PARTIAL ECLIPSE SEEN FROM LONDON
2
6H.
20M.
1
MAG.
96.
6H. ISM.
MAG.
90.
3
6H. 25M. Mag. 90.
These diagrams show the partial eclipse near the greatest phase as
visible from London. T h e sun's altitude (Greenwich) at 6hrs. 20mins.
is 11.7 degrees.
PRINTED
IN
GREAT
BRITAIN
BY
GUILDFORD
BILLING
AND
AND
ESHER
SONS,
LIMITED
PREFACE
T H I S handbook is designed for the countless thousands of
plain people whose interest will be excited by the Total
Solar Eclipse visible in North Wales and England on the
morning of the 29th June next.
Many of them will have little astronomical knowledge.
So I have written with the greatest simplicity and in a
vocabulary of everyday use, avoiding altogether the
temptation of technical terms. No mention occurs in these
pages of ecliptic or nadir, of node, parallax, solstice, precession, or anything of the kind. Nor have I a single angle that
is subtended.
Like myself, the average person is quite incapable of
appreciating the passing of a fraction of a second, and such
fractions have been ruled out.
A useful guide is all that this little work purports to be.
The theory of eclipses and the motions of the heavenly
bodies will be found set out with greater refinement in a
hundred astronomical books.
Two centuries have gone by since last a total solar eclipse
was witnessed in the British Isles.
TOTAL ECLIPSE OF THE SUN ON
JUNE 29, 1927
SUMMER TIME G I V E N IN A L L GASES
h. :nin.
Sunrise at Greenwich
Sunrise at Southport
Sunrise at Hartlepool
..
..
..
..
..
..
4.47
4.47
4.32
AREA OF TOTAL ECLIPSE.
Criccieth
Southport .
Hartlepool .
Eclipse
Begins.
h. min.
5.29
5.30
5.31
Total
Eclipse.
h. min.
6.23
6.24
6.25
Eclipse
Ends.
h. min.
7.20
7.21
7.23
PARTIAL ECLIPSE.
Eclipse
Begins.
h. min.
London
Cambridge .
Manchester.
Newcastle .
Oxford
Edinburgh .
Armagh
Dublin
5.26
5.27
5.30
5.32
5.27
5.33
5.33
5.31
Greatest
Phase.
h. min.
6.20
6.21
6.23
6.26
6.21
6.28
6.26
6.25
Eclipse
Ends.
h. min.
7.17
7.19
7.21
7.23
7.18
7.25
7.23
7.21
For the magnitude of partial eclipse at a number of
towns in the British Isles see page 41.
PATH OF THE TOTAL ECLIPSE AND
TIMES ON OR NEAR THE
CENTRAL LINE
Time of
Central
Eclipse.
h. min.
Duration
of Total
Eclipse.
seconds.
degrees.
Criccieth
6.23
22
10
Rhyl
6.23
22
11
Southport
6.24
23
11
Lytham
6.24
22
11
Preston
6.24
22
12
Clitheroe
6.24
21
12
Barnoldswick
6.24
18
12
Settle
6.24
23
12
Leyburn
6.25
24
12
..
Sun's
Altitude.
Richmond
..
6.25
24
13
Darlington
..
6.25
24
13
Yarm
6.25
23
13
Stockton-on-Tees
6.25
24
13
Middlesbrough
6.25
24
13
Hartlepool
6.25
24
13
..
4
S O L A R E C L I P S E OF 1927
W H A T HAPPENS AT SOLAR ECLIPSE
[Summer Time is given]
LOOK for the first contact of the eclipsing Moon with the
solar disc on the Sun's right-hand side. This takes place
at 5.29 a.m., when the onlooker is stationed towards the
western end (Carnarvonshire) of the shadow path marked on
the map. Contact takes place two minutes later at the
eastern (Durham) end of the path.
Seconds are omitted, as a full minute may well pass
before the unaided eye notices that a notch, gradually
enlarging, is being eaten out of the solar disc.
The phases of partial eclipse will soon become more
strikingly evident. In half an hour the advancing Moon
will have cut out the centre of the Sun, whose face thereafter
begins to take the form of a true crescent. The crescent
itself rapidly narrows, and 54 minutes after first contact the
Sun is wholly obscured to those within the shadow area.
At 6.23 a.m. (Carnarvonshire) and 6.25 a.m. (Durham
total eclipse is in progress.
The shadow path across North Wales and England is
about 30 miles in breadth, slightly widening as the trail of
the shadow spot runs easterly. The duration of totality increases as the station lies more eastward, and a second or
two in length of view of the corona may be gained by choice
of station in this direction.
It is of more importance to be near the central line if
possible. Those so situated will enjoy the longest view.
Even to observers thus favoured, total eclipse lasts only from
5
T H E " DAILY TELEGRAPH "
6
22 to 24 seconds, according to the position of the observer
on the western (shortest totality) or eastern ends of the path.
As the central line is left, with each mile the duration of
totality becomes reduced, at first slowly. Thus two or three
miles away the loss is not appreciable, a mere part of a
second. But 10 miles from the central line, as at Bootle and
Chorley, the totality will be reduced to about 18 seconds,
and it continues to lessen as the limiting lines are nearer
and nearer approached. Within the last 3 miles the
decrease is rapid.
To those actually upon the limiting lines, as at Sunderland,
Lancaster, and Burnley, the eclipse may be termed " total
but not continuous "—that is to say, totality will be reached
only to be at the same moment passed.
Warning is necessary of the risk of gazing at the Sun with
unprotected eyes during the earlier phases of the eclipse.
Actual danger to the sight is reduced upon this occasion
because the Sun is low towards the horizon. But that peril
escaped, the retina may yet be left irresponsive in the
moments when the best vision is required. A simple
experiment may be made on any bright, clear day, by
glancing up momentarily at the Sun and then looking down.
The eye seems filled with moving colour patches, and many
seconds pass before anything distinct can be made out.
At an eclipse wherein totality is so short, no time can be
sacrificed without irrecoverable loss.
Accordingly, the onlooker should provide himself with
smoked glasses of at least two densities—that of lesser
density for using when little of the Sun can be seen. More
handy and equally serviceable are old developed photographic
negatives, or tinted spectacles or pieces of coloured glass.
Until the bright solar crescent has become very small, and
the loss of light on the Earth as total eclipse draws near is
7
G U I D E T O T H E ECLIPSE
noticeable, the unprotected eye should not be staring at
the Sun.
The late Dr. Peters, when asked what single instrument
he would select for observing an eclipse, replied, " A pillow."
The spectacle of total eclipse is a naked-eye one, and is best
seen without the use of shaded glasses or instruments of
any kind. All the better will the eyes be able to grasp its
beauty and grandeur if they are bandaged for a few minutes
as totality approaches.
ROTATION OF THE S U N , JUNE 29.
Showing position of the axis and solar equator.
What happens at total eclipse is that a screen—the Moon—
is held up outside the Earth's atmosphere to cut off the direct
sunrays.
It would be useless to hold up such a screen within our
atmosphere, because particles in our atmosphere so scatter
the sunrays by reflection that the light immediately about the
screen is stronger than that given out by the Sun's appendages. Hold up a shilling at arm's length against the Sun ;
though direct sunrays are thereby cut off, all around the
shilling is a glare of intense brightness. Keep away the
sunrays for a considerable distance around the observer, and
the effect is prevented. That is done at eclipse by the
Moon thrusting its dark body between Earth and Sun.
T H E " DAILY TELEGRAPH "
8
Those within the shadow spot stand, as it were, at the bottom
of a great circular shaft made through our atmosphere, into
which no direct sunlight can enter. The sunlight being
thus disposed of, we are able to see the fainter immediate
surroundings of the Sun, which remain invisible in ordinary
daylight. As observers have expressed it, the Sun is
" put out."
In its place is a dark globe mysteriously suspended in the
heavens—the Moon. Around the edge of that dark globe
the Sun's " red flames " appear, and all about it extends the
gorgeous, pearly-white, streaming corona. It is only on
occasions of eclipse that these appendages of the Sun are
visible for the few minutes—in the case of this eclipse it
will be seconds only—that totality lasts, and they fade at
once from sight as the first direct shafts of sunlight reappear
from round the Moon's edge, to announce to all watchers
that total eclipse is over.
The spectacle presented is best described in the words of
those who have actually seen it at past eclipses. Accounts
will vary, but by putting all together the onlooker may
acquaint himself with what he should look for—and what,
if he is lucky, he may expect to see. But a guarded word is
necessary. The personal equation has a very large bearing
upon all that may be seen during the few excited moments of
a solar eclipse. One man or woman will be immensely
impressed by what is unquestionably one of the most striking
manifestations of natural forces; another, of a different
nature, may find little in it. The last is the one to be pitied.
First let us note the appearances on sky and land as the
Moon's shadow with terrific speed sweeps down upon and
races across the Earth. It comes silently : " a vast, palpable
presence seems overwhelming the Earth." The speed of
the shadow across England in June is about 90 miles a
9
G U I D E T O T H E ECLIPSE
minute ; actually it travels faster, for the surface of the Earth
is moving by rotation in the same direction. On account of
the Earth's rotation, the duration of an eclipse is lengthened.
SIZE OF THE MOON.
Face of the Moon is shown against the map of Europe.
Professor J. D. Forbes, of Edinburgh, from the height of
the Superga, near Turin, last century witnessed an eclipse
in a nearly cloudless sky. He says :
I perceived in the south-west a black shadow like that of a
storm about to break, which obscured the Alps. It was the
lunar shadow coming towards us. I confess it was the most
terrifying sight I ever saw. As always happens in the cases of
sudden, silent, unexpected movements, the spectator confounds
real and relative motions. I felt almost giddy for a moment as
though the massive building under me bowed on the side of
the coming eclipse.
Another witness, who had been looking at some bright
cloud just before totality, states: " The bright cloud I saw
T H E " DAILY TELEGRAPH "
10
distinctly put out like a candle. The rapidity of the shadow,
and the intensity, produced a feeling that something material
was sweeping over the Earth at a speed perfectly frightful.
I involuntarily listened for the rushing noise of a mighty
wind."
Such are the emotions which people have experienced
when the shadow has engulfed them. Naturally its approach
and departure are best seen from heights, as from a mountain
top, with great plains stretched out below. The shadow is
not a moment still. It reaches Earth as a spot that would be
circular were the Sun directly overhead, but on the 29th June
in England (with a low Sun) will be a long ellipse, which
traces a path about 30 miles wide as it races away over sea
and land with the speed of the Moon across the sky.
The observer sees, as it were, the actual velocity of one of
the heavenly bodies brought down to him. The shadow
rushing away has been watched for five or six seconds after
totality has ended.
Sir George Airy, one of our famous line of AstronomersRoyal, was a dry, unemotional person in his relations with
his fellow-men, not one who would be expected to be moved
easily. In vivid language, after this same Italian eclipse, he
described the changes wrought in the sky and upon the
countryside during the minute or so before the Sun vanished :
At this time and to the totality the appearances were very
awful. The gloom increased every moment ; the candle seemed
to blaze with unnatural brilliancy; a large cloud over our heads,
whose appearance I had not particularly remarked, but which I
think was of the cumulo-stratus character, became converted
into a black nimbus, blacker, if possible, than pitch, and seemed
to be descending rapidly; its aspect became horribly menacing,
and I could almost imagine that it appeared animated. Of all
the appearances of the eclipse, there is none which has dwelt
more powerfully upon my imagination than the sight of that
terrible cloud.
G U I D E T O T H E ECLIPSE
11
Sun overhead,
round.
Sun low towards horizon. T h e shadow spot
takes the form of a long ellipse.
FORM OF THE SHADOW SPOT.
The shadow was upon the cloud, causing the effects
described by Airy in his last sentences.
Professor Langley, at the first eclipse he witnessed, in
Kentucky (1869), was not less impressed by the aspect of
the Moon itself at the great moment when totality is reached.
He wrote :
The mysterious corona is only seen during the brief moments
while the shadow is flying overhead; but as I am undertaking to
recall faithfully the impressions of the instant, I may admit that
I was at the time equally struck with a circumstance that
may appear trivial in description—the extraordinary globular
appearance of the Moon herself. We all know well enough that
the Moon is a solid sphere, but it commonly looks like a bright
T H E " DAILY TELEGRAPH "
12
flat circle fastened to the concave of the starry vault; and now,
owing to its unwonted illumination, the actual rotundity was
seen for the first time, and the result was to show it as it really
is—a monstrous, solid globe, suspended by some invisible
support above the Earth, with nothing apparent to keep it from
tumbling on us, looking at the moment very near, and more
than anything else like a gigantic cannon-ball, hung by some
miracle in the air above the neighbouring cornfield.
A fine imaginative faculty came into play there. We may
not all be so well endowed. The same picturesque pen has
given an observation of the corona made during a very brief
eclipse, the corona being the great central feature of interest
at every total solar eclipse :
Not till the Sun was very nearly covered did the light of day
about us seem much diminished. But when the Sun's face
was reduced to a very narrow crescent the change was sudden
and startling, for the light which fell on us not only dwindled
rapidly, but became of a kind unknown before, so that a pallid
appearance overspread the face of the Earth with an ugly livid
hue; and as this strange wanness increased a cold seemed to
come with it. The impression was of something unnatural ;
but there was only a moment to note it, for the Sun went out as
suddenly as a blown-out gas jet, and I became as suddenly aware
that all around, where it had been, there had been growing into
vision a kind of ghostly radiance, composed of separate pearly
beams, looking distinct each from each, as though the black
circle where the Sun was bristled with pale streamers, stretching
far away from it in a sort of crown. This was the corona.
But in a few seconds all was over; the sunlight flashed from one
point of the Moon's edge and then another, almost simultaneously, like suddenly kindled electric lights, which as instantly
flowed into one, and it was day again.
General Myers watched a solar eclipse under favourable
circumstances from the summit of the White Top Mountain,
Virginia, 5,500 feet above sea-level, and gives this account:
To the unaided eye the eclipse presented during the total
obscuration a vision magnificent beyond description. As a
centre stood the full and intensely black disc of the Moon,
13
G U I D E T O T H E ECLIPSE
surrounded by the aureola of a soft bright light, through which
shot out, as if from the circumference of the Moon, straight,
massive, silvery rays, seeming distinct and separate from each
other, to a distance of two or three diameters of the solar disc,
the whole spectacle showing as on a background of diffused
rose-coloured light. The silvery rays were longest and most
prominent at four points of the circumference, two upon the
upper and two upon the lower portion, apparently equidistant
from each other, giving the spectacle a quadrilateral shape.
Captain Herschel on the solar eclipse of 1871 may also be
quoted :
The sight can never be forgotten. Whether it was that my
eyes had been calmed by looking into a nearly dark field, or that
the short time—not more than a very few seconds—which was
granted me, fixed the impression received very securely, I
cannot say, but the picture formed on my retina remains
singularly clear and well defined. The corona was evidently,
to my eyes, an assemblage of distinct and well-defined groups
of rays, of which the strongest ones seemed to start directly
from the central disc, so that the so-called rifts were only the
interstices between the bundles of rays. . . . I should say
that the photographs I have seen do not recall, in any satisfactory way, the impressions which I received during those
three or four seconds, the individual, separate character of the
ray groups being almost lost.
Astronomical photography has made much progress since
the above was written, and the structure of the corona
may be learnt from the study of photographs at leisure and
their combination probably better than from the impressions
received upon the retina of the eye.
It is but just to cite one observer who found that the
corona did not realise expectations. Professor Eastway
witnessed the eclipse seen by General Myers, but not from
a mountain top, and there was some slight mist:
I was considerably disappointed (he wrote) with the appearance of the colour and brilliancy, as well as with the extreme
contour of the corona. Most observers have described the
T H E " DAILY TELEGRAPH "
14
colour as " pure " or clear white, and the light as very brilliant,
while nearly all the published sketches represent the contour
as nearly circular and regular, and the coronal rays as radial,
and equally distributed about the body of the Sun. The
colour of the corona, as I observed it, both with the telescope
and without, was a silvery white, slightly modified in the outer
portions by an extremely faint tinge of greenish violet ; and I
could not detect the least change in the colour or in the position
of the rays during totality.
The light of the corona was not brilliant—perhaps from the
effect of the haze—but appeared more like the pale light from
the trail of a meteor than anything else that I could recall at the
time. The corona seemed to be composed of two portions,
both visible to the naked eye, in which I was unable to trace
any similarity of structure. The portion nearest the Sun was
about one minute high, forming nearly a continuous band about
the Sun, and appeared to be a mass of nebulous light, resembling
in structure the most brilliant irresolvable portions of the Milky
Way. Its colour was silvery white, and, like its density,
appeared the same throughout its whole extent.
The outer portion consisted of rays of light arranged in two
different ways. In five places they were arranged into groups
resembling star-points, composed of slightly convergent rays,
but elsewhere were disposed on radial lines. The colour of the
bases of the star-points and of the radial lines was the same as
that of the inner portion, while the outer portion of the points
had a very faint greenish-violet tinge. The radial lines were
the most prominent.
These descriptions are by astronomers, knowing well what
to look for. How the magnificent and solemn spectacle
presented by an eclipse may impress a whole population with
awe is told by Arago, a distinguished French scientist, who
had opportunities to look about him at an eclipse in the
middle of last century:
At Perpignan, people dangerously ill alone remained in their
rooms. The population from early morning covered the
terraces, the ramparts of the town, and the hills outside, whence
they hoped to see the rising of the Sun. At the citadel we had
under our eyes, besides the numerous groups of citizens on
15
G U I D E T O T H E ECLIPSE
the glacis, the soldiers who were being reviewed in the vast
court.
The hour of the commencement of the eclipse approached.
Nearly twenty thousand people, with smoked glasses in hand,
examined the radiant globe, projected upon an azure sky.
Scarcely, armed with our powerful telescopes, had we begun
to perceive a little encroachment on the western border of the
Sun, when an immense shout, mixed with a thousand different
exclamations, told us that we had anticipated only by a few
seconds the observations made with the naked eye by twenty
thousand improvised astronomers. A lively curiosity, an
emulation, a desire not to be beaten, seemed to have given to
the unarmed sight an extraordinary penetration.
Between this moment and that which preceded the totality,
we remarked nothing in the behaviour of the spectators which
deserves relating. But when the Sun, reduced to a narrow
thread, began to throw on our horizon but very feeble light, a
sort of inquietude seized upon everyone; each felt the desire
to communicate his impressions to those by whom he was
surrounded. Hence, a dull roar like that of a distant sea after
a tempest.
The uproar became stronger in proportion as the solar
crescent became thinner.
The crescent disappeared ! At last, darkness suddenly
succeeded to light, and an absolute silence marked this phase of
the eclipse, as absolutely as the pendulum of our astronomical
clock. The phenomenon in its magnificence triumphed over
the petulance of youth, the careless air which some men take
for a sign of superiority, and over the noisy indifference ordinarily assumed by soldiers. A profound calm also reigned in
the air. The birds ceased to sing.
After a solemn wait for about two minutes, transports of
joy—frenzied plaudits greeted, with the same accord, the same
spontaneity, the reappearance of the first solar rays.
It will be noticed that the solar eclipses so fully described
are all old. Turn to a more recent account, and we find this :
" The clouds cleared away before the instant of totality, so
that the last thing I saw was a range of mountains to the
eastward still bright in the light; then, the next moment,
the shadow rushed overhead and blotted out the distant hills,
T H E " DAILY TELEGRAPH "
16
almost before I could turn my face to the instrument
before me."
That is the truth and the tragedy of it. The astronomer
of to-day has no time on his hands in which to witness an
eclipse. Of all onlookers, he is the one who sees least. In
other days, a solar eclipse was valued for the opportunities
it gave for correcting the Moon's place and motion; for
observing the " red flames " at the edge of the obscured
Sun, and for making drawings of the shape and appearance
of the corona. The astronomer's eye was kept steadily fixed
during the precious minutes or seconds of totality upon
what was going on in the heavens above him.
Nowadays all is changed. The camera has displaced the
eye, whether unarmed or at the end of the telescope. It has
no nerves to become excited; it gives a sure record; and
that record is permanent, to be stored up for future discussion. Professor Barnard, of the Lick Observatory, after the
fine eclipse of New Year's Day, 1889, made this confession:
" My own feelings were those of excessive disappointment
and depression. So intent was I in watching the cameras
and making the exposures that I did not look up to the Sun
during totality, and therefore saw nothing."
Furthermore, the investigation of the corona is undertaken with the spectroscope, and it is also examined with a
polariscope for analysis of the light.
Greenwich Observatory is sending an expedition, which
the Astronomer-Royal (Sir Frank Dyson) will join, to
Giggleswick, near Settle, which happens to be close by
the central line of the eclipse path in Yorkshire. Both of
the Oxford Observatories will be represented at Southport ;
Stonyhurst Observatory fortunately lies in the path of total
eclipse ; a party from the Norman Lockyer Observatory at
Sidmouth will take station farther east; whilst members
17
G U I D E T O T H E ECLIPSE
SHADOW SPOT IN ENGLAND, 6h. 2 4 m . 30s.
Mid-eclipse is simultaneous at all places on the broken line. T h e
major axis of the eclipse points in the direction of the Sun.
T H E " DAILY TELEGRAPH "
18
of the British Astronomical Association and others will be
scattered up and down the length of the shadow path.
The Solar Physics Observatory at Cambridge is sending to
Norway, where totality lasts several seconds longer. There
also American, Swedish, and Dutch astronomers will take
station.
These professional astronomers will find their time
occupied with their instruments, noticing the passing seconds
on the dial and the action of the driving clock, feeding in
and changing the sensitive photographic plates at the correct
instants, and other duties. All is done by a well-ordered
routine, in which they will have drilled themselves for weeks
or days beforehand. They will have little to tell of this
short eclipse from what they have themselves seen of it.
The " show "—the great and awe-inspiring spectacle which
Nature gives us—will be for the spectators massed outside
the limiting ropes of the different stations. They are the
favoured people.
Two centuries have passed since a total eclipse of the
Sun was visible in England; two then came pretty close
together. Clear skies favoured that of 1715, which was seen
from London under brilliant conditions, with an outflashing
corona. The eclipse of 1724, the last to have been seen in
England, was largely spoilt by floating clouds. Though
hopes be high, it may be well to be prepared for the worst
in June ; and two accounts which follow are given to show
that though cloud may spoil the astronomer's delicate
observations, there are still appearances that are both
awesome and grand.
Dr. Stukeley witnessed the last English eclipse (1724),
and though he saw nothing about the Sun at the total phase,
he says the spectacle was incomparably solemn. Darkness
was total and palpable, and spread over the observer from
19
G U I D E T O T H E ECLIPSE
the south " like a great black cloak," or like a curtain drawn
across from side to side. It was immediately preceded by
livid tints on the Earth and in the sky, while the whole aspect
of things was awful in the extreme, and " seemed to announce
the death of Nature."
An eye-witness of the cloudly eclipse of 1851, Mr. W. Grey,
remarked that " as the shadow approached the clouds
appeared in violent motion, from the fluctuations of the
shadows on them, and darker purple overhead than the
darkest thunder cloud; in the horizon lurid yellow and
orange. In the north-west was an opening into the clear
sky, which suddenly changed from a misty blue into the
most lovely celestial blue, and this darkened to indigo.
What injury the clouds caused to the astronomical observations was compensated by the strange horror they added
to the scene."
The effect of an eclipse shrouded in cloud has been well
described by Mrs. Mabel Todd, who accompanied Professor
Todd to Japan for the eclipse of 1887. A dense body of
cloud, she says, silently massed as totality approached:
Finding that my drawing of the outer corona would be
impossible, from the rapidly thickening sky, I left my appointed
station and hastened to the upper castle wall to watch the
changed landscape under its grey shroud. Even inanimate
things are at times endowed with a terrible life of their own, and
this deliberate, slow-moving pall of cloud seemed a malignant
power not to be eluded.
Now and then a flood of sunlight fell upon the smoking and
disastrous crater of Nasu-take — a spectacle both aggravating
and sublime.
Totality was announced, and as if by two or three jerks the
darkness fell. Silence like death filled castle and town and all
the country round. Except the feeble glimmer of a few lanterns
in the town, 80 feet below, a streak of strange, sulphurous
yellow in the south-east seemed to give out the only light in
the world.
T H E " DAILY TELEGRAPH "
20
Not a word was spoken. Even the air was motionless, as if
all nature sympathised with our pain and suspense. The
useless instruments outlined their fantastic shapes dimly against
the massing clouds, and a weird chill fell upon the Earth.
Mountains and rice-fields became indistinguishable, the clouds
above us turned nearly black, and a low roll of thunder muttered
ominously on the horizon towards Kuroiso.
All trace of colour fled from the world. Cold, dull, ashen
grey covered the face of nature.
Even in that supreme moment my thoughts flew backward
over the 8,000 miles of land and stormy ocean already travelled,
the ton of telescopes brought with such care, the weeks of
patient toil and constant observation at the old castle in a
remote Japanese town—all the long journey and elaborate
preparation, chiefly for just these three minutes of precious time
now slipping away so fast.
And already they are gone. The rare corona has wasted its
ever new glories upon the hither side of the uncaring clouds.
We had trusted Nature ; she had failed us, and the prevailing
mood was a sense of overwhelming helplessness.
The crowd of friends, Japanese, English, and American,
breathed one mighty sigh, as from a universal heart just relieved
of tension near to breaking. Then some one spoke, and we
faced common life again.
No such misadventure as this, let us hope, will attend the
English eclipse of the 29th June. Given a clear sky, the
observer should find much to divide his attention in the
moments just before totality. As growing darkness comes
on, and before the shadow strikes the land about him, if he
looks up he will see the crescent of the Sun reduced to the
merest wisp, itself about to be extinguished. It is likely that
the phenomena known as " Baily's Beads " may then be
witnessed. As the crescent narrows, it seems to be crossed
by thin black lines, which may widen and give the appearance of bright beads. These thin lines are obvious in a
field-glass, and have been seen by a keen eye unassisted,
looking specially for them. The beads run together like
contiguous drops of water before disappearance.
21
G U I D E T O T H E ECLIPSE
It is an optical effect, that not only has been seen by the
eye, but has been photographed. The cause is obscure, but
" Baily's Beads " have been said to be due to the irregular
surface of the Moon about its edge, the lunar mountains
projected against the bright solar crescent creating divisions
in its light. It is very doubtful whether this is the true
explanation.
A mere 22-24 seconds in June will give small opportunity
for witnessing anything beyond the actual eclipse. All eyes
will, it is safe to say, be fixed upon the darkened Sun and its
brilliant surroundings—except, of course, those of the luckless
astronomers, the slaves of their instruments. On any clear
night take out your watch, with the hand that times the
seconds racing round the dial, look up at the familiar heavens
while 24 seconds run their course, and it will at once be
realised how short is the time for spying out forms and
details and receiving impressions. An eclipse is unfamiliar.
If one were strong-minded enough to turn one's back upon
the big spectacle—it is not recommended—there would be
things to see and to be remembered.
The approach of the shadow has been mentioned. Before
this occurs, there is a pretty spectacle often observed, when
sunlight filtering through the leaves of a shady tree casts
little crescents of light upon the ground, each one an image
of the partially eclipsed Sun; but on this occasion the Sun's
altitude will be too low to give this phenomenon.
Sometimes noticed is the appearance of wavy shadow
bands. The sunlit side of a whitewashed cottage, or a
white sheet spread upon the ground, shows them best. Over
such a surface they flitter with a rapid wave-like motion,
narrow bands of alternative shade and light, keeping parallel
and never still. They occur only in the minutes before and
after total eclipse. They cannot be associated with the
T H E " DAILY TELEGRAPH "
22
Moon's shadow, their apparent motion being slower and
also variable. The width of the shadow bands will vary at
different eclipses. It is probable that they are due to
flickering of the slender beams of light from the waning or
waxing Sun's crescent, produced by undulations in our
atmosphere, in the same way that the familiar twinkling of
the stars is produced. They appear to be racing away, at
speeds that have been variously likened to that of a man
SHADOW BANDS AT ECLIPSE.
running and of an express train. In fact, they have no
progressive motion. It is an optical effect, due to the wavelike, up-and-down movement of the bands.
Not alone in man and in inanimate nature are the effects
of a solar eclipse to be noticed. Animals are quickly
responsive to the almost sudden onfall of darkness, and not
infrequently are terrified. At an eclipse that was almost
but not quite total, the central line passing across England
from Dorset to Lincoln in 1858, it was remarked that rooks
and starlings took flight in flocks to their night quarters.
Cows and horses will cease to graze, and grasshoppers become
quiet. At the Perpignan eclipse experiment was made with
23
G U I D E T O T H E ECLIPSE
a dog that had been kept from food for twenty-four hours.
Just before totality he was thrown bread, which he began to
devour ravenously. At total eclipse he dropped it, evidently
frightened. Totality lasted over two minutes, but not until
sunlight again came would the creature return to the food.
M. Laussedat, who observed an eclipse in Algeria, relates
this fact: " The plants showed how rapid is the action of
light, which they receive as by a kind of diffused sense in
their corollas ; for, in spite of the short duration of totality,
daturas, convolvuli, poppies, and nightshades, which had
been closely shut, were observed to half open during the
total eclipse."
In China and India and other Eastern countries an eclipse
is still a subject of terror, and the more ignorant people
prostrate themselves and beat gongs to ward off the evil.
The Chinese peasants believe that at eclipse a great celestial
dragon possessing very black claws extends them to seize
the Sun and Moon.
A resident of Fort Sill, Indian
Territory, U.S.A., relates an amusing incident that occurred
at the eclipse of 1878:
On Monday last we were permitted to see the eclipse of the
Sun in a beautiful bright sky. Not a cloud was visible. We
had made ample preparation, laying in a stock of smoked glass
several days in advance. It was the grandest sight I ever
beheld, but it frightened the Indians badly.
Some of them threw themselves upon their knees and invoked
the Divine blessing; others flung themselves flat on the ground,
face downward; others cried and yelled in frantic excitement
and terror.
Finally one old fellow stepped from the edge of his lodge,
pistol in hand, and fixing his eyes on the darkened Sun mumbled
a few unintelligible words, and raising his arm took careful aim
at the luminary, fired off his pistol, and after throwing his arms
about his head in a series of extraordinary gesticulations,
retreated to his own quarters. As it happened, that very
instant was the conclusion of totality. The Indians beheld the
G U I D E T O T H E ECLIPSE
24
glorious orb of day once more peep forth, and it was unanimously
voted that the timely discharge of that pistol was the one thing
that drove away the shadow and saved them from the public
inconvenience that would certainly have resulted from the
entire extinction of the Sun.
NOTE
U S E F U L W O R K FOR AMATEURS
It would be helpful for scientific p u r p o s e s if t h e precise b r e a d t h
and position of t h e shadow track, at its limiting lines and centrally,
could be fixed by observations taken at different places along t h e
lines. H e l p will be given by those w i t h i n t h e shadow zone if t h e
d u r a t i o n of totality is recorded, by n o t i n g t h e exact n u m b e r of
s e c o n d s — p e r h a p s w i t h even a fraction of a second a d d e d — t h a t
elapse between t h e instant w h e n t h e lower left-hand edge of t h e
S u n i s covered u p , and t h e instant w h e n t h e u p p e r r i g h t - h a n d
edge is u n c o v e r e d . S o m e self-sacrifice m u s t be entailed by
m a k i n g these precise time observations, for it will be necessary to
concentrate attention u p o n t h e time-keeper and visually on t h e
edges of t h e S u n , to t h e exclusion of a general view of t h e corona.
T h e l u n a r tables to-day are m o r e accurate than they w e r e i n the
year 1715, w h e n a total eclipse of t h e S u n was visible in E n g l a n d .
F o r that occasion E d m u n d Halley (afterwards Astronomer-Royal)
a d d e d to a m a p of t h e predicted s h a d o w track across t h e c o u n t r y
t h e following instruction :
" N . B . T h e C u r i o u s are desired to O b s e r v e it, a n d
especially t h e d u r a t i o n of T o t a l D a r k n e s s , with all t h e care
they c a n : for t h e r e b y t h e situation and dimensions of t h e
shadow will be nicely d e t e r m i n e d , and by m e a n s thereof we
m a y be enabled to Predict t h e like A p p e a r a n c e for ye future
to a greater degree of certainty t h a n can be p r e t e n d e d to at
p r e s e n t for w a n t of such O b s e r v a t i o n s . "
M a n y persons did c o m m u n i c a t e to Halley their observations
m a d e in various parts of t h e k i n g d o m , and from these d a t a he was
able to lay d o w n t h e actual p a t h of t h e shadow as observed. T h i s
differed s o m e w h a t from t h a t p r e d i c t e d . F o r e x a m p l e , Scarb o r o u g h , w h i c h h a d been on t h e n o r t h e r n limit of t h e predicted
track, was found to have been well outside the track. R o c h e s t e r ,
w h i c h was p r e d i c t e d to be several miles outside t h e shadow p a t h ,
p r o v e d to be within it.
T h e corrections of t h e l u n a r tables derived
from these observations a p p a r e n t l y enabled Halley to m a k e
i m p r o v e d predictions for t h e next English eclipse of 1724.
II.
WHY AN ECLIPSE OCCURS
It cannot exaggerate to say that millions of our people will
be watching the total eclipse of the Sun on the morning of
the 29th June next. The spectacle, as before stated, is one
that no Englishman has seen in his own country for
200 years past, so rare is it for the shadow to fall upon
this small group of islands. It will not be repeated here till
the 11th August, 1999, when the shadow path crosses the
Land's End area of Cornwall. As the child of five to-day
will then be in his 78th year (possibly 79th), there can be few
who will be able to store recollections of both eclipses.
If a shadow path were purposely to be chosen which would
bring the spectacle before the densest populations, one could
hardly (London excepted) map out a path more suitably
situated than that of the 29th June.
Liverpool and Birkenhead lie just within the area of total
eclipse, and together can turn out over three-quarters of a
million people. The shadow passes over the dense industrial
area of Lancashire, engulfing Blackburn, Preston, Bootle,
Accrington, Clitheroe, and many smaller towns, with St
Helens, Bacup, and Wigan near by the limiting line; then
crosses Yorkshire in a northerly direction, with Settle,
Leyburn, and Richmond all centrally placed ; and in Durham
it will encompass Darlington, Stockton-on-Tees, Middlesbrough, and the Hartlepools, with Sunderland and Saltburnon-Sea at the limits of another industrial area.
And everything depends on the weather that morning;
upon the fortune of clear skies in a period of 22-24 seconds
during which total eclipse lasts. A little cloud, or mist
hovering over town or countryside before the Sun has had
time to reach high altitude, will be sufficient to spoil the
25
T H E " DAILY TELEGRAPH "
26
greatest effects. That is a chance which attends every
solar eclipse.
Late June, with warm, short nights, is one of the most
favourable times on which to expect fine mornings.
Attention by our own countrymen will naturally be concentrated upon the path of the shadow where it crosses this
small island, and a word of advice to those whose homes
happen to be about the limits of the path will not be wasted.
Let them take train or motor-coach, and get as near as
possible to the central line—15 miles distant. At the
shadow's limits they can see total eclipse but for a moment,
and may see nothing of it. There are certain errors in the
tables of the Moon which add to the difficulties of plotting
the exact path of the shadow, and the best computations may
be in places a mile out.
The shadow, after its rapid flight over England, has still
some thousands of miles more of the Earth's surface to
traverse before it leaves Earth. It falls, a long elliptical spot,
first on the Atlantic Ocean, a little south-west of Ireland.
Anyone out upon the ocean at that place will see the Sun
rise already at mid-eclipse.
The shadow spot touches land where Carnarvonshire juts
out a promontory into the St. George's Channel. Criccieth
is the first small town over which the shadow sweeps centrally.
Our highest mountain, Snowdon, will be engulfed in it as
it crosses North Wales, and its summit would be a favourable
place from which to watch the flight of the shadow as it
darkens in succession the neighbouring mountain tops and
valleys, could there be any assurance that Snowdon would
not be itself concealed in the mists that are so frequent
there at morning. There can be no such assurance, and the
spectator anxious to take his best chance, of seeing the total
eclipse will do well to avoid Snowdon. Yet an adventurer,
27
G U I D E T O T H E ECLIPSE
T O T A L ECLIPSE OF S U N .
In area on which shadow spot falls, Sun is totally eclipsed.
within penumbra partial eclipse.
Elsewhere
daring all in an early morning climb, might be rewarded with
the view of a lifetime.
Southport lies central upon its path as the shadow reaches
English land in Lancashire, the Sun being then risen to an
altitude of 11½ degrees. The shadow speeds along over that
county and over Yorkshire and Durham, to reach the North
Sea at Hartlepool.
Continuing its journey across the waters at the same
T H E " DAILY TELEGRAPH "
28
ANNULAR ECLIPSE OF S U N .
Annular eclipse visible only on central line. Elsewhere within
penumbra partial eclipse.
terrific pace, the shadow touches land again on the coast of
Norway, with Stavanger central. Norway, Sweden, and
Lapland are traversed in a north-easterly direction, then the
line passes out to and over the Arctic Ocean and inaccessible
parts of north-eastern Siberia, and finally the shadow leaves
the Earth among the Aleutian Islands. In its easterly trend
the shadow spot slightly broadens out, and in Scandinavia,
in place of England's 22-24 seconds of total eclipse, astro-
29
G U I D E T O T H E ECLIPSE
nomers will have 40-44 seconds of totality. The longest
period of totality at this eclipse is in the Arctic, 50
seconds. (See map on p. 60.)
The reasons why an eclipse occurs can be briefly explained.
As on a bright summer day one walks in the direction of
the Sun, one's dark shadow follows, trailing behind. The
Moon, a solid spherical body, also casts its dark shadow,
which trails behind it into space. The Sun's diameter is
very much greater than that of the Moon, and necessarily
the shadow projected into space by the Moon must take the
form of a cone tapering to a point.
The same is true of the Earth, a spherical body.
It is
larger than the Moon, and its tapering cone of shadow
projected into space is consequently larger and longer
than the Moon's.
We do not see the Moon s trailing shadow save at times
of total eclipse of the Sun, when that shadow falls upon the
Earth. If this world of ours had no atmosphere, and interplanetary space was dusty with particles reflecting sunlight,
then as we looked into the heavens we should see the shadow
projecting behind the Moon and travelling with it, by the
cutting off of sunlight from the dancing atoms in the shadow
cone.
We do not see the Earth's trailing shadow against the sky
faintly illuminated by the stars, unless, indeed, twilight
is to be associated with it. The darkness at night tells
us that we are ourselves immersed in the shadow. Occasionally the Moon, in its monthly circuit around the Earth,
passes into and travels across the cone of dark shadow thrown
back by the Earth into space, and then there is a lunar
eclipse. Rarely, indeed, is the Moon actually lost to sight
during eclipse, because some sunrays when passing through
our atmosphere are bent inwards upon it; but the strong
Ε.
SOLAR
CORONA,
1900,
Royal
TWO
GROUPS
OF
Ε.
Barnard.
MAY 2 8 .
SUNSPOTS.
Observatory,
Greenwich.
T H E " DAILY TELEGRAPH "
30
white light of Full Moon fades almost to nothing while the
satellite is in the Earth's shadow.
Always it is new Moon at times of solar eclipse, for the
Moon is then in line between Earth and Sun ; and the Moon
is invisible in the sky until it comes exactly into place to
cover up the round solar disc from our sight. Then—and
not before or after—it appears as a dark globe. Much
misconception is due to drawings of an eclipse in progress
which represent the Moon as a black sphere passing upon the
bright Sun. The dark hemisphere of the Moon turned
towards us would appear as a black disc, could we see it.
What we do see in the partial phases till the eclipse is near
totality is not the Moon, but the blue sky right up to
the sharp edge of the crescent Sun—an effect due to the
scattering of light by particles in our atmosphere.
Always it is full Moon at times of lunar eclipse, for the
Moon is then in line with the Sun behind the Earth.
Obviously in each of its monthly journeys around the
Earth the Moon must pass between Earth and Sun, and also
must pass behind the Earth into proximity with the Earth's
shadow. There should, then, be both a solar and a lunar
eclipse each month; and there would, in fact, be these
monthly eclipses were the bodies moving in the same
plane, which they are not.
Let us think of the Earth's path round the Sun as level.
A round table top will serve for illustration. Its surface is
level. A ball placed in the centre may stand for the Sun,
and a marble moved around the table rim would represent
the Earth on its travels. In like manner the Moon, on its
smaller path, moves around the Earth. In both cases as
seen from above the direction of travel is opposite to that
in which the hands of a watch travel.
But the Moon's path in our illustration is not level, but
31
G U I D E T O T H E ECLIPSE
is tilted. It is on a different plane to the Earth's. It is
just that tilt which denies us the spectacle of monthly
eclipses. Often it must happen that the Moon, when
moving in that half of its tilted path which is above the level
plane of the Earth's orbit, must, as seen from Earth, pass
T I L T E D PATH OF THE M O O N .
above and clear of the Sun's round face. When the Moon is
below the level plane, often it must pass below and clear of
the Sun. In neither case can there be an eclipse of the
Sun.
The same conditions apply to a lunar eclipse. The Moon
upon its path often passes above or below the cone of dark
shadow thrown back into space by the Earth, and there is
no eclipse.
Only at such times as the Moon is in places where the
planes cross—or, in other words, when Sun, Moon and
Earth are in a straight line—can there be an eclipse. There
is some margin to this statement, which would be precisely
true if the three bodies were points. But because the Earth
is of some size, even if the centre of the Moon is somewhat
out of line with the centres of the two other bodies, the
shadow cone it throws may fall somewhere on the Earth,
giving total eclipse.
It may just fail to do this, but the Earth, or part of it,
may fall within the penumbra, or outer shadow. In that
case there will be partial eclipse.
Similarly for a lunar eclipse. Since the shadow cone
thrown by the Earth is of considerable thickness, and a
section of it at the distance of the Moon is a circle two or
three times as large as the Moon's disc, it follows that the
T H E " DAILY TELEGRAPH "
32
Moon, even if it passes through the shadow cone some
distance from the central line, will still suffer eclipse.
So eclipse comes about not only when the Sun, Moon
and Earth are all in the exact line in which the planes of
the Earth's and the Moon's paths intersect, but also when
they are in a line which is slightly in advance of, or
behind, that line in their orbital progression. The distance
defining the points between which an eclipse either of Sun
or Moon is possible may be referred to as the " eclipse
limits" (traditionally " e c l i p t i c " limits).
A certain number of eclipses—rarely total—happen in
every year. There must be at least two, both of the Sun,
and there may be as many as seven. They occur at two
THEORY OF ECLIPSE LIMITS.
When the New Moon is at any of these places on her path total solar
eclipse may take place.
seasons of the year, sometimes called the eclipse months,
which are separated by something less than six months, so
that eclipses happen earlier each year than in the one preceding. An eclipse is followed after an interval of eighteen
years by another associated with it, falling ten or eleven
days later in the year, visible in the case of solar eclipse
from places on the Earth nearly in the same latitude, but
separated by a third of the globe in longitude. Thus
the eclipse of the present year had a precursor on the
17th-18th June, 1909, and will have a successor in the
eclipse " family," as it is termed, eighteen years hence.
33
G U I D E T O T H E ECLIPSE
It may still seem strange that a body so small as our Moon,
with a diameter of but 2,160 miles (roughly one-fourth that
of the Earth), should completely blot out the vast mass of the
Sun, if only for these 22-24 seconds. It would not do so
but for the fact that it is so near to us ; the average distance
of Moon from Earth is only 239,000 miles. The Sun's
diameter is 864,000 miles. It is difficult indeed to convey
an idea of the immensity of the mass of the Sun. Figures
do not give it. We may get some help by a comparison
with our own satellite on its travels.
The Moon, although near as astronomical distances are
measured, is obviously a long way off. Out in the sky it
looks a long way off. Between us is a vast void of space.
The theatre, to minds accustomed to terrestrial measurements, is so vast, and the Moon so far away, that although
our satellite moves with a velocity that would leave our
most rapid cannon shot crawling along at what would seem
a snail's pace hopelessly behind, yet it takes nearly the full
calendar month for the Moon to make a complete circuit of
the Earth.
If in fancy we place the Earth at the centre of the Sun's
disc, with the Moon travelling round the Earth, then the
path of the Moon is only large enough to extend about halfway out to the edge of the Sun's disc. The true proportions
are shown in the diagram overleaf.
Or, to use the illustration another way, if we imagine
the Sun as a hollow ball, and place the Earth at its centre,
then the Moon would go on circling round the Earth inside
the Sun, with still an immensity of space before the Sun's
limits were reached.
The Sun's diameter is four hundred times larger than that
of the Moon. But the Sun is removed from us (in round
figures) four hundred times the distance of the Moon. So
T H E " DAILY TELEGRAPH "
34
SIZE OF THE S U N .
Ample space would exist for the Moon to continue to move on its present
path round the Earth were Moon and Earth to be placed in the
interior of the Sun.
against the background of the sky the two bodies appear to
be of exactly the same size, and an instrument of precision
is necessary to distinguish any difference between them.
Solar eclipses are calculated by astronomers long before
they take place. The reader who looks into almanacs or the
scientific papers for announcements of them must often have
noticed the words " invisible at Greenwich " (or some other
place). Or he may have found the words " visible as a
partial eclipse at Greenwich " and within an area stated.
For instance, there will be another eclipse of the Sun this
year in December, but no one takes any concern in it, for
G U I D E T O T H E ECLIPSE
35
it is merely partial (about one-half), is invisible at Greenwich, and can be seen only from the southern area of South
America and from the South Pacific Ocean.
As the Moon is smaller than the Earth, and its shadow
takes the form of a cone tapering to a point, obviously it
cannot entirely eclipse the Earth. Or, to express it another
way, a solar eclipse is not visible over the whole of the Earth.
The total phase can be seen over only a very small area of
the Earth indeed, along a track which may extend in length
to thousands of miles, but can have no considerable breadth.
The shadow path traced in Wales and England on the
29th June measures only 30 miles across. It has been
calculated that in the most favourable circumstances the
shadow spot may have a diameter of 167 miles. Such a
shadow spot, were it to fall upon England, would trace a
black band of darkness extending across from the English
Channel as far north as the line Aberdovey to Lincoln,
engulfing the whole of the southern and midland counties,
and more than one-half of the territory of England and
Wales—very different from our little 30-mile track in
June.
The total eclipses of the Sun that have been visible in
different parts of the British Islands during the past five
centuries (with three years thrown in) have numbered but
six in all, in the following years:
1424, June 26.
1433,
1598,
*1652,
*1715,
*1724,
June 17.
Feb. 25.
April 8.
May 3.
May 22.
* New Style.
T H E " DAILY TELEGRAPH "
36
Two elements enter into the determination of the size of
the shadow spot, beyond the effect of the altitude of the Sun.
The size of the Sun as seen in the sky itself varies. The
path of the Earth round the Sun is not circular, but is
elliptical. When, with the Earth as our coach, we are
carried along from a distant part of its path to a place
January
1
June 29.
VARIATIONS IN APPARENT SIZE OF SUN'S DISC.
nearest to the Sun, the luminary, being nearer, must
appear in our eyes larger. As we are carried away to our
greatest distance from the Sun, it must appear smaller.
Earth is at its farthest distance from the Sun in the English
summer, and on the 29th June, accordingly, we have the
smaller Sun.
These variations, however, being small, may be disregarded for our present purpose. Of more concern to us
is the variation in the apparent size of the Moon.
The Moon's path round the Earth also is not circular, but
is elliptical. Accordingly the Moon's distance varies. A
fortnight hence it may either be farther from us or nearer to
us than it is to-day, and its apparent size will then be smaller
or greater as the case may be. It happens that on the
29th June the Moon is at a part of her path rather far from
us—but not at its farthest. The shadow does little more
than just touch the Earth, and totality is short.
37
G U I D E T O T H E ECLIPSE
For that we may be at least thankful. Had the Moon on
this coming occasion been withdrawn a little farther distant
than it is, then we could not have had total eclipse. Instead,
there would have been witnessed an annular eclipse. That
is to say, the Moon as we saw it in the sky would have been
too small entirely to have covered up the Sun's bright face,
ANNULAR ECLIPSE OF S U N .
Moon too small to cover the Sun's face.
and at the greatest phase there would have been visible a
narrow ring of bright sunlight around the Moon. In
those circumstances nothing of the corona would be
disclosed, and with that outstanding feature missing the
eclipse, as a popular spectacle, would count as a sad
disappointment.
On the other hand, we might have had a much better
eclipse than that now awaited. As astronomers value these
events, the solar eclipse of 1927 is a remarkably poor one.
It gives no sufficient time for the many observations they
would like to make. Had it happened that the Moon was at
the part of its path nearest to us, not only would the shadow
spot touching Earth have been much larger, but the duration
T H E " DAILY TELEGRAPH "
38
of total eclipse, instead of these 22-24 seconds, would have
lasted over minutes. The longest possible duration of solar
eclipse, seen from the Earth at noon from a point on the
equator, has been found by mathematics to be a few seconds
short of eight minutes.
An eclipse during which totality occurs for almost the
maximum possible duration—namely, 7 minutes 28 seconds
—is predicted for the 5th July, 2168. A long eclipse that
should have favoured scientific observation was that of the
18th May, 1901, when at Sumatra the Sun was obscured
for 6½ minutes. Unfortunately for the astronomers who
travelled thousands of miles to establish a station there,
clouds somewhat interfered, and the results were not of firstclass importance. At an eclipse watched from India in
1868, totality lasted 5½ minutes. This time has been
approached more recently, the eclipse of 1883 having given
totality for 5 minutes 23 seconds. Two other eclipses, those
of 1919 and 1922, spent the long totality of 6 minutes in midocean, and both were observed from places at the ends of
the line where duration was somewhat less.
It is rare, however, for total eclipse to last longer than
from 3 to 4 minutes. In the past half-century, allowance
being made for eclipses that have been spoilt by clouds,
astronomers have enjoyed in all about three-quarters of an
hour for their work.
Thus far attention has been wholly given to the Moon's
true shadow, to the dark shadow that falls upon Earth,
ignoring all else. That course seemed best to adopt, in
order to avoid confusion. The dark shadow—the important
one—is called the umbra. There is a secondary, or false
shadow, named the penumbra, the creation of which the
diagram explains. In all the area over which the penumbral
shadow falls a portion of direct sunlight is cut off, but except
G U I D E T O T H E ECLIPSE
39
PARTIAL ECLIPSE OF S U N .
Umbra passes clear of Earth.
Partial eclipse where penumbra reaches
Earth.
at places comparatively near to the line of total eclipse
the loss of illumination, proceeding slowly, will be little
noticeable.
Earth begins to enter the penumbral shadow at the
moment when the eye, looking upwards, detects the first
contact of the Moon with the Sun. There is no visible
change in the landscape or in the sky when contact with the
T H E " DAILY TELEGRAPH "
40
penumbral shadow occurs, and the area it covers upon
Earth can only be determined mathematically.
It follows that at all places within the area of the penumbral
shadow partial eclipse will happen. The occurrence of the
29th June will be witnessed as a very large partial eclipse
over the greater part of the British Isles and in northern
countries of the Continent. London, though lying 180 miles
London, 6h. 20m.
Edinburgh, 6h. 28m.
GREATEST PHASE OF PARTIAL ECLIPSE.
south of the line of totality, will at about mid-eclipse
see the Sun obscured for all but the tiniest crescent on
the lower portion of the Sun's disc. Allowing 100 parts
for the Sun, of these no fewer than 96 will be covered by the
eclipsing Moon. Edinburgh, and other places north of the
line of totality, will find the visible thin crescent of the Sun
on the upper part of the disc.
For the information of those who are unable to travel into
the shadow path, a table giving the proportions of the partial
eclipse as it will be seen from different towns is printed on
the opposite page.
It is, if the phrase may be permitted, a piece of remarkable
good fortune that the Moon moves upon its path where it
G U I D E T O T H E ECLIPSE
41
does. For had our satellite been withdrawn but a few
tens of thousands of miles farther from the Earth it would
not have been large enough to give total eclipse of the Sun,
the dark shadow could not have touched Earth, and the
human race might never have known of the existence of the
" red flames " seen during eclipse at the Sun's edge, nor of
the brilliant, far-spreading corona. Certainly it could never
have hoped to witness the spectacle to be presented, if clear
skies favour us, on the 29th June.
PARTIAL
(Sun
100 parts.
ECLIPSE
Of these there will be eclipsed at the
greatest phase at—
Parts.
Bedford . .
Birmingham
Brighton
Bristol . .
Cambridge
Cardiff
..
Carlisle . .
Chester . .
Derby
Dover
Edinburgh
Exeter
Glasgow . .
Gloucester
Hereford..
Hull
Ipswich . .
Isle of W i g h t
Leeds
Leicester..
Lincoln . .
97
98
95
98
97
98
99
99
98
95
98
97
97
98
98
99
96
95
99
98
98
London . .
Manchester
Newcastle
Northampton
Norwich
Nottingham
Oxford . .
Plymouth
Sheffield
Shrewsbury
Southampton
Stafford . .
Truro
Worcester
Yarmouth
York
Isle of M a n
Armagh . .
Belfast . .
Cork
Dublin
..
Parts
96
99
99
97
96
98
97
97
99
99
96
99
97
98
96
99
99
97
97
98
98
Altitude is given at eclipse to indicate the height of the
Sun above the horizon. The Sun's altitude at the approaching eclipse is unfortunately low; as the spectacle is seen along
the shadow path over North Wales and England, not more
T H E " DAILY TELEGRAPH "
42
than 10 to 13 degrees. There is a ready means of roughly
estimating the measure of a degree. The Sun's disc has a
diameter of just about half a degree. Accordingly, if we
ALTITUDE OF SUN AT THE ECLIPSE.
imagine twenty to twenty-six Suns piled up one upon another
from the horizon, that will give the Sun's height.
When distorted near the horizon, the bright Sun appears
in our eyes to be actually larger than it is.
Total eclipses of the Sun in the remote past are of considerable importance chronologically. None understanding
them, it was but natural that they should strike terror.
Given a record of some great event in progress when it
happened that eclipse occurred, and the place, and we can
43
G U I D E TO T H E ECLIPSE
calculate back to find when an eclipse was visible at that
place, and so fix the year and day. Notable among historical
eclipses is that mentioned by Herodotus as occurring during
the war between the Lydians and the Medes. A fierce
battle was being waged and of a sudden ceased, the father of
history assigning the cause to an instant turning of day into
night. So awe-stricken were the contending forces by this
sign of wrath from the heavens that they would fight no more,
but immediately concluded peace, which was cemented by
two intermarriages arranged between the foes.
The date of the battle and peace can confidently be stated
as the 28th May, 585 B.C. It was the first eclipse to be
predicted, by the great physical philosopher, Thaïes of
Miletus, who is credited with having given the year.
The Chinese were the first to preserve records of eclipses,
and one of these which goes back into the pre-Christian era
is of unique interest. Chung K'ang, fourth Emperor of the
Hsia dynasty, reigned in China. There was the imperial
astronomer Hi. Also there was a second imperial astronomer, Ho. It was their business to attend the celestial
orbs. It all makes sad reading in the great book of the
" Shu Ching." An eclipse occurred, and Hi and Ho were
unprepared. They should have performed the rites appropriate to such an occasion, such as shooting off arrows and
beating upon drums and gongs with the object of frightening
away the monster from the Sun that it was endeavouring to
devour. At the dread moment Hi and Ho were found
intoxicated and incapable of duty, and great was the confusion prevailing in that Royal Court. Chung K'ang
ordered their instant decapitation. Thus he enforced the
great truth that the heavenly bodies, like British Admirals,
wait for no man's pleasure.
Astronomers have at times faced grave perils in order to
T H E " DAILY TELEGRAPH "
PHASES OF PARTIAL ECLIPSE, JUNE 29.
Progress Right to Left.
45
G U I D E TO T H E ECLIPSE
observe an eclipse. Janssen, a famous Frenchman, was in
beleaguered Paris during the Franco-Prussian War in 1871,
when the military lines were drawn so strongly around the
capital that it seemed impossible that anyone should leave it.
Undaunted, he rose from Paris in a balloon on the 2nd
December, taking with him a young sailor as an assistant,
and also the essential parts of a reflecting telescope. A
light breeze carried the balloon to the mouth of the Loire,
where the aeronauts descended. The daring Janssen
obtained an interview with Gambetta, who gave him friendly
aid and encouragement, and he took his station at Oran.
The reward of so much effort was pitiful ; clouds completely
covered the sky and observation was hopeless.
The disappointments that astronomers have to face with
such good grace as they can command are well illustrated by
this eclipse. Sir Norman Lockyer journeyed from England
to Sicily, was shipwrecked on the way, and amid drifting
clouds obtained a glimpse of the corona for just one second
and a half. Three parties which climbed Mount Etna to
different heights saw absolutely nothing.
In Russia Professor Mendeleef had a more alarming
adventure at the eclipse of the 19th August, 1887. He would
have no defeat by clouds. He would use a balloon as his
observing station, and it should carry him above them. It
did. The arrangement was for an aeronaut to accompany
the astronomer, but when both were in the basket the overweighted balloon refused to ascend, and by some mischance,
while the load was being lightened, the aeronaut was left on
the ground. Mendeleef shot up alone into space, reaching
the dizzy altitude of 11,500 feet—two miles above the Earth.
In fact, he did enjoy a fine and unobstructed view of the
corona, which was obscured to those watching from below,
but what with his difficulties in amateur management of the
T H E " DAILY TELEGRAPH "
46
unsteady balloon and fear that he might never reach ground
alive, he had afterwards little to tell that was of any scientific
value.
Father Stephen Joseph Perry, S.J., the Director of Stonyhurst College Observatory, near Blackburn, Lancashire,
was a martyr to scientific duty. At the eclipse of the
22nd December, 1889, he led one of the two English expeditions organised by the Royal Astronomical Society, choosing
as his station the unhealthy Iles du Salut, off the coast of
French Guiana. His observations there were the last effort
of a dying man. Stricken with malaria, he crawled to the
hospital as soon as the eclipse was over, and expired five
days later, at sea, on board the Comus. His body was buried
at Barbados. Misfortune throughout attended this fated
eclipse. Clouds altogether obscured the Sun in Africa, and
though Father Perry from his island off South America
obtained some photographs when the skies for moments
opened, his plates suffered grave deterioration from the
climate and from inevitably delayed development.
A suggestion has been advanced to employ aeroplanes at
the approaching eclipse. The fast-moving platform would
make this course useless for the ordinary scientific observations, which require stability ; but observers flying at a great
height in the shadow should be able to enjoy a good view
of the corona, and especially of the long and elusive
" streamers "—if any are visible—rays that at certain
eclipses watched from mountain heights have been seen to
extend outwards from the Sun many millions of miles.
Of recent years an additional use has been found for
eclipses of the Sun, not lacking in novelty. Einstein's
Theory of Relativity required that light should be subject
to the force of gravity, a quality that hitherto has been denied.
That is to say, a light ray coming from a great distance, if it
47
G U I D E T O T H E ECLIPSE
happened on its journey to pass near a large body, should be
deflected towards that body by the latter's gravitational force.
The difficulty has been to find a theatre large enough for
the test.
The announcement of Einstein's theory again directed
attention to this long-sleeping problem as old as Newton. A
solar eclipse gave the opportunity of solving it. Light from
a star seen in the close neighbourhood of the eclipsed Sun
must pass near the Sun in its journey towards Earth. If the
ray of starlight was, in fact, deflected by the presence of the
Sun's mass, then that deflection would be made evident by
a displacement away from the Sun of the star's apparent
position in the vault of the heavens.
The method of practical test was to photograph at night
the part of the heavens against which the eclipsed Sun would
lie several months before eclipse. Then at eclipse the same
area was again photographed, the stars in the darkened sky
around the eclipsed Sun leaving their images on the sensitive
plates. Two British expeditions were sent out at the eclipse
of the 28th May, 1919, to undertake the test. Measurements
on the plates disclosed an actual small displacement in the
stars' positions, thus confirming Einstein's theory.
Wireless experiments will be undertaken at the approaching eclipse, with a view to determining whether eclipse has
the same effect on the waves as night. Some differences in
reception from stations within and outside the shadow track
were noticed at the American eclipse of January, 1925.
It is anticipated that time-signals will be broadcast, in
what form is not known ; but if the Greenwich clock could
issue its seconds with an occasional break for numeration,
nothing better could be desired for time observations.
III
T H E SUN'S S U R R O U N D I N G S
T H E Sun's surroundings can never be understood without
some little knowledge of the Sun itself. Its mass is not
easily conveyed to the mind. It is so vast that the gravitational force exerted by the Sun keeps the whole system of the
planets, of which the Earth is one, in control. And the Earth
is among the planetary group moving nearest to the Sun—
not quite 93 millions of miles (mean) separates the two
bodies. Outer planets like Neptune and Uranus move at
distances of 2,800,000,000 miles and 1,800,000,000 miles
respectively from the Sun, and still they obey its control.
An attempt has been made to suggest the dimensions
of the Sun in an earlier page, where there is a diagram
to reinforce the illustration. Earth and Moon might be
placed inside the Sun, and the Moon would continue to
make its circuit round the Earth, its path approaching little
more than half-way to the Sun's limits. So when mention
is made of the corona surrounding the Sun and spreading
outwards a vast distance into space, and of the " red flames "
that are visible at the Sun's edge during eclipse, it is well to
keep in mind what are the real proportions of these appendages of the Sun.
Big as the Sun is, the corona which we shall see (clouds
permitting) on the 29th June is upon a scale still more
stupendous.
Withal, the Sun is not a heavy body. Mass for mass, the
Sun has only one-fourth the density of the Earth.
And two bodies more dissimilar it would be difficult to
imagine. We tread solid ground. Actually what state of
things exist within the Sun's vast globe we can speculate
upon, but do not really know, for nothing that can be repro48
49
G U I D E TO T H E ECLIPSE
duced on Earth is at all akin to them. The pressures must
be almost grotesque. We may occasionally see an oil well
or an artesian well sunk a few hundred feet into the ground
" spouting " a torrent high into the air. Imagine the forces
that can eject matter up from the Sun to heights measured
by hundreds of thousands of miles !
What is seen by the naked eye and the telescope as one
glances up at the Sun is an apparently steady surface; but
it is not steady like the solid ground of Earth. It is constantly being renewed. At times the Sun's surface breaks
out with dark spots which may be small when first detected
and will afterwards expand to enormous dimensions. The
Earth could be comfortably tucked away in one of the larger
spots. These frequent features of the Sun are also familiar
features, for on occasion a spot is so large that it is visible
to the naked eye through a smoked glass. Spots come and
disappear in a few weeks, often in a few days. A large spot
commonly breaks up into a number of small spots before
we see the last of it. The spots are the most obvious evidence
of activity at the Sun's surface.
Sunspots have been most laboriously studied, and certain
results obtained. The appearance of a spot is that of an
irregular black chasm, pitting the Sun's bright face, with
a rim about it that is less dark. They may be likened to
deep holes made in the Sun's face, and there is definite
evidence of motion in a vortex. Evidently they are violent
eruptions of some kind, indicating vast disturbances below
the Sun's visible surface. Their nature has not yet been
definitely decided. They may be due to an uprush of
heated matter from the Sun's interior (the darkness of the
" c h a s m " is only relative to the light surrounding it;
actually it is intensely bright). Alternatively, they may be
due to gases rushing downwards.
T H E " DAILY TELEGRAPH "
50
That the spots are of the nature of whirling storms,
analogous to terrestrial cyclones or tornadoes, was suggested
many years ago, but that view was not universally accepted.
In numbers of cases their appearance seemed definitely to
contradict the theory. It has, however, in the last few
years been confirmed in the following way. An ingenious
experiment based on what is known as the Zeeman effect
has shown the existence of a magnetic field around sunspots, which may be, and probably is, due to rapid rotation
of matter carrying electrons. From the study of this
magnetic field around sunspots some curious facts about the
direction of the rotation have emerged, but the matter is
too technical for discussion here.
But sunspots are not the only signs of activity at the Sun's
surface. In a telescope, with steady air and under suitable
magnification, the whole of the Sun's surface wears a mottled
or granulated appearance. It is undergoing violent agitation ; for if two photographs are taken in the same instrument
in rapid succession, it is rarely possible for the mottlings
shown in one to be identified in the other. The form
changes continually.
The Sun does not rotate as a solid body. The spots
themselves undergo a drift, which varies according to the
solar latitude in which they occur, giving us the idea that at
the Sun's surface there is a motion something like that of a
whirlpool.
As spots and mottlings (and the Sun itself) are invisible
at total eclipse, it might be thought unnecessary to give
consideration to them. But they bring testimony of the
agitated state of the Sun, which it is of first importance
should be understood. That agitation also prevails in the
Sun's surroundings, and furthermore, sunspots are directly
related to the phenomena of eclipse.
51
G U I D E T O T H E ECLIPSE
Observations over many decades have shown that sunspots
wax and wane in number and size in a period whose mean
length is a little more than eleven years. The period may
differ from this length by a year or two on either side, but
the excess of spots, and their largeness, at some times and
their scarcity and smallness at others, are facts well established. If an eclipse of the Sun happens when spots are in
greatest number and extent upon the Sun's face, the corona
is of the uniformly distributed type, bunched up closely
about the Sun, like the rays shown on a compass card.
When, on the other hand, there are few sunspots, the corona
is then " winged " and extends out laterally, sometimes
with long streamers on either side, but with no profusion
about the regions of the Sun's poles. Here are seen to be
only a few wisps, known as " polar plumes." The maximum
of sunspots is due at the end of this year or in 1928. It is,
therefore, the uniformly distributed type of corona that is
likely to appear in June.
By the watcher of a total eclipse, the last thing seen as
the auspicious moment is about to arrive is the breaking up
of the exceedingly thin crescent of the Sun into " Baily's
Beads." As the last of them disappears the brilliant corona
bursts into sight. Totality has begun. But by those trained
to look for it, for a second or two before (and after) totality
a scarlet " chromosphere " is visible, fringing the circumference of the dark Moon, and from this exceeding thin
crescent of light spring up the towering prominences, or
"red flames," of varied but generally of a rosy hue. Together, these appearances give the startling suggestion
that far out in the heavens is a world on fire. The chromosphere is an envelope, or layer, of the Sun, consisting of very
bright gases, chiefly hydrogen. It has a depth of some
4.000 miles.
T H E " DAILY TELEGRAPH "
52
The " red flames," rising to great heights, do not as
suddenly disappear, and may generally be observed throughout the duration of total eclipse. They glow against the
illuminated background of the pure white corona, and have
on occasion been visible in the rapidly increasing darkness
just before total eclipse. If very large, they may be seen
by the naked eye.
In early days of scientific investigation neither corona nor
" red flames " were allowed to the Sun. The former was
thought to be created in our atmosphere, and to be a mere
optical effect due to the glare around the eclipsed sun. The
" red flames " were given to the Moon, and were taken to
indicate the existence of a lunar atmosphere.
Imagination ran riot in attempts to convey an impression
of these flame-like projections from the Sun's edge.
" Alpine mountains coloured by the rising or setting Sun,"
said one.
" A box of ebony (the Moon) garnished with rubies," was
another's description of the sight presented.
Airy, the Astronomer-Royal, likened these jagged, flaming
protuberances at the Moon's edge to the teeth of a circular
saw.
That the so-called flames are actual parts of the Sun was
settled in 1851. It was then noticed that the Moon passing
out from eclipse gradually covered over portions of them,
beginning at the base and advancing till they were entirely
obscured, while a few moments later other flames at the
opposite edge of the Moon were as gradually unfolded to
view. This was confirmed by photographs taken in 1860
—the first practical application of the camera to the solution
of the riddle of the heavens. Later the spectroscope, by
indicating the materials composing the " flames," drove out
any possible doubts.
AN
ENORMOUS " FLAME " PROMINENCE.
It attains a height of 310,000 miles.
53
G U I D E T O T H E ECLIPSE
Since the eclipse of 1860, these features have been
commonly known as the Sun's prominences, or protuberances, and it will be in keeping with modern practice
to employ those terms.
The prominences are, as they appear to the eye to be,
parts of the Sun's matter driven upwards by violently
eruptive forces within. They ascend at terrific speeds, are
constantly in motion, attain great heights, and at the crest
sometimes appear to fold over or topple over. The forms
they take are of infinite variety. Professor Young has given
this description:
Their form and appearance change with great rapidity, so
that the motion can almost be seen with the eye. Sometimes
they consist of pointed rays, diverging in all directions, like
hedgehog spines. Sometimes they look like flames; sometimes
like sheaves of grain; sometimes like whirling waterspouts,
capped with a great cloud; occasionally they present more
exactly the appearance of jets of liquid fire, rising and falling
in graceful parabolas; frequently they carry on their edges
spirals like the volutes of an Ionic column; and continually
they detach filaments which rise to a great elevation, gradually
expanding and growing fainter as they ascend, until the eye
loses them. There is no end to the number of curious and
interesting appearances which they exhibit under varying
circumstances. The velocity of motion often exceeds one
hundred miles a second, and sometimes, though very rarely,
reaches two hundred miles a second.
It is now known that the uprush at times occurs at velocities
still higher than these.
Although of almost infinite variety, the forms may be
rudely classed in two groups—namely, (1) the vast cloud-like
arched prominences, linked to the Sun by stems, which may
spread over no small distance of the Sun's round edge ; and
(2) the smaller eruptive flame prominences, shaped like jets,
spikes, fountains, and waterspouts. It is the cloud-like
form which gives not only the biggest prominences, but
T H E " DAILY TELEGRAPH "
54
generally those that are longest lived. The spectroscope
has shown them to be immense masses of incandescent
gases, chiefly hydrogen and the vapours of calcium and
helium. Flame prominences, in addition, frequently disclose the injection from below of metallic elements, such as
iron, barium, and magnesium. The last are quite commonly associated with small sunspots.
In the past half-century the study of prominences has been
mostly accomplished by the method of using a spectroscope
with an open slit. The whole prominence is thereby made
visible, and its image can be kept in the field and its development watched. Janssen in France, and Sir Norman
Lockyer in England, discovered the method simultaneously
after the eclipse of 1868, and Sir William Huggins improved
upon it. The spectroscope is, in principle, merely a glass
prism, which spreads out a beam of composite light—as
sunlight is—passing through it into a long band of all the
colours. As a prominence most strongly discloses itself by
the light of a dominant coloured ray, rays of other colours
and refrangibility are dispersed out of the field of vision by
a train of prisms.
Later Professor Hale, of Chicago, and Deslandres, of
Paris, almost simultaneously invented an ingenious instrument named the spectro-heliograph, by which at any time
all the prominences rising up around the Sun's edge, and
the layer from which they rise, can be photographed on a
single plate with one exposure. By the same instrument
prominences are photographed all over the Sun's disc, and
not only at such times as they are brought by the Sun's
rotation to the edge.
Accordingly there is no longer dependence upon the rare
occurrence of eclipse, and observations of prominences have
become a matter of daily routine at certain observatories.
55
G U I D E TO T H E ECLIPSE
Chance brought a large horn-shaped prominence into view
at the total eclipse of the Sun in 1868. This appeared to
be the result of two issuing jets, which coalesced at a height
of about 16,000 miles above the Sun's surface, and thereafter
CHROMOSPHERE AND PROMINENCES.
Photographed by Hale without an eclipse.
rose in an ascending spiral to the great height of 100,000
miles. In 1886 a prominence, partly spiral, rose to a height
of 70,000 miles, where it had split up into three jets, two of
which fell over towards the Sun. The central jet thereafter
continued its uprush, till it reached a height of 150,000 miles.
These are, however, only big brothers amongst the
" little fellows." Cloud-like prominences frequently seen
are on a scale still more stupendous. One observed from
India in 1917, in breaking up rose to a height of over half
a million miles before it faded away from sight. Its speed
was measured, and the greatest velocity attained was found
T H E " DAILY TELEGRAPH '
56
to be 285 miles a second. A prominence not so large as this,
but still of vast magnitude, was the subject of an interesting
observation by Professor Young. It showed to the eye an
arched, cloud-like form 100,000 miles in length and 54,000
miles high. It seemed to float above the Sun's surface at
an elevation of some 15,000 miles, being connected with
the parent body by three or four wispy upright columns,
distinctly seen. This was its state at 12h. 30m., when the
observer was called away.
Returning twenty-five minutes later (says Professor Young),
I found that the whole thing had been literally blown to shreds
from beneath. In place of the quiet cloud I had left, the air,
if I may use the expression, was filled with flying debris—a
mass of detached, vertical, fusiform filaments, brighter and
closer together where the pillar had formerly stood, and rapidly
ascending. They rose, with a velocity estimated at 166 miles
a second, to fully 200,000 miles above the Sun's surface, then
gradually faded away like a dissolving cloud, and at 1.15 only
a few filmy wisps, with some brighter streamers low down,
remained to mark the place.
Young some years later saw the main features above
chronicled repeated on a still vaster scale; for the exploded
prominence then attained an altitude of 350,000 miles.
It has happened at several recent total eclipses that there
has been a very large prominence at the edge of the Sun.
The coincidence in time must be fortuitous, but in view of
the present stage of solar activity it is not unlikely that there
will be such a prominence visible on 29th June.
Opportunity occurred to witness the dramatic development of a prominence of enormous size that was a conspicuous object at the total eclipse of the Sun seen from
Brazil on 29th May, 1919 (see illustration). Its height was
135,000 miles, and it formed a luminous arch over many
degrees of the Sun's surface, supported intermediately by
57
G U I D E T O T H E ECLIPSE
columns of uprushing or descending vapours. First one
end of the arched structure was seen to break away, then the
other. Thereafter the whole structure commenced to rise
rapidly, though still retaining a link with the Sun by faint
wisps. For five and a half hours its progress in height was
watched, and in that brief time it rose from 135,000 miles to
attain a height of 470,000 miles above the surface, a distance
exceeding half the diameter of the Sun. Its complete breakup was observed a few hours later.
Sir Norman Lockyer saw a prominence 40,000 miles high
shattered to pieces in ten minutes.
A yet more startling experience came to Trouvelot at the
Harvard College Observatory, where he witnessed a gigantic
comma-shaped prominence 82,000 miles high vanish before
his eyes by a withdrawal of light as sudden as the passage
of a flash of lightning.
From the brief life history of these larger prominences,
impelled outwards by enormous forces of eruption in this
manner, we gain a means of accounting for the vast diffusion
of matter in the neighbourhood of the Sun. The material
of the prominences so violently ejected is not seen to fall
back into the Sun. So far as our sight is concerned, it just
disappears; it fades away in that region immediately about
the Sun wherein we know, from its appearance at total
eclipse, the corona is situated. There is a certain speed of
ejection—it has been computed at 379 miles a second at the
Sun's surface—above which matter thrown out will, if it
encounters no resistance, escape for ever from the Sun's
control to bring it back.
The eclipse photographs of the corona generally show
some distinctive features, such as arches or rings or increased
brightness, near prominence matter. And that brings us to
the glorious corona.
T H E " DAILY TELEGRAPH '
58
Unfortunately, the corona still eludes all attempts either
to photograph it or to observe it visually by telescope or
spectroscope save at the rare occurrences and in the brief
moments of total eclipse of the Sun. Its spectacular appearance has been described in earlier pages, and the structure—
what little is known of it—may now be dealt with in more
detail. It is brightest nearest to the Sun, and the light
rapidly diminishes as distance increases. This brightest area,
the " inner corona " as it is termed, is best studied when the
corona is far extended, at periods of sunspot minima. It is
then distinguished by filaments or short tufts of light, which
are particularly noticeable at the poles. These may end in
points, like leaves, or fade from sight before a point is
reached, leaving the end square.
Like appearances may occur at all parts of the Sun's
edge, but as the widest extension of the corona is at the
equatorial regions, the paths in which the streamers lie, the
tufts are apt to be merged and lost in the greater radiance
from those areas.
The filaments or tufts not uncommonly interlace. In
places parts of the corona seem to be separated by dark
rifts. It is as though we see through them the sky beyond.
An unexpected and baffling discovery made at an eclipse in
1871 was that the matter which gives the brightest and most
characteristic line in the spectrum of the corona is also
present in these dark rifts.
Varying in dimensions and form as seen at different
eclipses, the corona commonly extends as a conspicuous
aureole of bright light around the Sun to a distance of about
one-half of the Sun's diameter. Wings, or streamers, will
on occasion reach out on both sides to twice the Sun's
diameter. A very striking appearance of the far-flung
streamers was recorded at the eclipse of the 29th July, 1878,
59
G U I D E T O T H E ECLIPSE
but it must be admitted that the observation on that occasion
was made under quite exceptional conditions. Professor
Langley, whose task was to draw the corona, watched this
eclipse from the summit of Pike's Peak, one of the loftiest
mountains of Colorado, at a height of 14,000 feet. The air
at that altitude was exceedingly rare and clear. He reported :
During totality the Sun was surrounded by a narrow ring—
hardly more than a line—of vivid light, presenting no structure
to the naked eye (but a remarkable one in the telescope); and
this faded with great suddenness into a circular nebulous
luminosity between two and three diameters of the Sun wide.
The most extraordinary thing, however, was a beam of light,
inclined at an angle of about 45 degrees, about as wide as the
Sun, and extending to the distance of nearly six of its diameters
on one side and over twelve on the other; on one side alone,
that is, to the amazing distance of over ten million miles from
its body. The direction, when more carefully measured, it
was interesting to note coincided closely with that of the
Zodiacal Light, and a faint central rib added to its resemblance
to that body.
With the telescope, the whole of the bright inner light close
to the Sun was found to be made up of filaments bristling in
all directions from the edge; not concealing each other, as we
might expect such things to do upon a sphere, but fringing the
Sun's edge in definite outline.
On the occasion of the eclipse of January, 1898, the
corona's rays were photographed and traced to a length of
six or perhaps more of the Sun's diameters.
Beautiful photographs of the corona are now taken, but
for its study entire a number of prints at different time
exposures are necessary, and pictorially it is best represented
in a composite photograph. A second or two may be
enough to get a picture of the brightest (innermost) parts
impressed upon modern highly sensitive plates, but a long
exposure is necessary to pick up the faint extremities of the
streamers, which are very little brighter than the sky.
T H E " DAILY TELEGRAPH "
60
61
G U I D E T O T H E ECLIPSE
The matter out of which the corona is formed is still
mysterious. In the spectroscope the prism breaks up its
light into a colour band which consists of bright lines
imposed upon a faint continuous background, and the most
conspicuous of these bright lines is given by a green ray.
It proceeds from every part of the corona, whether near the
Sun or in the streamers distant from it. No known element
on Earth gives the same lines. Till some solution arrives,
this unknown, hypothetical element found in the corona
has been named coronium.
Another element in the corona that awaits identification
gives a bright line in the red end of the spectrum, that has
been occasionally but is not always seen.
Incandescent solid or liquid particles and gaseous emissions
constitute the source of part of the light of the corona, but
it has been determined that much of it is reflected sunlight.
In this halo around the Sun there must be an infinity of
minute moving particles. Various estimates have been made
of the amount of light that the brilliant corona sheds, and it
appears to be about one-half of that of the full Moon. There
is evidence obtained at various eclipses that the intensity of
the light varies.
Little is known about the corona, and of that little much
is merely negative. It is an actual material appendage of
the Sun. It is not an atmosphere of the Sun weighing freely
upon its surface. We know from our own experience that
the atmosphere is densest at sea-level, and becomes rarer
and rarer as we ascend a mountain-side. The trouble in
climbing Mount Everest is not that the ascent is too steep,
but that as the summit is approached the atmosphere is too
rare for explorers to breathe. The vertical ascent is only
about five miles. The corona shows no increase of density
downwards, though it is piled up to a depth of hundreds of
T H E " DAILY TELEGRAPH "
62
thousands of miles, and at the Sun's surface gravitation is
many times greater than at the Earth's surface.
Vast as it is, the corona has no solidity as we understand
the term—that is to say, it has less substance than the most
elusive mist in our atmosphere. It probably contains much
less matter, volume for volume, than the highly exhausted
tubes with which the modern physicist works. Comets are
themselves objects of almost inconceivable tenuity. Yet a
comet will pass through the corona unchecked and unharmed.
We are at a loss to explain it, though it may be that electrical
forces working in high vacua have something to do with
the production of the strange and varied forms revealed at
eclipses.
The motion of the corona still awaits investigation, for
the brief moments of totality give small opportunity for
observing any changes. Plans were laid at the long eclipse
at Sumatra (6½ minutes) to pursue inquiry into this matter,
but clouds interrupted. Long ago excited observers of
total eclipse made report that the whole structure of the
corona was turning round the dark globe of the Moon,
like a firework Catherine-wheel, but that unquestionably
was mere imagination.
We cannot place any bounds to the corona, or assign to it
definite shape. All that can be said is that its extremities
fade from our sight into the surrounding sky. As it is a
part of the Sun, manifestly the Sun is a much larger body
than when seen in the day lit sky it seems to be. A suggestion has been made that the exceedingly tenuous rays of the
corona may even reach out to Earth, and that what we call
the Sun is merely the bright central mass of a vast nebula.
Little, however, is to be gained by such speculations.
At an eclipse of 1882, observed in Egypt, there appeared on
the photographic plates the image of a bright comet very
63
G U I D E TO T H E ECLIPSE
near the Sun, with graceful curving tail. It was also visible
to the eye in the moments of darkness, but never has it been
seen since. A faint comet was found on the plates of the
Lick Observatory expedition to Chili eleven years later.
Many observations have been made at eclipses with the
hope of finding planets moving nearer to the Sun than
Mercury, but always without success. The mythical planet
Vulcan has also eluded the most painstaking search undertaken at these favourable times.
NOTE
MAKING A SHADED GLASS
Already e m p h a s i s has b e e n laid u p o n t h e necessity for those w h o
go o u t to observe t h e T o t a l Eclipse of t h e S u n providing t h e m selves with a s h a d e d glass of s o m e kind for w a t c h i n g t h e phases
before totality. A smoked glass is d i r t y to h a n d l e , its density is
a p t to be irregular, a n d t h e smoking is always liable to be r u b b e d
off by contact w i t h t h e cover or t h e fingers.
It is b e t t e r to use a developed p h o t o g r a p h i c negative on glass.
Best of all, however, is t h e p r e p a r a t i o n of a negative for t h e
express p u r p o s e , and this is a m o s t simple m a t t e r . Place an
u n e x p o s e d negative in its carrier in t h e d a r k r o o m . T h e n take t h e
closed carrier o u t into a good light, a n d w i t h d r a w t h e s h u t t e r
slowly. W h e n it is o u t to its full extent, close t h e s h u t t e r rapidly,
with a s n a p . Afterwards develop t h e plate, and it will be f o u n d
t h a t t h e density is nicely graded from t h e deepest to t h e lightest
part.
A single negative so treated will give all t h a t is r e q u i r e d . T h e
q u a r t e r - p l a t e will d o , b u t a half-plate can be used w i t h m o r e
comfort.
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