Astronomy of To-day

d another, and thus intercept its light for a while. The moon, being the nearest object in the universe, will, of course, during its motion across the sky, temporarily blot out every one of

of the sun is almost of the same apparent size as that of the moon, and so the complete hiding of the sun can last but a few minutes at the most; whereas

ly the same manner as the moon does, but we cannot see

not able to note them in the act of passing over stars and so blotting them out; but such

eing in fact the exact reverse of an occultation. As there is no appreciable body nearer to us than the moon, we can never see anything in transit across her disc. But since the planets Venus a

they will often pass behind or across his disc. Such occultations

atively short, and reaches out in space for only about a million miles. There is no visible object except the moon, which circulates within that distance from our globe, and therefore she is the only body which can pass into this shadow. Whenever such a thing happens, her surface at once becomes dark, for the reason that she never emits any light of her own, but merely reflects that of the sun. As the moon is continually revolving around the earth, one would be inclined to imagine that once in every month, namely at what is called full moon, when she is on the other side of the earth with respect to the sun, she ought to pass through the shadow in questi

on than an eclipse of the sun. As Mr. J.E. Gore[4] puts it: "The darkening of the sun's light by the inte

ey exhibit, however, one of the most remarkable evidences of the globular shape of our earth

n two positions; i.e. entirely plunged in the earth's shadow and therefo

intense as one would expect, when one considers that the sunlight at that time should be wholly cut off from it. The occasions indeed upon which the moon has completely disappeared from view during the progress of a total lunar eclipse are very rare. On the majority of these occasions she has appeared of a coppery-red colour, while sometimes she has assumed an ashen hue. The explanations of these variations of colour is to be found in the then state of the atmosphere which surrounds our earth. When those portions of our earth's atmosphere th

is a very much smaller body than the sun, and also very much the nearer to us of the two, it will readily be understood that the portion of the earth from which the sun is seen thus totally eclipsed will be of small extent. In places not very distant from this region, the moon will appear so much shifted in the sky that the sun will be seen only partially eclipsed. The moon being in constant movement round the earth, the portion of the earth's surface from which an e

seen as total, will lie outside the surface of the earth. Such an eclipse is thus not dignified with the name of total eclipse, but is

Eclipse o

al Eclipse

s entirely blotted out by the Moon. From B it is seen partially blotted out, because the Moon is t

Eclipse of the Sun, the position A l

that the earth is, at times, a little nearer to him than at others. The sun will therefore appear to us to vary a little in size, looking sometimes slightly larger than at other times. It is so, too, with the moon, at the focus of whose orbit the earth is situated. She therefore also appears to us at times to vary slightly in size. The result is that when the sun is eclipsed by the moon, and the moon at the time appears the larger of the two, she is able to blot out the sun completely, and so we can get a total e

on at all. On the other hand, the greatest number of eclipses which can ever take place during a year are seven; that is to say, either five solar eclipses and two lunar, or

h makes a total solar eclipse just possible. The sun is about 400 times farther off from us than the moon, and enormously greater than her in bulk. Yet the two are relatively so distanced from us as to look about the same size. The result of this is that the moon, as has been seen

three-quarters of his disc are covered. Then a wan, unearthly appearance begins to pervade all things, the temperature falls noticeably, and nature seems to halt in expectation of the coming of something unusual. The decreasing portion of sun becomes more and more narrow, until at length it is reduced to a crescent-shaped strip of exceeding fineness. Strange, ill-defined, flickering shadows (known as "Shadow Bands"

dots, known as "Baily's Beads." The reason of this phenomenon is perhaps not entirely agreed upon, but the majority of astronomers incline to the opinion that the so-called "beads" are merely the last remnants of sunlight peeping between those lunar mountai

otal E

nnular

"Baily's

other than the celebrated phenomenon widely known as the Solar Corona. It was once upon a time thought to belong to the moon, and to be perhaps a lunar atmosphere illuminated by the sunlight shining through it from behind. But the suddenness with which the moon always blots out stars

the while in the darkened heaven. Meantime around the observer animal and plant life behave as at nightfall. Birds go to roost, bats fly out, worms come to the surface of the ground, flowers close up. In the Norwegian eclipse of 1896 fish we

corona on account of the blaze of sunlight, so are we likewise unable to see the chromosphere because of the dazzling white light which shines through from the body of the sun underneath and completely overpowers it. When, however, during a solar eclipse, the lunar disc has entirely hidden the brilliant face o

n standing out like blood-red points around the black disc of the moon, and remain thus during a good part of the total phase. These projections are known as the Solar Prominences. In the same way as the

ths of time in different eclipses. It is usually of about two or three minutes

ht and heat returns once more to the earth, and nature recovers gradually from the gloom in which she has been plunged. Ab

ents of the sun which a total eclipse reveals to us. Our further consideration of them must,

"grandest and most awe-inspiring sights" which man can witness. Needless to say, such an occurrence used to cause great consternation in less civilised ages; and that it has n

in order that not a moment may be wasted when the longed-for totality arrives. Such preparation is very necessary; for the rarity and uncommon nature of a total eclipse of the sun, coupled with its exceeding short duration,

sition of the track of totality well-nigh impossible. Thus chance alone would have enabled one in those days to witness a total phase, and the probabilities, of course, were much against a second such experience in the span of a life-time. And even in more modern times, when the celestial motions had come to be better understood, the difficulties of foreign travel s

an eclipse with its actual occurrence. Similarly, by calculating backwards, astronomers have discovered the times and seasons at

t eclipses. The Chaldean astronomers had indeed noticed very early a curious circumstance, i.

me time next year. However, the nicely balanced behaviour of the solar system, an equilibrium resulting from ?ons of orbital ebb and flow, naturally tends to make the members which compose that family repeat their ancient combinations again and again; so that after definite lapses of time the same order of things will almost exactly rec

e exam

gust 30, 1905, was a repetiti

ry 23, 1906, corresponded to that w

y 10, 1907, was a recurren

me upon a total solar eclipse predicted for September 10, 1923, which will re

the sky, the early Chaldeans, had arrived at this remarkable generalisation; and they used it

interesting and fascinating by-paths in astronomy, t

ealt with. This limitation will, however, not affect the arguments in the slightest, and it will

exactly reproduced, the shadow-track does not pass across the earth in quite the same regions. It is shifted a little, so to speak; and each time the eclipse comes round it is found to be shifted a little farther. Every solar eclipse has therefore a definite "life" of its own upon the earth, lasting about 1150 years, or 64 saros returns, and working its way little by little across our globe from north to south, or from south to north, as the case may be. Let us take an imaginary example. A partial eclipse occurs, say, somewhere near the North Pole, the edge of the "partial" shadow just grazing the earth, and the "track of totality" being as yet cast into space. Here we have the beginning of a se

from north to south. We might have taken one moving fro

the world, they would lie one beneath another like a set of steps. This is, however, not the case, and the reason is easily found. It dep

make one-third of a rotation upon its axis before the eclipse takes place. Thus at every recurrence the track of totality finds itself placed one-third of the earth's circumference to the westward. Three of the recurrences will, of course, complete the circuit of the globe; and so the fourth recurrence

ss after some 12,000 years; so that, at the end of that great lapse of time, the entire "life" of every eclipse shou

ries of eclipses of the moon progressing from north to south. At each recurrence the partial phase will grow greater, its boundary encroaching more and more to the southward, until eventually the whole disc is enveloped by the shadow, and the eclipse becomes total. It will then repeat itself as total during a number of recurrences, until the entire breadth of the shadow has been passed through, and the northern edge of the moon at length springs out into sunlight. This illuminated portion will grow more and more extensive at each succeeding return, the edge of the shadow appearing to recede from it until it finally passes off at the sou

asons, to be much shorter than that of an eclipse of the sun

on the 24th of June 1797. Its next appearance was on the 6th of July 1815. It has not been possible to show the tracks of totality of these two early visitations on account of the distortion of the polar regions consequent on the fiction of Mercator's Projection. It is therefore made to commence with the track of its third appearance, viz. on July 17, 1833. In consequence of those variations in the apparent sizes of the sun and moon, which result, as we have seen, from the vari

wing a portion of the progress of the Total Solar Ecli

l Essays (p. 40

ter number of days than ten; but this is easily explained when allowance is made for intervening leap