THE SHINING MOON
'Once upon a time,' long, long ago, the earth was not a compact, round,
hard body such as she is now, but much larger and softer, and as she
rotated a fragment broke off from her; it did not go right away from
her, but still went on circling round with the motion it had inherited
from her. As the ages passed on both the earth and this fragment, which
had been very hot, cooled down, and in cooling became smaller, so that
the distance between them was greater than it had been before they
shrank. And there were other causes also that tended to thrust the two
further from each other. Yet, compared with the other heavenly bodies,
they are still near, and by looking up into the sky at night you can
generally see this mighty fragment, which is a quarter the diameter of
the earth--that is to say, a quarter the width of the earth measured
from side to side through the middle. It is--as, of course, you have
guessed--the moon. The moon is the nearest body to us in all space, and
so vast is the distance that separates us from the stars that we speak
as if she were not very far off, yet compared with the size of the earth
the space lying between us and her is very great. If you went right
round the world at the thickest part--that is to say, in the region of
the Equator--and when you arrived at your starting-point went off once
again, and so on until you had been round ten times, you would only then
have travelled about as far as from the earth to the moon!
The earth is not the only planet which has a moon, or as it is called, a
satellite, in attendance. Some of the larger planets have several, but
there is not one to compare with our moon. Which would you prefer if you
had the choice, three or four small moons, some of them not much larger
than a very big bright star, or an interesting large body like our own
moon? I know which I should say.
'You say that the moon broke off from the earth, so perhaps there may be
some people living on her,' I hear someone exclaim.
If there is one thing we have found out certainly about the moon, it is
that no life, as we know it, could exist there, for there is neither air
nor water. Whether she ever had any air or water, and if so, why they
disappeared, are questions we cannot answer. We only know that now she
is a dead world. Bright and beautiful as she is, shedding on us a pale,
pure light, in vivid contrast with the fiery yellow rays of the sun, yet
she is dead and lifeless and still. We can examine her surface with the
telescope, and see it all very plainly. Even with a large opera-glass
those markings which, to the naked eye, seem to be like a queer
distorted face are changed, and show up as the shadows of great
mountains. We can only see one side of the moon, because as I have said,
she keeps always the same face turned to the earth; but as she sways
slightly in her orbit, we catch a glimpse of sometimes a little more on
one side and sometimes a little more on the other, and so we can judge
that the unseen part is very much the same as that turned toward us.
At first it is difficult to realize what it means to have no air.
Besides supporting life in every breath that is drawn by living
creatures, the air does numerous other kind offices for us--for
instance, it carries sound. Supposing the most terrific volcano exploded
in an airless world, it could not be heard. The air serves as a screen
by day to keep off the burning heat of the sun's rays, and as a blanket
by night to keep in the heat and not let it escape too quickly. If there
were no air there could be no water, for all water would evaporate and
vanish at once. Imagine the world deprived of air; then the sun's rays
would fall with such fierceness that even the strongest tropical sun we
know would be as nothing in comparison with it, and every green thing
would shrivel up and die; this scorching sun would shine out of a black
sky in which the stars would all be visible in the daytime, not hidden
by the soft blue veil of air, as they are now. At night the instant the
sun disappeared below the horizon black darkness would set in, for our
lingering twilight is due to the reflection of the sun in the upper
layers of air, and a bitterness of deathly cold would fall upon the
earth--cold fiercer than that of the Arctic regions--and everything
would be frozen solid. It would need but a short time to reduce the
earth to the condition of the moon, where there is nothing to shrivel
up, nothing to freeze. Her surface is made up of barren, arid rocks, and
her scenery consists of icy black shadows and scorching white plains.
[Illustration: _Paris Observatory._
THE MOON.]
The black shadows define the mountains, and tremendous mountains they
are. Most of them have craters. A crater is like a cup, and generally
has a little peak in the middle of it. This is the summit of a volcano,
and when the volcano has burst up and vomited out floods of lava and
debris, this has fallen down in a ring a little distance away from it,
leaving a clear space next to the peak, so that, as the mountain ceases
vomiting and the lava cools down, the ring hardens and forms a circular
ridge. The craters on the moon are immense, not only in proportion to
her size, but immense even according to our ideas on the earth. One of
the largest craters in our own world is in Japan, and this measures
seven miles across, while in the moon craters of fifty, sixty, and even
a hundred miles are by no means uncommon, though there are also hundreds
and thousands of smaller ones. We can see the surface of the moon very
plainly with the magnificent telescopes that have now been made, and
with the best of these anything the size of a large town would be
plainly visible. Needless to say, no town ever has been or ever will be
seen upon the moon!
All these mountains and craters show that at one time the moon must have
been convulsed with terrific disturbances, far worse than anything that
we have any knowledge of on our earth; but this must have been ages
ago, while the moon still probably had an atmosphere of its own. Now it
has long been quiet. Nothing changes there; even the forces that are
always at work on the earth--namely, damp and mould and water--altering
the surface and breaking up the rocks, do not act there, where there is
no moisture of any sort. So far as we can see, the purpose of the moon
is to be the servant of the earth, to give her light by night and to
raise the tides. Beautiful light it is, soft and mysterious--light that
children do not often have a chance of seeing, for they are generally in
bed before the moon rises when she is at the full.
We know that the moon has no heat of her own--she parted with all that
long ago; she cannot give us glowing light from brilliant flames, as the
sun does; she shines only by the reflection of the sun on her surface,
and this is the reason why she appears to change her shape so
constantly. She does not really change; the whole round moon is always
there, only part of it is in shadow. Sometimes you can see the dark part
as well as the bright. When there is a crescent moon it looks as if it
were encircling the rest; some people call it, 'seeing the old moon in
the new moon's arms.' I don't know if you would guess why it is we can
see the dark part then, or how it is lighted up. It is by reason of our
own shining, for we give light to the moon, as she does to us. The sun's
rays strike on the earth, and are reflected on to the moon, so that the
moon is lighted by earthshine as we are lighted by moonshine, and it is
these reflected earth-rays that light up the dark part of the moon and
enable us to see it. What a journey these rays have had! They travel
from the sun to the earth, and the earth to the moon, and then back to
the earth again! From the moon the earth must appear a much bigger and
more glorious spectacle than she does to us--four times wider across and
probably brighter--for the sun's light strikes often on our clouds,
which shine more brilliantly than her surface.
Once again we must use an illustration to explain the subject. Set a
lamp in the middle of a dark room, and let that be the sun, then take a
small ball to represent the earth and a smaller one for the moon. Place
the moon-ball between the lamp and the earth-ball. You will see that the
side turned to the earth-ball is dark, but if you move the moon to one
side of the earth, then from the earth half of it appears light and half
dark; if you put it right away from the lamp, on the outer side of the
earth, it is all gloriously lit up, unless it happens to be exactly
behind the earth, when the earth's shadow will darken it. This is the
full explanation of all the changes of the moon.
[Illustration: AN ECLIPSE OF THE MOON.]
Does it ever fall within the earth's shadow? Yes, it does; for as it
passes round the earth it is not always at the same level, but sometimes
a little higher and sometimes a little lower, and when it chances to
pass exactly behind it enters the shadow and disappears. That is what we
call an eclipse of the moon. It is nothing more than the earth's shadow
thrown on to the moon, and as the shadow is round that is one of the
proofs that the earth is round too. But there is another kind of
eclipse--the eclipse of the sun; and this is caused by the moon herself.
For when she is nearest to the sun, at new moon--that is to say, when
her dark side is toward us, and she happens to get exactly between us
and the sun--she shuts out the face of the sun from us; for though she
is tiny compared with him, she is so much nearer to us that she appears
almost the same size, and can blot him right out. Thus the eclipses of
both sun and moon are not difficult to understand: that of the moon can
only happen at full moon, when she is furthest from the sun, and it is
caused by the earth's shadow falling upon the moon; and that of the sun
at new moon, when she is nearest to him, and it is caused by the solid
body of the moon coming between us and the sun.
[Illustration: AN ECLIPSE OF THE SUN.]
Besides giving us light by night, the moon serves other important
purposes, and the most important of all is the raising of the tides.
Without the rising of the sea twice in every day and night our coasts
would become foul and unwholesome, for all the dead fish and rotting
stuff lying on the beach would poison the air. The sea tides scour our
coasts day by day with never-ceasing energy, and they send a great
breath of freshness up our large rivers to delight many people far
inland. The moon does most of this work, though she is a little helped
by the sun. The reason of this is that the moon is so near to the earth
that, though her pull is a comparatively small one, it is very strongly
felt. She cannot displace the actual surface to any great extent, as it
is so solid; but when it comes to the water she can and does displace
that, so that the water rises up in answer to her pull, and as the earth
turns round the raised-up water lags behind, reaching backward toward
the moon, and is drawn up on the beach, and makes high tide. But it is
stopped there, and meantime, by reason of the earth's movement, the moon
is left far behind, and pulls the water to itself further on, when the
first high tide relapses and falls down again. At length the moon gets
round to quite the opposite side of the earth to that where she began,
and there she makes a high tide too; but as she draws the water to
herself she draws also the solid earth beneath the water to her in some
degree, and so pulls it away from the place where the first high tide
occurred, leaving the water there deeper than before, and so causing a
secondary high tide.
[Illustration: THE MOON RAISING THE TIDES.]
The sun has some influence on the tides too, and when moon and sun are
in the same line, as at full and new moon, then the tides are highest,
and are called spring tides; but when they pull in different directions,
as when it is half-moon, then the tides are lowest and are called neap
tides.