of electrons from the sun. The spectroscope
shows that there are a number of bright lines in the spectrum
of the corona, which indicates that it shines partly by its own
light. A conspicuous bright line in the green has been
attributed to an unknown element, coronium, that has been
found nowhere except in the corona. ( There is also an un-
known line in the red that is very conspicuous at times and,
in addition, a number of other lines of unknown origin.
It is believed that these may be lines, not of unknown ele-
ments, but of some familiar elements electrically excited.
It is possible that the bright lines of the unknown nebulium in
the rare gaseous nebulas are produced in an analogous way
and when the source of the coronium rays is found the
cause of the presence of nebulium in the nebulas may be ex-
plained also. It is probable too that other suns as well as
our own have their coronas but that they are masked by the
far more brilliant radiations of the stars themselves, just as
is the case with our own sun, except during eclipse.
Talso, it may be that much of the intricate tracery of the cor-
onal streamers and complex structure that is caught by the
photographic plates and the eye of the observer during totality

78 A HANDBOOK OF SOLAR ECLIPSES
results from the fact that the sun like the earth is a magnet
and is surrounded by a strong megnetic field.
It is still unknown whether or not the corona rotates with
the sun though efforts have been made and are still being made
to settle this question by observations made at each total
eclipse. Also efforts have been made for some time to de-
termine whether rapid changes in coronal form take place,
during the time that elapses between the observation of the
eclipse at points a considerable distance apart in the shadow
path. So far it has either been impossible to obtain photo-
graphs for comparison at the widely separated stations or else
only negative results have been obtained. No light can be
shed on this problem in the coming eclipse of 1925 as all avail-
able stations are only a few minutes apart in time.
It is probable that when the radiations of the corona are
understood the whole problem of solar radiation and the
cause of the sunspot cycle will be understood. So the problem
of the cause and nature of the coronal radiations and the
reason for the change in form of the corona with the sunspot
cycle are the greatest of eclipse problems. So far no way
to approach their solution has been found except through ob-
servation of total eclipses of the sun. Partial solar eclipses
are of course useless for this purpose as well as the annular
type of eclipse. As the problem of solar radiation is so
vitally associated with electric and magnetic changes on the
earth as well as meteorological changes its solution is one of
great practical value. Radio and telegraphic communica-
tions, temperature and rainfall on earth may all be affected
by the same change in solar activity that produces a sunspot,
an eruptive prominence, a stream of electrons or a change of
structure in the corona. It is the cause of important solar
changes and their effects that the astronomer seeks to discover
THE SOLAR CORONA 79
through the observation of the corona during a total Solar
eclipse. The time granted for the solution of this problem
is pitifully small, possibly two minutes this year or three or
four minutes, or none, next year.
From the time when photography was first applied to the
observation of the solar corona, in 1860, up to the present
day the total time available for the study of the corona has
probably totaled less than a single hour, so it is not to be won-
dered at that our knowledge of the nature of the coronal
radiations has progressed slowly. There has been accumul-
ated by this time, however, a fine series of coronal photographs
secured at practically all phases of the sunspot cycle and it is
only a matter of a few years at the most before these scien-
tific records of eclipses, secured in some instances by expedi-
tions sent to strange and far-away corners of the earth, should
begin to bear fruit. It is possible that valuable and far-
reaching discoveries regarding the nature of solar energy may
be forthcoming in the near future as a result of the scientific
observations of total solar eclipses, though this progress is
necessarily so discouragingly slow. Prof. W. W. Campbell,
Director of the Lick Observatory, who has probably observed
more total solar eclipses than any other man living today, has
estimated that all the time that he has been granted for ob-
servations of the corona and other phenomena of totality
has totaled less than one half hour ! The astronomer who
stays at home is fortunate if he sees one solar corona in a
life time.
XVII
TEIE ECLIPSE PAINTING
THE first, and so far the only painting of a total eclipse
of the sun, was made of the eclipse of June 8, 1918, by Mr.
Howard Russell Butler, the well-known portrait painter, who
with this object in view became a member of the U. S. Naval
Observatory expedition to Baker, Oregon.
The idea of an eclipse painting was conceived by Mr.
Edward D. Adams, of New York, founder of the Ernest
Kempton Adams fellowship awarded each year by Columbia
University for researches in the field of pure science. It was
Mr. Adams’ desire to secure, by means of photography, draw-
ing or painting, a reproduction of an eclipse that would be
true both as to color and form.
Unfortunately not only are the exquisitely contrasting color
effects of pearly corona, dusky moon and rose-tinted promin-
ences lacking in the photographs, but much of coronal detail
is lost in the reproduction because of the great difference in
brightness between the inner and outer corona. An exposure
long enough to bring out the faint outlying coronal extensions
is too long for the far more brilliant inner corona which ap-
pears as a glare of light lacking in deatil as a result of over-
exposure. The only successful method of reproducing coronal
detail has been by means of composite drawings from a num-
ber of negatives taken with different exposures and different
cameras. By this means all the detail in both the inner and
the outer corona can be reproduced. Yet these drawings do
80
The Corona of June 8, 1918. Photograph taken by U. S. Naval
at Baker, Oregon, with camera of 65-feet focal length.
Observatory Expedition,

THE ECLIPSE PAINTING t 81
not reproduce the superb color effects of the eclipse and so
Mr. Adams undertook to find the man who could both draw
and paint the corona and prominences. That he was highly
successful in his search all will agree who have had the oppor-
tunity to see the painting of the total solar eclipse of June 8,
1818. -
Three paintings of the eclipse were made by Mr. Butler,
the first immediately after the eclipse, the second on the fol-
lowing day and the third after all data had been secured. One
of these paintings was presented to the American Museum of
Natural History in New York by Mr. Edward D. Adams, and
may be seen in the Astronomical Room, which is kept darkened
except for the indirect lighting of the painting of the eclipse.
A description of the methods used in painting the eclipse
and the manner in which it was observed by him is given by
Mr. Butler in Natural History, 19, 244-271, 1919, published by
the American Museum of Natural History.
The usual time that he asks for in painting a portrait, Mr.
Butler states, is ten or twelve sittings of two hours each. In
the painting of the eclipse he found that he was required to
render his subject in 112 seconds! It was, moreover, the first
total solar eclipse that he had ever seen.
All those who have seen both the painting of the corona by
Mr. Butler and the original agree that the reproduction is
wonderfully accurate both in color and in form. Happily too
the eclipse of 1918, which occurred at the sunspot maximum
period, was remarkably rich in coloring, the prominences, in
particular, being unusually brilliant and conspicuous in size
and shape. Several of the more noticeable prominences were,
in addition, “hooded” or arched over with series of coronal
streamers producing a most beautiful and curious effect.
82 A HANDBOOK OF SOLAR ECLIPSES
It was peculiarly fitting that this most resplendent of re-
cent eclipses should have been the one chosen for reproduction
in colors. So skillfully is Mr. Butler’s painting of the eclipse
executed that it deserves to be classed high among the con-
tributions to science that are a product of eclipse expeditions.
XVIII
HOW TO WIEW THE ECLIPSE
NoTHING is essential for observing a total eclipse of the
sun successfully except a good pair of eyes, though a pair of
binoculars or opera glasses might be used to advantage in ob-
serving the solar prominences and the corona during the total
phase of the eclipse. These should be adjusted and focussed
in advance, however, for the moments of totality are short
and precious and if you cannot make use of the glasses quickly
and easily it would be wiser to dispense with them altogether.
In no case should binoculars be used during the partial phase
of the eclipse without taking the precaution to fasten a piece
of dark or colored glass over the ends to protect the eyes.
The flash spectrum cannot be seen unless one has some
means of forming the solar spectrum as explained in Chapter
XIV but aside from this the general observer has just as good
a chance of seeing all the principal features of the eclipse as
the scientific observer, in fact, a better chance, for the
astronomer who is engaged in making scientific observations
during the total phase of the eclipse or in photographing the
corona must give his undivided attention to his instrument
and can at most spare only a hurried glance for the scenic
Splendors of the eclipse.
Though the amateur has the best of it when it comes to
opportunities for observing the various features of the eclipse
the chances are that he will observe next to nothing unless he
knows in advance what to look for and when to look for it.
The wise man will plan to make the most of his opportunities.
83
84 A HANDBOOK OF SOLAR ECLIPSES
It is well not to strain or fatigue the eyes by gazing need-
lessly at the sun during the partial phase of the eclipse even
when the precaution of using dark glasses is taken. It will
be an hour or so from the time of “first contact,” when the
partial phase of the eclipse begins, up to the time when the
thin solar crescent breaks up into Baily’s Beads and the
corona flashes forth in all its ethereal splendor. During the
earlier part of this period there is nothing of scientific interest
and little of general interest to observe, aside from the record-
ing of the time of first contact of the rims of sun and moon
and the recognition of the fact that the eclipse is “on.”
When the magnitude of the eclipse has become as great as
eighty percent or so the visible part of the sun will have be-
come decidedly crescent shaped and the light will have dimin-
ished to such an extent that the landscape will begin to take
on a strange aspect, as if viewed through yellow glasses. Look
now for crescent shaped images of the sun formed by passing
its light through very small openings or through lenses. When
the leaves are on the trees the small openings between the
leaves act as tiny lenses casting small images of the eclipse
on the ground,-numberless little crescents with their horns
turned in a direction opposite to that of the crescent sun above.
This interesting phenomenon produced by the leaves cannot
of course be observed in a winter eclipse and we must look
elsewhere for our crescent shaped images of the sun or find
a means of producing them for ourselves.
By this time it may be noticed that birds and animals are
displaying a strange uneasiness and in the past this uneasiness
was by no means confined to animals alone. One of the
greatest services of astronomers to mankind has been to free
the more civilized nations of the world from the terror and
panic that always attended the appearance of such phenomena
HOW TO WIEW TEIE ECLIPSE 85
as eclipses and comets. Even at the present time this fear
of eclipses is very general among the ignorant classes in China
and in India and among uncivilized races in many lands. The
ringing of gongs and the beating of drums is still common
in Asia during lunar as well as solar eclipses, where the belief
that a dragon with dark claws is attempting to devour the sun
or moon still persists.
When the solar crescent narrows to a thin line look for the
shadow bands. They often appear as early as five minutes
before the total eclipse begins. All observers who are with-
in the path of total eclipse are urged to make observations of
shadow bands as outlined in Chapter XI. Here is a chance
for everyone to do his little bit for science and if one can
succeed in photographing this phenomenon he will accomplish
a feat that no one has succeeded in accomplishing up to the
present time, though many attempts have been made at past
eclipses. Also, do not forget to look for the shadow bands
directly after as well as before the total eclipse.
About this time or even earlier look for the appearance of
the brighter planets. Venus, Mercury and Jupiter appear
in a close group some distance to the southwest of the sun
during the total eclipse of January 24, 1925. Venus will
appear before any of the other planets or stars because it is
by far the brightest, next Jupiter will be seen, then Mercury
close to Venus and, to the northwest of the sun, the first
magnitude star, Altair, and still more distant in the same
general direction Vega, one of the brightest stars in the
heavens.
Within the last few minutes preceding the beginning of
total eclipse there is plenty to occupy the attention of the
observer. The landscape has now taken on a strange hue.
The appearance of the shadow bands adds to the unearthly
86 A HANDBOOK OF SOLAR ECLIPSES
effect. The solar crescent is now narrowing to a mere line.
Be on the watch for the appearance of Baily’s Beads. It is
said that at some eclipses they are not observed. At the same
time be on the lookout for the approach of the shadow from
the west if you are at some elevation above the surrounding
country and in a favorable position to observe its approach.
It will appear as Baily’s Beads disappear and a second later
you will be gazing upon the unrivalled beauty of the solar
corona with all of its delicate tracery and intricate detail.
Note its color and brightness and general form; also estimate
the extent of its equatorial streamers, using the diameter of
the Sun or moon for comparison. Are there pronounced polar
brushes and long equatorial extensions to the corona, the
sunspot minimum type—or are the polar brushes absent and
the extension of the corona fairly regular in all directions?
Are there prominences visible to the naked eye and what is
their color? Are they deep scarlet, rosy hued or whitish? Do
the coronal streamers form arches or hoods over the promi-
nences? Make a rapid sketch of the form of the corona and
the location of the principal prominences. Take particular
pains to do this if no astronomical expeditions are located in
your vicinity for there is a chance that you may be favored
with fair weather and the astronomers not, in which case your
little sketch may be of value. Photographs of the corona
may be attempted with ordinary cameras with a time exposure
of about five seconds but much detail cannot be expected to
appear on these photographs. Note the appearance of the
moon. Is it inky black or grayish? Does it stand out in
relief as a huge globe Observe the beautiful contrast in
color between the pearly radiance of the corona, the rose-
colored prominences and the dusky moon. Note the degree of
darkness of the eclipse. Is it possible to read or see the hands
HOW TO WIEW THE ECLIPSE 87
of your watch? It has been found that the degree of dark-
ness varies greatly at different eclipses.
It is a good idea to form a small observing party with a
number of friends each agreeing to give particular attention
to some one phase of the eclipse, shadow bands, prominences,
sketches or photographs of the corona, etc., while observing
more generally all phenomena so far as possible. In this
way some observations of real scientific value may be obtained
while in any case the general observer will be satisfied that he
has made the most of a rare opportunity to witness a spectacle
such as most of us do not have the privilege of seeing once in
a life time.
The following interesting description of the Australian
eclipse of September 21, 1922, as it appeared to a layman, is
taken from a diary of the event written by S. Elliott Napier
and published in the Sydney Mail. The place of observation
was the small town of Goondiwindi in New South Wales.
We quote it as giving an excellent idea of what any observer
of a total solar eclipse may expect to see in general. As
regards the failure to see any prominences we would recall
that this eclipse occurred at the sunspot minimum period when
the sun was in an unusually quiet state and, according to the
report of the Lick-Crocker Expedition, which observed the
same eclipse at Wallal on the western coast of Australia, no
prominences were visible to the naked eye at this eclipse.
º
TEIE GREAT DAY
Thursday, September 21, 9 a.m.—Brilliantly fine. Not a
cloud. SW wind. Cold night. Town crowded at an early
hour—10 a. m. Governor (Sir Matthew Nathan), who arrived
at midnight, given civic reception. The eclipse is now under
vice-regal patronage, and the last chance of a failure is there-
88 A HANDBOOK OF SOLAR ECLIPSES
by removed. The scientists’ camps bustling like disturbed
ant-heaps—each lot getting its last details overlooked and its -
last button polished. I am to have a corner in the sacred pre-
serve and a star-chart, and my job is to locate the stars and
planets that become visible and the respective times of their
appearance as closely as possible. A sheet to “catch” the
shadow bands has been laid on the ground near the fence,
and two cameras trained on it. These are to be worked by
Mr. Edwin Fletcher (solicitor, of Goondiwindi, to whose kind-
ness the visitors in the town generally, including myself in
particular, are deeply indebted), and his daughter. They are
instructed in their duties by Mr. Booth, the spectroscope king,
who is a genial person with a habit of saying “Quite—quite l’’
when he means to emphasize his affirmations. Under the ex-
citement of the occasion I hear him firing a feu-de-joie of
“Quites” that would do credit to Mark Twain's echo. All
who can are asked to watch for and note as particularly as
possible the direction in which the shadow bands move, their
approximate thickness, the distance between them, their rate
of speed, and when they commence and how long they last.
2 p.m.—People everywhere: many of them already look-
ing at the sun through glasses—especially in the bars; the
town very lively with cars—I count 47 in the main street as
I go to “stations.” The clouds have all disappeared. Wind
very fresh from SW causes the coelostats which serve the var-
ious telescopes to tremble.
2.30p. m.—Everybody reported for duty; all watches syn-
chronized; everybody ready—even Father Pigot has a moment
to sit down and murmur soothing words to his beloved pyran-
ometer. I understand that during a slight altercation in its
vicinity between two of the scientists this morning it recorded
a heat rediation that nearly wrecked the galvanometer. My
HOW TO WIEW TEIE ECLIPSE 89
notes from now on must necessarily be brief—the hour ap-
proaches. A special theodolite telescope has been set up for
the Governor, who is to arrive shortly—and by an arrange-
ment of tinted glasses it shows the sun as a disc of blue. The
“blue moon” is familiar; but this is the first sun of that shade
I have met with. A slight smoke from the railway pumping
plant hazes the sky a bit towards the west.
3 p.m.—A little less than 6 minutes to go before “first con-
tact.” Conditions perfect.
3:5.58.-Mr. Nangle, looking through the W. R. theodolite,
announces “first contact”; in a few seconds everybody notes
it.
3:6.50.-Cusp showing up distinctly in all telescopes. The
eclipse is “up to time.”
3.18—Great excitement The Governor, applying for ad-
mission at the back gate, has been thrust with ignominy away.
Will we all be arrested for lese majeste?
3.25.-All well again. The Governor is a sport, and—
went round to the front and was admitted. He goes to his
little telescope, and everybody is happy. About a quarter of
the sun is now obscured. I try to see the ‘‘pictures of the
eclipse” thrown on the ground by the light filtering through
the leaves. Unsuccessful—probably, the trees being peppers,
the foliage is unsuitable.
3.47.-Cocks crowing and birds flying about in some alarm;
distinct failure of light and fall in temperature; about half
SUlD1, .
3.52.-Venus visible (probably earlier than this—but this
is the first moment I saw her.) Peculiar deep blue tint assumed
by western sky. The shadows of all objects are taking on
fantastic edgings and distortions.
90 A HANDBOOK OF SOLAR ECLIPSES
4:8.—Sun now a mere crescent; fall in temperature; slight
breeze springs up; three minutes to go before totality.
4:9-Jupiter visible; the light grows more and more weird.
There is little talk, except in whispers.
4:10.-Mercury visible; Saturn visible; and, looking back
towards east, I see Mars quite plainly. He has evidently been
visible for some time. The breeze has died down to a complete
calm. One minute to go. “Shadow bands” clearly visible
about half a minute later.
4:11.40.-A sudden flash, and the sun disappears, Time-
keeper calls “Go!” The black silhouette of the moon is
suspended against the corona. Latter of a beautiful silvery
glow. I see no colors, neither do I observe any “prominences”
or “Baily’s Beads.” I draw a rough sketch of the corona
(which agrees fairly well on subsequent comparison with
those of other observers, showing four extensions—two above,
two below—the left-hand lower one being the largest of the
four, and the right-hand lower one having a serrated terminal
edge). Black prominence on moon. Not so dark as I ex-
pected, but light unlike anything I ever saw—neither moon-
light nor twilight—more like “seeing through a glass darkly”
than anything else. I notice Spica between Mercury and
Jupiter; also B. Leonis and—I think—B. Virginis, quite close
to the sun; one of the “Einstein’’ stars; a glance round to the
south shows three of the stars of the Cross, also both pointers.
Finally, I note Arcturus to the north. The most notable
features of totality: the eerie appearance of the dead-black
moon against the radiant corona—a veritable ‘‘study in black
and silver’’—the incomparable beauty of the corona itself—
its sudden appearance, and the “flash” which heralds the be-
ginning and end of totality. Also the extraordinary weird-
ness of the light. I notice a golden—almost reddish—glow
HOW TO WIEW THE ECLIPSE 91
round the horizon (probably the reflected light from the un-
shadowed portion of the earth, 75 miles away). Very little
said by anyone; but of the awesome and wonderful impression
made there can be no doubt.
4:15.20.-A sudden dazzling flash and totality ends. The
lower limb of the sun is uncovered, and the “shadow bands”
reappear. We all try to gauge their size, distance apart, di-
rection, etc., but it is a hard thing to do; much variety of
opinion; the majority seem to favor a direction E of north,
and to think that they are about six inches apart. (I should
have thought nine or ten.) They are gray wraiths of shadow
—something like smoke, or the shadows that ripples make
in a pool. They move faster than I expected. I hear the
cameras click, but I think the light is too faint and the bands
too fast for any successful result. All the stars disappear at
once but Venus, Jupiter, Mars, Mercury, and Saturn are still
visible. The corona is gone like a flash. The rest is an
anti-climax.
4:20.-Everybody seems satisfied that good results have
been obtained. Father Pigot still keeps his pyranometer
going—also Professor Vonwiller and Mr. Briggs and Mr.
Aston in their shed for a while with their “intensity” records.
4:50.—Everybody adjourns to the other observing stations
to exchange views.
5:14.55.-Last contact. Poor old sun l Nobody pays any
attention to him now. Sic transit gloria solis.
5:20.-Everybody photographed, everybody happy, every-
body tired. Finis. (I am told that certain flowers called,
locally, “bluebells,” closed during totality. The cocks crew
quite a bit when the light returned, and the fowls, looking
very foolish, came off their perches. Also many birds left
their roosts in the trees.) -
XIX
EIOW THE ASTRONOMER OBSERVES AN ECLIPSE
LONG before the track of a total solar eclipse is due to pass
over the earth’s surface the astronomer is considering the ad-
visability of placing himself and his instruments within it for
the purpose of making certain important observations that can
be made only when the sun is totally obscured.
If the eclipse path touches land under favorable circum-
stances, that is, with the sun at a considerable elevation above
the horizon, with promising weather conditions, and a dura-
tion of totality of approximately two minutes or over, the
chances are that every effort will be made to have at least
one eclipse expedition in the field. Frequently astronomers
from a number of the leading countries of the world occupy
stations at different points within the shadow track. When
the total phase is exceptionally long, say from four to six
minutes, special efforts are made to observe it even if it is
necessary to travel half way round the world to do so.
Expeditions have been sent to strange and out of the way
corners of the globe to observe total eclipses of the sun. A
coral island in mid-Pacific, the banks of the Saskatchewan,
the island of Sumatra, the coasts of Siberia, Labrador and
Africa have been some of the objectives of eclipse expeditions.
Some of these expeditions have attained splendid success,
others have met with defeat from clouds but the sum total of
knowledge gained from the observation of eclipses has been
well worth the trouble and expense incurred in observing
them.
92
HOW THE ASTRONOMER OBSERVES 93
The weather has ever been the despotic ruler over the fates
of eclipse expeditions. It is customary to get records whenever
possible of weather conditions for a period of several years
at points favorably located within the shadow path in order
to minimize the chances of selecting stations where the weather
promises to be unfavorable at the particular time of the year
and day when the eclipse will occur.
For the first time in the history of eclipse expeditions,
insurance was taken out against failure to obtain observations
during the period of totality in the case of the eclipse of
September 10, 1923. This was done by the Sproul Observa-
tory Expedition of Swarthmore College, which was stationed
at Yerbanis, Mexico. As it happened, this was the only Ameri-
can expedition sent out to observe this eclipse that did not
meet with defeat from clouds. Let us hope that more ex-
peditions will be insured in the future if this is to be the re-
sult The prediction of weather conditions, after all, is large-
ly a lottery as can be judged from the fact that the best
weather conditions for the time of the year at which this
eclipse occurred promised to be in California, and on the
western coast of the peninsula of Lower California. Here
most of the expeditions located and here, as it happened, dense
clouds and fog prevailed during the eclipse hour.
The Mexican National Observatory expeditions, located at
Yerbanis and Laguana Seca, Mexico, obtained valuable records
of this eclipse at both stations though torrential rains fell on
the morning of the eclipse at Yerbanis and at the beginning
of totality the sun was visible through thin clouds. These
did not affect the photographs, however, and rapidly cleared
away, leaving the latter half of the eclipse visible in a perfect-
ly clear sky so that the entire program was carried out suc-
cessfully by both the Swarthmore and Mexican expeditions.
94 A HANDBOOK OF SOLAR ECLIPSES
The chief object of all eclipse expeditions is to obtain photo-
graphs of the corona, for the purpose of studying its form,
structure, and extent, as well as spectrograms, that is, photo-
graphed spectra, of the corona and of the lower solar atmos-
phere—the reversing layer and the chromosphere—for the pur-
pose of finding out the nature of the unknown elements that
exist in the corona and the constitution of both corona and
the solar atmosphere.
The equipment of the average eclipse expedition consists
essentially of telescopic cameras, of focal length between two
and nine feet generally, for photographing the outer extensions
of the corona and the region surrounding the sun, also, in
addition to these telescopic cameras, several grating or prism
spectrographs for obtaining photographs of the flash spectrum
and the spectrum of the corona. The equipment may include,
in addition, interferometers for determining the rotation of the
corona and instruments for measuring the nature and inten-
sity of its light. In recent years a moving picture camera is
frequently included in the equipment of eclipse expeditions
for the purpose of obtaining photographs of educational value
of the eclipse camps and instruments and of all phases of the
eclipse from first to last contact.
A large photographic telescope, or camera, of focal length
forty to sixty feet, which takes photographs of the eclipse
on a large scale is the most unwieldy and cumbersome piece of
the eclipse outfit. It is mounted either in the form of a tower
pointed directly at the sun or horizontally. In the latter
case it is fed by means of a coelostat which reflects the light
from the sun and which may at the same time reflect light to
other instruments. This large camera usually has a lens of
five or six inches aperture and forms an image of the sun five
to seven inches in diameter. The sixty-five foot camera used
HOW THE ASTRONOMER OBSERVES 95
by the U. S. Naval Observatory expedition to Baker, Oregon,
in 1918 gives an image over seven inches in diameter and the
six-inch photographic telescope of the Yerkes Observatory
used in 1900 and 1918 has a focal length of sixty-one
and a half feet and gives a solar image seven inches in
diameter. It was planned to use this instrument at
the eclipse of September 10, 1923, in a horizontal position,
feeding it from a coelostat with an eleven and a half inch
flat mirror.
During the total phase of the eclipse, eight or ten photo-
graphs can usually be taken with such an instrument, the ex-
posures generally ranging in length from about one second
to over sixty seconds. At Fort De Kock, Sumatra, in 1901,
Prof. G. H. Peters of the U. S. Naval Observatory Expedition
took ten photographs with the forty-foot camera, with ex-
posures ranging from one-half to sixty seconds. The Yerkes
Observatory Expedition stationed at Catalina Island in 1923
planned to take six exposures with their sixty-one-foot camera,
two exposures of one second each and four of four, eight, six-
teen and one hundred and twenty seconds respectively. The
Lick-Crocker Expedition to Wallal, Australia, in 1922 took a
long series of photographs with their forty-foot camera, with
exposures ranging from one-fourth of a second to sixty-four
seconds.
The smaller telescopic cameras which are used to photo-
graph the outer corona and field surrounding the sun are
usually mounted on a single polar axis driven by clock work
or by means of a clepsydra or some other device for counter-
acting the diurnal motion of the earth. The motion imparted
to the axis by this means is opposite in direction and equal
in amount to that of the earth on its axis so that the solar
96 A HANDBOOK OF SOLAR ECLIPSES
image appears immovable in the field. Often the spectro-
graphs and other instruments are also mounted upon the same
polar axis. The Lick-Crocker Expedition to Wallal in 1922
attached to one polar axis a camera of five inches aperture
and sixty-six inches focal length and five spectrographs. The
Sproul Observatory expedition to Yerbanis, Mexico, mounted
on one polar axis, two grating spectrographs, an Etalon inter-
ferometer for determining the rotation of the corona, and a
motion picture camera. On another polar axis were mounted
the “twin Einstein” cameras fifteen feet focal lengths and
6% inch apertures with quadruple lenses which covered an
18x18 inch plate.
The expedition to Wallal had a pair of similar Einstein
cameras and in addition another Einstein pair of four-inch
aperture and five-foot focal length. These cameras are em-
ployed primarily for photographing field of stars immediately
surrounding the eclipsed sun for the purpose of studying the
Einstein effect, which is the displacement of the images of
stars near the sun from their normal position and away from
the sun as a result of the effect of the sun’s gravitational field
upon the path of a ray of light passing through it.
It was predicted by Einstein some years ago that this effect
would be observable at the time of a total solar eclipse, when
the stars near the sun are visible. At the eclipse of May 12,
1919, the British expeditions to Brazil and Africa first ob-
tained evidence that such an effect might exist and re-
Sults of their observations have been confirmed by observations
made with the Einstein cameras at Wallal in 1922 by the
Lick-Crocker Expedition. So perfect is the agreement be-,
tween the observed deflections recorded by these four cameras
and the predicted “Einstein effect” based upon the principles
Above: The camp of Sproul Observatory Expedition at Yerbanis, Mex-,
ico. Total Solar Eclipse September 10, 1923. Showing the sixty foot
camera, in front of which are the Einstein cameras and a polar axis
conveying a number of smaller instruments.
Below: Camp of Lick-Crocker Eclipse Expedition, Wallal, Australia. Total
Solar Eclipse September 21, 1922. Showing the Polar Axis, carrying
Spectrographs, five-inch Telescope, and two Short-Focus Cameras. The
south side of the shelter for the Einstein Cameras is visible at the right.




HOW THE ASTRONOMER OBSERVES 97
of the Einstein Theory of Relativity that Prof. W. W. Camp-
bell, director of the Lick-Crocker Expedition, considers that
so far as the Lick Observatory expeditions are concerned, the
problem has been settled in favor of the Einstein effect and
will not be taken up by future expeditions sent out by that
observatory. The results obtained by the Sproul Observatory
Expedition which undertook a solution of the same problem
during the eclipse of Sept. 10, 1923, have not been reduced yet
and are awaited with great interest as this is considered to be
one of the most important physical problems of the present
age.
Two, three or even five minutes seem a ridiculously short
period to be allotted at intervals of a year or more for the
carrying on of a series of scientific observations. But with
a battery of cameras and spectrographs and the additional
instruments with which the average eclipse expedition is
equipped a very complete record of an eclipse can be made
even within as brief a period as a single minute. With clear
skies a single expedition will obtain at least a score of valuable
photographs of the corona within two minutes or less, and in
addition spectroscopic and other records of the eclipse of
great value. If several expeditions at widely separated sta-
tions are in the same eclipse path results of correspondingly
greater value are to be expected. The records of an eclipse
are of value not only in themselves but because they fit into
the chain of eclipse records taken at different times in the
sunspot cycle and furnish a needed link in the chain of con-
tinuous solar changes. For this reason even a single photo-
graph of the corona of an eclipse has a very special value
and is greatly to be desired. Every effort should be made
for this reason to obtain photographs of the corona at as many
98 A HANDBOOK OF SOLAR ECLIPSES
different points as possible in the eclipse path for if clouds
occur at one point fair skies may be experienced at another,
as was well exemplified in the case of the eclipse of 1923. For
this reason plans should be made to obtain observations of the
coming eclipse of January 24, 1925, at as many points as pos-
sible along the shadow path. Success may be attained where
least expected. -
An expedition usually arrives at the site selected at least
six weeks before the day of the eclipse. This is none too soon
for all instruments must be assembled, erected and adjusted.
This includes the building of shelters for the instruments,
dark rooms, etc., and the erecting of a tower or long horizontal
enclosure for the long-focal, telescopic camera, forty, sixty or
sixty-five feet in length.
The program of work for each instrument and observer is
thought out far in advance and as soon as everything is in
readiness rehearsals and drills are held frequently so that dur-
ing the few vital moments of totality no fatal delay or blunder
will occur that might bring to naught weeks of painstaking
prparations.
One might imagine that if anyone were to have the oppor-
tunity to see the eclipse at its best it would be the astronomer,
but in general, he sees less of the eclipse than anyone else.
His undivided attention must be given to the instrument or
work assigned to him and often he has no opportunity to cast
as much as a glance toward the heavens when the corona is
shining forth in all of its glory. A noted astronomer who
had been on a number of eclipse expeditions once remarked
that he had never SEEN a total solar eclipse. -
The weeks of his stay at the eclipse camp preceding the day
of eclipse are busy and nerve-straining ones for the astron-
HOW THE ASTRONOMER OBSERVES 99
omer. The eclipse cannot be postponed or delayed. Every-
thing must be done by a certain minute on a certain day and
there is the ever present anxiety as to what the weather will
be during the fateful moments of totality. Will all of his
labor be in vain or will it be crowned with success? The god
of the weather alone will decide. The astronomer has need to
be a good sport or a philosopher, or both.
XX
THE IMPORTANCE OF ECLIPSES
WHY spend so much time and money and effort in observing
total eclipses of the sun? It might be hard to explain this
to the satisfaction of one who measures the value of everything.
in terms of dollars and cents. Yet even the practical value
that may result from the observation of total solar eclipses is
by no means negligible. Helium, now used for inflating air-
ships and balloons and far more suitable for this purpose than
the inflammable hydrogen gas, was discovered in the flash
spectrum of the sun by eclipse expeditions long before it was
discovered on earth. Lines of unknown origin, attributed to
a hypothetical element, ‘‘coronium,” have also been found in
the corona, and efforts are now being made to “run these
lines to earth.” There is nothing in this universe more im-
portant to us than the sun. We are dependent upon it for
our very existence and the laws that govern its output of life-
giving heat and energy are of vital interest to us. The corona
is intimately associated with and dependent upon the sunspot
cycle of solar activity, the cause of which is still a mystery.
So far no method has been devised for studying the corona
without an eclipse. Find a way to observe the corona in day-
light and a great step will be taken toward the solution of
the mystery of the sunspot cycle and the variability in the out-
put of solar energy, which is so closely connected with meteor-
ological and magnetic changes on the earth. We need ob-
º servations of eclipses to tell us more of the secrets of the sun.
*::: in the sun are the same elements with which the scientist
• ." 100
August 24, 1909.
Solar prominences are now photographed continually in broad daylight by means of the spectroscope. -
above view shows a prominence 80,000 miles high taken without an eclipse at the Mt. Wilson Observatory,
The
-
-
---
-
-
-
º
º

IMPORTANCE OF ECLIPSES 101
works in his physical and chemical laboratory but in a form
and at a temperature that cannot be reproduced here. Eclipse
observations of the corona furnish the means for studying
the behavior of these same elements and possibly other un-
known elements under the unusual conditions that exist at the
surface of the sun and in its immediate vicinity. In this great
research laboratory of the sun, as in our physical and chern-
ical laboratories on earth, great and far-reaching discoveries
may be made.
Of equal importance with the corona as a subject of study
during total eclipses of the sun in recent years has been the
behavior of rays of light passing through the gravitational
field of the sun. Here we may learn something of the nature
of light itself. At time of total solar eclipse stars become
visible even close to the edge of the eclipsed sun. The light
from these stars must pass through the sun’s gravitational
field before it enters our eyes. Some years ago Prof. Albert
Einstein predicted, on the basis of his now celebrated theory
of relativity, that light would be deflected from its course upon
passing through a gravitational field and that for light passing
through, the sun’s field the deflection would be great enough
to be measured. A photograph of the star field surrounding
the eclipsed sun was to be compared with the same field of
stars photographed some months later when the sun was in
another part of the heavens. There should be a displacement
of the star images in the field surrounding the eclipsed sun
away from the Sun and varying in amount with distance of
the star image from the edge of the sun. The exact amount
of the deflection was computed from the theory and found
to be one and seventy-five hundredths of a second of arc for a
star at the edge of the sun. This was the maximum deflection
and it decreased rapidly with distance outward from the sun,
102 A HANDBOOK OF SOLAR ECLIPSES
being too small to measure at a distance of one diameter of
the Sun.
This “Einstein effect,” as it was called, was sought for by
the British eclipse expeditions to Brazil and Africa during the
total solar eclipse of May 29, 1919, a particularly favorable
time as the sun was then in a rich field of stars. Measure-
ments of the photographic plates seemed to show conclusively
that such an effect did exist. The Lick-Crocker Expedition
to Wallal, Australia, also undertook the solution of the same
problem at the time of the total solar eclipse of Sept. 21, 1922.
The results obtained were even more favorable to the Einstein
theory than those obtained by the British expeditions in 1919,
the displacements of a large number of star images, when
measured and reduced, giving almost exactly the value pre-
dicted from the Einstein theory. The solution of the problem
was again undertaken at the eclipse of Sept. 10, 1923, by the
Swarthmore College Expedition to Yerbanis, Mexico. The
plates obtained by this expedition with their Einstein cameras
have not been completely reduced up to the present time.
We are not entering into any discussion of the Einstein
theory of relativity here but it must be admitted that there
is every reason to believe that light is bent from its course
upon passing through the sun’s gravitational field as if it
were a material substance having mass and weight. This dis-
covery, made solely by the observation of total solar eclipses,
is of great importance to the physicist as well as to the astron-
omer, for it may alter some of his most fundamental concep-
tions regarding the nature of light. Whether the bending of
the rays of light on passing near the sun is due to the Ein-
stein effect or some other cause is the subject of spirited con-
troversy among scientists at the present time. It is best to
keep an open mind in this matter so far as possible and await
IMPORTANCE OF ECLIPSES 103
the accumulation of additional evidence before forming con-
clusions.
Of secondary importance to these problems, yet by no
means to be overlooked, are the observations of the times of
the beginning and ending of the total phase of the eclipse,
which give a means of comparing the true and predicted
positions of the moon in the heavens and correcting and im-
proving the tables upon which the computation of eclipses
are based. These observations are also of value in getting at
the cause of the irregularities in the motion of the moon, which
are of much concern to the theoretical astronomer.
Here also we may mention the value of the calculations of
past eclipses in fixing the chronological order of many im-
portant dates in history. It is possible for the astronomer,
working backward with the aid of tables which give the posi-
tions of sun and moon for many centuries, to determine the
dates of past solar and lunar eclipses and the location of the
tracks of solar eclipses on the earth's surface. Comparing the
dates and tracks of these past eclipses with accounts of eclipses
mentioned in history, it is possible to determine the chrono-
logical order of many important events in history running
back as far as several thousand years before Christ. This
has often been of great value in settling doubtful or disputed
dates in history.
A knowledge of the eclipse Saros and the ability to pre-
dict eclipses has at times invested its possessor with almost
supernatural powers. Columbus used this knowledge of
eclipses to excellent advantage on his third voyage to the New
World, possibly saving his own life and that of his compan-
ions thereby. This happened in the early spring of 1504,
when the Indians on the island of Jamaica were threatening
to cut off his food supply. A total eclipse of the moon was
104 A HANDBOOK OF SOLAR ECLIPSES
to occur in the evening on the first of March. Calling the
chiefs of the tribes together on that day Columbus reproached
them with refusing to supply him with provisions and
prophesied that the divine vengeance would fall upon them
that very night when the moon would change her color and
lose her light as a sign of the evils that would be sent upon
them from the skies.
As it happened the night of the first of March was clear
and the full moon shone brilliantly. At the predicted time,
as prophesied by Columbus, the light of the moon began to
fail. Sir A. Help, writing of this event in his “Life of Colum-
bus,” says, “At the appointed time the phenomenon took
place and the wild howls of the savages proclaimed their ab-
ject terror. They came in a body to Columbus and implored
his intercession. They promised to let him want for nothing
if only he would avert this judgment. As an earnest of their
sincerity they collected hastily a quantity of food and offered
at his feet... He consented to intercede for them, and, retiring
to his cabin, performed, as they supposed, some mystic rite
which should deliver them from the threatened punishment.
Soon the terrible shadow passed away from the face of the
moon, and the gratitude of the savages was as deep as their
previous terror.’’
It may be counted not least among the results of sending
eclipse expeditions to many corners of the globe that such
pitiable exhibitions of fear at the occurrence of these natural
phenomena, which were so common in the past even among
the more civilized races, are becoming increasingly rare. In
their place is appearing an intelligent interest and enthusiasm
for increasing the sum of human knowledge through the
scientific observation of these most impressive phenomena.
YXI
SOME NOTED ECLIPSES OF THE PAST
IN the historical records of all nations are found many
references to eclipses. Such was the superstitious dread and
fear with which eclipses were regarded that special note was
usually made of their occurrence, the historian sometimes re-
ferring to them as signs of divine displeasure or portent of
evil.
The earliest eclipse recorded in history is an eclipse of the
sun which occurred on October 22, 2136 B. C., in the reign of
the Chinese Emperor Chung K’ang. The record tells also of
the sad fate of the two court astronomers — Hsi and Ho, -
who incurred royal displeasure and were beheaded not only
because they failed to predict the eclipse but also because
they were so drunk at the time of its occurrence that they
could not perform the customary astronomical rites | These
consisted at that time, as they do even at the present time in
some parts of Asia, of beating drums, sounding gongs and
shooting arrows for the purpose of scaring off the black
dragon which was on the point of devouring the sun.
The next reference to an eclipse also appears in the Chinese
records and was made by Confucius, who stated that an
eclipse occurred during the reign of the Emperor Yew Wang,
who was known to have reigned from 781 B. C. to 771 B. C.
The eclipse referred to has been identified as the eclipse of
June 4, 780 B. C. º -
Records of thirty-six eclipses that occurred between the
years 720 B. C. and 495 B. C. appear in the Chun Tsew,
105
106 A HANDBOOK OF SOLAR ECLIPSES
written by Confucius, which is one of the Five Classical Books
of China with which every well-educated Chinaman is expected
to be familiar. Many other eclipses are recorded in a Chinese
historical work of 101 volumes which gives an outline of
Chinese history from the earliest times to the end of the Yuen
Dynasty, 1368 A. D. Not only eclipses of the sun but also
comets are mentioned in this work, but, strange to say, no
eclipses of the moon. .
There is at least one reference to an eclipse in the Bible.
In Amos, VIII, 9, we read:—“And it shall come to pass in
that day, saith the Lord God, that I will cause the sun to go
down at noon, and I will darken the earth in the clear day.”
This is plainly a reference to a solar eclipse and the eclipse
of June 15, 763 B. C. has been identified as the one meant.
This was the eclipse of Ninevah of which there is a contem-
porary record on an Assyrian tablet. Calculations showed
that this eclipse was also total at Samaria, where it was pre-
dicted. A passage in Isaiah, XXXVIII, 5-8, is also believed
to be a reference to the eclipse of January 11, 689 B. C., visible
in Jerusalem.
Six eclipses, namely, three of the sun, including the eclipse
of Ninevah in 763 B. C., which were recorded on Assyrian
tablets, and three of the moon, observed in Babylon, have
fixed the dates of Assyrian chronology with great exactness.
The earliest date in Assyrian chronology accurately deter-
mined by means of these records of eclipses is the year 911
B. C. Earlier than that date there is much uncertainty as
to the exact dates of historical events.
The most famous of classical eclipses and the first to be
definitely predicted was that of Thales of 585 B. C., to which
We have referred in an earlier chapter, which put an end to
the battle between the Lydians and the Medes, and brought
ECLIPSES OF THE PAST 107
about the conclusion of a lasting treaty. Numerous references
to eclipses appear in the writings of Greek historians but it
would be impossible to consider any of these in detail here.
Many interesting accounts of eclipses that occurred in the
Middle Ages appear in the Anglo-Saxon Chronicle. The
first eclipse noted in English chronology was the eclipse of
538 A. D. which occurred in the reign of Henry, King of the
West Saxons. The sun's disk was three-fourths covered in
London at maximum obscuration.
On October 29, 878 A.D. there was a total eclipse visible in
London. No other solar eclipse total in London occurred
until the year 1715, more than eight centuries later, though the
eclipse of December 22, 968, was very nearly total in London,
and also the eclipse of March 20, 1140.
The eclipse of August 30, 1030, is known as ‘‘the eclipse
of Stiklastad” for the reason that the sun was totally eclipsed
on that date in Norway at a place known as Stiklastad while
a battle was in progress in which Olaf, the King of Norway,
was said to have been killed.
The eclipse of August 2, 1133, total in Scotland, was one of
the most noted eclipses of the middle ages. It was taken
at that time as a portent of misfortune to Henry the First,
who went over sea that year never to return and was on his
voyage at the time of the eclipse. His death in Normandy
two years later seems to have made a great impression on the
popular mind and to have been directly associated with the
occurrence of the eclipse. It was alluded to in this connec-
tion both in the Anglo-Saxon Chronicle and by William of
Malmesbury. The path of this eclipse also crossed Europe,
entered Palestine, and passed over Jerusalem.
In 1140 occurred the eclipse that was long supposed to have
been total in London but which calculation has shown was
108 A HANDBOOK OF SOLAR ECLIPSES
total at Shrewsbury, Derby, Nottingham and Lincoln but not
in London. The duration of this eclipse in England was
nearly three and a half minutes. One of the most celebrated
eclipses of the middle ages was the eclipse of June 17, 1433,
which was total in Scotland, the hour of the eclipse being long
remembered there as the ‘‘Black Hour”, as totality was ex-
ceptionally dark. The duration of totality at Inverness was
over four and a half minutes, and at Edinburgh about three
minutes and forty seconds. The path of this eclipse also
passed over Bavaria and Asia Minor to Arabia and was
observed in Turkey near sunset. Scotland was again favored
with a total eclipse on ‘‘Black Saturday,” February 25, 1598,
and on “Mirk Monday,” April 8, 1652. In all three of these
eclipses Edinburgh lay directly in the path of totality. Again
in 1699 the sun was eleven-twelfths obscured at Edinburgh
So this town appears to have been particularly favored by
eclipses during the middle ages. In London, on the other
hand, no total solar eclipse was visible for over eight centuries.
On May 3, 1715, however, London came at last within the
path of a total solar eclipse. This eclipse track crossed
England from Cornwall to Norfolk and was observed by one
of the most noted astronomers of the time, Sir Edmund
Halley. No other total eclipse has passed over London since
that day and there is none in prospect for more than a hun-
dred years to come, though in 1724 another path of totality
crossed the Southern part of England at no great distance
from London. The next total eclipse visible in England is
that of June 29, 1927, of which we will have more to say in
the next chapter.
Mention has been made of eclipses observed in the British
colonies and, later, in the eastern part of the United States
in the latter part of the eighteenth century and during the
ECLIPSES OF TEIE PAST 109
nineteenth century. We are now coming to a period of scien-
tific enthusiasm for the observation of eclipses, and the in-
auguration of the long series of eclipse expeditions that have
obtained such brilliant results both in this country and
abroad. -
In the early ages men were, in general, too inspired with
feelings of awe and fear during the period of totality to make
any observations of value. The corona was referred to
occasionally as a luminous ring of light but its true nature
as a Solar appendage of unusual significance was not recog-
nized until near the middle of the last century. Some be-
lieved even then that both corona and “red flames,” as the
prominences were called, were appendages of the moon instead
of the sun. -
Even scientific observers of eclipses hardly knew what to
look for at time of eclipse until the nineteenth century was
well advanced. The present scientific enthusiasm for observ-
ing eclipses, which has resulted in the dispatch of expeditions
to the shadow path of practically every eclipse available with-
in the past sixty years or more, dates back to the discovery
of Baily’s Beads at the annular eclipse of May 15, 1836.
Though but a minor and unimportant phenomenon it was the
first really scientific contribution to the brilliant series of
eclipse observations and discoveries of modern times. This
discovery, made by Sir Francis Baily, who was not an astron-
Omer by profession, shows what may be accomplished even by
the amateur observer in the field of astronomy as well as
other sciences.
The eclipse of July 8, 1842, crossed Europe from France to
Russia and some of the most noted astronomers of the day
were stationed at different points along the central line to
observe it. Fortunately the eclipse was witnessed under
110 A HANDBOOK OF SOLAR ECLIPSES
favorable circumstances at alſ points. Attempts were then
made for the first time to photograph the corona on iodized
paper but without any results.
The various features of this eclipse were particularly
beautiful and made a deep impression upon the masses of
people who observed it, as well as upon the astronomers. Baily
again observed the “Beads” at Pavia, as well as the mag-
nificence of the corona and the prominences. He refers to the
latter as “three large protuberances apparently emanating
from the circumference of the moon but evidently forming a
portion of the corona.” In speaking of the corona he says,
“The breadth of the corona, measured from the circumference
of the moon, appeared to me to be nearly equal to half the
moon’s diameter. It had the appearance of brilliant rays.
Its color was quite white, not pearl color, nor yellow, nor
red.” Of its first appearance at the beginning of totality he
says, “I was astounded by a tremendous burst of applause
from the streets below, and at the same moment was electrified
at the sight of one of the most brilliant and splendid pheno-
mena that can be imagined. For at that instant the dark
body of the moon was suddenly surrounded with a corona
or kind of bright glory.”
The enthusiasm aroused by the observations of this eclipse
had much to do with the fitting out of expeditions to observe
the eclipse of July 28, 1851, visible in Norway and Sweden
and northern Europe. Many prominent astronomers were
again on hand, including G. P. Bond of Harvard, probably
the first American to visit Europe for the express purpose of
observing a total solar eclipse. Again the skies were clear.
The first photograph of an eclipse was made on this occasion,
a daguerreotype by Busch at Königsberg. At this eclipse also
the Astronomer-Royal of England, Sir George Airy, and other
ECLIPSES OF THE PAST 111
observers saw the enormous lunar shadow speeding away
through the air for a period of fully six seconds after totality
WaS OWer.
It is impossible to even touch upon the long series of eclipse
observations that have been made from that time up to the
present day. The systematic application of photography to
the study of the corona was inaugurated at the time of the
eclipse of July 18, 1860, the first one observable in the United
States after the scientific observation of eclipses had begun.
The first fruits of the application of photography to the
study of eclipse phenomena resulted in the discovery at this
eclipse that the “protuberances” or prominences belonged
to the sun and not to the moon. This became plainly evident
from a study of the photographs.
It was about this time that the spectroscope was coming into
use as an instrument of research in the study of the constitu-
tion of the stars and sun and it was first employed in un-
ravelling the mystery of the composition of the corona and
prominences at the eclipse of August 18, 1868, which was
visible only in India, Siam and the Malay Peninsula. Un-
daunted by the discouraging fact that this eclipse was to
occur so far from home, British, French, German and Spanish
expeditions set out for this far-away track and the brilliant
success attained was well worth the effort. The prominence
lines were of remarkable brilliancy. Hydrogen was easily
identified and the bright yellow line of the, then unknown,
element helium was strongly in evidence. The success of
Janssen in observing the prominences with the spectroscope
after the eclipse was over has been mentioned elsewhere.
From now on the astronomer used effectively these two
powerful aids, the camera and the spectroscope, on all eclipse
expeditions. Little could be accomplished without them. It
112 A HANDBOOK OF SOLAR ECLIPSES
is now but a matter of time before the mysteries of the corona
will be solved by means of them. The chief obstacle in the
way of rapid advance in the solution of the cause of the in-
tricate form and structure of the corona and its association
with the sunspot cycle lies in the extreme briefness of the time
allowed for making observations at each eclipse, on the
average scarcely three minutes.
Yet in the past half century, in which a total period of
considerably less than one hour has been available for the
study of the corona and the field immediately surrounding
the sun, many valuable photographic and spectroscopic
records of eclipses have been accumulated. From the middle
of the nineteenth century up to the present time the work
of obtaining scientific records of eclipses has been carried on at
every total solar eclipse that has been visible in whatever
part of the world it may have occurred, outside of polar
regions.
It has become, indeed, almost a matter of tradition among
astronomers of today to “carry on” in the matter of sending
out expeditions for the observation of total eclipses of the
sun and future generations of astronomers will find little to
criticize in the splendid series of eclipse observations con-
tributed by the astronomers of the present generation. The
Scientific enthusiasm of the astronomers of the present age is
reflected in the quality, as well as the quantity, of valuable
records of solar eclipses that are being collected by eclipse ex-
peditions.
XXII
SOME TOTAL SOLAR ECLIPSES OF THE NEAR
FUTURE
AFTER the total solar eclipse of Jan. 24, 1925, has passed
into history the American astronomer will have to do most
of his eclipse observing abroad. There will be a fine total-
annular eclipse visible in the northwestern states on April
28, 1930, but aside from that no total solar eclipse track will
pass over any considerable portion of the United States until
Feb. 26, 1979, when the path of totality will pass over the
northwestern States again to Canada and Hudson Bay. The
eclipse of March 7, 1970, will be visible in the United States
but only in the state of Florida. There are, however, some fine
eclipses due to arrive in the immediate future in other lands
and these should be well observed.
On June 14, 1926, there will be a total solar eclipse of over
four minutes' duration that will pass from East Africa over
the Indian Ocean to Sumatra, Borneo and the Philippines.
It is probable that every effort will be made to observe this
eclipse as it will occur under very favorable circumstances.
The most suitable stations will probably be found in Sumatra.
It was on this island that the U.S. Naval Observatory expedi-
tion occupied three stations, Solok, Sawah Loento and Fort
De Kock at the time of the total solar eclipse of May 17, 1901,
and obtained some excellent photographs of the corona and
“flash spectrum.”
- 113
114 A HANDBOOK OF SOLAR ECLIPSES
The 1926 eclipse will occur in Sumatra about two o'clock
in the afternoon and in the Philippines shortly before sunset.
The maximum duration of 4 min. 10 sec. will occur in mid-
Ocean South of India. On the east coast of Africa, where the
eclipse will take place in the early morning, the duration will
be a little over two minutes but in Sumatra it will last over
three minutes, which is about the average duration of a total
solar eclipse.
The eclipse of July 9-10, 1926, is an example of an eclipse
track that is completely wasted from the astronomer's point
of view. It is, to be sure, an annular eclipse and so its
scientific value is small compared with that of a total eclipse
but its track from beginning to end lies wholly over the
Pacific Ocean, touching only a few small unnamed islands to
the northwest of the Hawaiian group.
The most interesting eclipse of the near future, after the
eclipse of 1925, will be the total solar eclipse of June 29, 1927.
The path of this eclipse touches the earth at sunrise at a point
in the Atlantic Ocean to the southwest of the British Isles, in
approximate position 41° N. Lat. 16° W. Long. Just missing
the southern coast of Ireland it crosses St. George's Channel
to Liverpool and then passes diagonally over northern Eng-
land to the coast at Seaham Harbor in Durham. From here
it passes over the North Sea to Norway, touching the coast
in approximately 58° N. Lat. and 10° East Long. Passing
about midway between Trondhjem and Christiania in Norway
it crosses the northern part of Sweden to the Arctic Ocean.
Leaving the Norwegian coast in about 70% º N. Lat. and
29% º East Long. it then runs over the Arctic Ocean north
of Nova Zembla to Thaddeus Bay, Siberia, and from here
across the northeastern part of Siberia, north of Kamchatka
ECLIPSES OF THE FUTURE 115
to the Bering Sea, where it leaves the earth at sunset at a
point just north of the Aleutian Islands.
This eclipse will be one of the briefest total solar eclipses
on record. The longest duration, which will occur at a point
on the central line north of Nova Zembla near noon, will be
only fifty seconds. The duration in England will be, at the
most, about twenty-five seconds. On the Scandinavian penin-
sula the duration on the central line will range from thirty
seconds to forty-five seconds.
The total phase of the eclipse will occur at Liverpool at 5:23
A. M. and its duration at this place will be only seventeen
seconds. At Durham the total eclipse will take place at 5:25
A. M. and its duration will be only nine and six-tenths seconds.
In this eclipse the apex of the moon's shadow cone will barely
graze the earth’s surface and the path will be extremely
Ila. TI’OW. - -
Though the total phase of the eclipse occurs in England
about half past five in the morning the sun rises at about half
past three in northern England at this time of the year so the
entire eclipse will take place with the sun above the horizon.
The partial phase will be large all over England, Scotland and
Ireland, as well as in the northern and northwestern part of
Europe, the northeastern part of Siberia and Alaska. The
magnitude of the eclipse will be 96% in London, 98% in
Edinburgh and Dublin and 97% in Glasgow, Oxford and
Cambridge. At Nome, Alaska, and magnitude of the partial
eclipse will be 86%.
It might be imagined that no scientific results of great value
could be obtained at total eclipse when the duration is so ex-
tremely short, but this is not necessarily true. The spectro-
scopic observations of the “flash”, and chromosphere, the
116 A EIANDBOOK OF SOLAR ECLIPSPS
lower solar atmosphere, should be of particular value as they
will be seen to better advantage than at the time of a large
total eclipse when the lower atmosphere, as well as the disk, of
the sun is covered by the moon. At this eclipse the chromo-
sphere should be seen during totality as a rosy circle of light
surrounding the sun. The scenic features of the eclipse should
be particularly beautiful for this reason and also because the
sunspot maximum period will be approaching when the solar
activity is above normal and manifests itself in numerous
prominences and a brilliant corona.
Though it will not be possible to take photographic ex-
posures of any great length a large number of short exposures
could be taken at different points if weather conditions were
favorable, especially if expeditions were scattered along the
path in England, Norway, Sweden and northeastern Siberia.
At this time of year the chances are that clear skies would
favor the observers at many points. The possibilities of ob-
taining valuable results at this eclipse are by no means to be
overlooked. The eclipse will be anticipated with unusual in-
terest in England, moreover, as it will be the first total solar
eclipse visible in England in over two hundred years and the
last that will be total in this country until Aug. 11, 1999, when
the path of totality may graze the south of Ireland and Land’s
End.
Another interesting total solar eclipse of the near future
will be the splendid eclipse of May 9, 1929, of over five
minutes’ duration, occurring shortly after noon in Sumatra
and visible also in the Malay Peninsula and the Philippines.
The eclipse of October 21, 1930, with a duration of less than
two minutes will pass over Melanesia, Polynesia and the south-
ern Pacific to Patagonia, where it will end at sunset. The
eclipse of April 28, 1930, which is a total-annular eclipse, that
ECLIPSES OF THE FUTURE 117
is, annular in one part of its course and total in another part,
will pass from the Pacific Ocean over the northwestern and
north central part of the United States to Canada, Hudson
Bay and Labrador. The eclipse will occur at noon in the
United States, in Oregon or Idaho, and it will probably be
total in this part of its path for a brief period. After the
eclipse of Jan., 1925, this will be the most interesting eclipse
of the twentieth century visible in the United States. The
eclipse of August 31, 1932, duration one and a half minutes,
will come down from Baffin Land across Hudson Bay to
Labrador and will end at sunset in mid-Atlantic. This
eclipse will be visible as a large partial eclipse in the north-
eastern part of the United States.
Three eclipses of the present century will first touch land
in the United States at sunrise but will almost immediately
pass out of the country. The eclipse of July 9, 1945, will
begin in the extreme northern part of the United States, either
in Idaho or Montana, and then will pass across the central
part of Canada to Hudson Bay and over Norway and Sweden
and Russia to Turkestan. This will be a fine eclipse in Can-
ada and Europe but of little value in the United States as
the sun will be in, or very close to, the horizon. The same
may be said of the eclipse of June 30, 1954, which closely
parallels the course of the 1945 eclipse, beginning at sunrise
in North Dakota and passing over Canada, Scandinavia,
Russia and Asia to India. On October 2, 1959, the sun will
rise eclipsed on the New England coast but the path will then
pass over the Atlantic to Africa and across this continent to
the Indian Ocean.
The eclipse of 1927 is the last one for which computations
have been completed in the Nautical Almanac Office up to the
present time (1923). The circumstances of the later eclipses
118 A HANDBOOK OF SOLAR ECLIPSEs
have been taken from Oppolzer's Canon der Finsternisse.
The eclipse tracks shown on the charts in which book were
plotted from only three calculated points and they are in some
cases off from the true positions as much as a hundred miles.
They show closely enough for ordinary purposes, however,
the approximate positions of all total and annular eclipses
for more than two centuries to come. , '
UNIVERSITY OF MICHIGAN
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