THE MOON, THE EARTH’S DAUGHTER
=How the Moon Was Made.=—There was a time away back in the beginning of
the planets when the Earth did not have a Moon.
Two ideas among others have been worked out to account for the birth
of the Moon and these are somewhat alike, for both agree that just as
the Earth was once a part of the Sun and was separated from the Sun and
became a planet so the Moon was once a part of the Earth and was thrown
off and became her daughter.
[Illustration: FIG. 101.—MOON AND EARTH JOINED TOGETHER LIKE A
DUMBBELL.]
The first idea as to how the Moon was made is that a smaller core was
formed in the gaseous matter of the Earth and that this core and the
core of the Earth, which were at first joined together like a dumbbell,
as shown in Fig. 101, began to spread apart like a pair of balls
fastened together with a piece of elastic when they are whirled rapidly
round each other, as shown in Fig. 102.
[Illustration: FIG. 102.—BALLS CONNECTED WITH AN ELASTIC.]
So, too, the high speed with which the Earth turned on its axis when it
was in the making caused the smaller part to slowly move away and it
became the Moon.
The second idea is like the first, except that the Earth is thought to
have cooled down until it was a melted mass, and it was then that a
great upheaval took place in which a part, one-eightieth as large as
that of the world itself, was torn out of its side and, whirling away
by centrifugal force, the Moon was born.
To throw off such a mighty part of its bulk as the Moon, it has been
figured out that the Earth must have made a complete turn on its axis
every 2 hours, instead of one turn in 24 hours, as it now does; and it
was while the Earth was turning at this terrific rate of speed that the
centrifugal force overcame the force of gravitation and tore the Moon
from the Earth’s side and formed a little world of its own.
[Illustration: FIG. 103.—MAP SHOWING PACIFIC OCEAN.]
It is believed by some astronomers that the Moon was once that part of
the Earth which is now filled up by the waters of the Pacific Ocean and
there are several reasons why this seems very likely.
First, if the waters which form the Pacific Ocean were rolled into a
big ball it would be just about the size of the Moon; second, the space
between the coasts of North and South America on the east, and Asia
and Australia on the west, will be seen by referring to Fig. 103 to be
roughly circular in form; third, there is a marked likeness between the
volcanoes in California, in the Hawaiian Islands and in Japan to those
on the Moon.
[Illustration: FIG. 104.—IMITATING THE VOLCANOES IN THE MOON.]
It was, doubtless, at this long ago time that the great volcanoes of
the Moon, as well as those of the coasts of and on the islands in the
Pacific Ocean were made, but what caused them can only be guessed
at. There are two ideas, also, to account for them; one is that the
pent-up gases inside the Earth and the Moon exploded and so threw up
the volcanoes; the other idea is that showers of gigantic melted masses
fell on the surface of both the Earth and Moon and so caused them.
An experiment to show how the volcanoes might have been formed by
showers of meteors can be made by covering the surface of your
starboard with a layer of soft clay about 4 inches thick, and then
throwing clay balls against it. Artificial volcanoes with craters and
all will result. Compare your artificial volcanoes with Fig. 105,
showing the real volcanoes on the Moon, and you will see they are quite
alike.
[Illustration: FIG. 105.—REAL VOLCANOES.]
The volcanoes of California, Japan and the Hawaiian Islands are, many
of them, still active, while those on the Moon have long since become
extinct. This is easily accounted for, since the mass of the Moon is
very small compared with that of the Earth, and hence, the Moon has
cooled off more quickly than the Earth. The result is that while the
Earth is yet hot and teeming with life and activity, the Moon is cold,
and dead and silent.
=Seeing the Moon With the Naked Eye.=—If you look at the full Moon with
the naked eye it will appear as a great, silvery-bright disk, and about
the same size as the Sun.
Look again and you will see that some parts of it are much brighter
than others, while another and closer observation will show you that
the light and shaded parts take on the expression of a man’s face, as
shown in Fig. 106. This is the famous _Man in the Moon_, and once you
make out the likeness you will never again be able to look the full
Moon in the face without seeing the man in it.
[Illustration: FIG. 106—NAKED EYE DRAWING OF FULL MOON.]
When we look at the Moon we always see the same side of it, which will
be readily understood when we come to the turning of the Moon on its
axis. As the Moon revolves about the Earth, you will see, if you look
toward the west at the right time of the month, just at dusk, a pale
_crescent_ of light, and very soon after the Sun sets it drops out of
sight below the horizon.
A few nights later the Moon will be seen, over in the sky toward the
east; its crescent shape grown into the first quarter, and the Moon
looks as if it was split in two. As the nights go by the Moon _waxes_
until it is _gibbous_ and finally the full Moon—with the man in
it—stands out round and clear and bright.
It is a good idea at this time, that is, when the Moon is full, to make
a drawing of her face, and the best time to do it is shortly after
twilight, for later in the evening the Moon is so bright it is hard to
see the details. After this the Moon begins to _wane_; it again becomes
gibbous; then reaches its last quarter later only a crescent can be
seen, and she finally disappears.
At times when the crescent is bright the whole dark disk of the Moon
can be seen glowing dimly with a reddish, copper color, and this is
called the _old Moon in the new Moon’s arms_. This copper-colored glow
is the _Earth-shine_ on the Moon, that is, the sunlight on the Earth,
which is reflected to the Moon and back again to us.
On one side of the Moon you may be able to see a dark oval spot which
is marked _Grimaldi_ on the maps of the Moon. Grimaldi is a great
plain, having nearly 14,000 square miles in it, with mountains flanking
it on the sides. This is another good eyesight test, for it takes a
mighty sharp eye to see it without a glass.
These and a dozen other interesting things on the Moon can be seen
without a telescope.
=The Motions of the Moon.=—The Moon turns round on its axis once every
month and it also revolves round the Earth once every month, so that
the Moon’s day and year are of the same length just like Mercury and
Venus, and this is the reason that one side of the Moon is always
turned toward the Earth, as you will see if you look at her through a
glass.
[Illustration: FIG. 107.—THE EXPERIMENT SHOWING HOW ONE REVOLUTION OF
THE MOON ROUND THE EARTH MAKES IT TURN ONCE ROUND ITS AXIS.]
A simple experiment will show the cause of this: Place an apple, which
we will call the Earth, on the bottom of an inverted glass on a table,
and draw a chalk circle a foot in diameter around it. Next, take a
tablespoon to represent the Moon, and hold it upright with the point of
its bowl on the chalk line and with the bowl turned toward the apple,
as shown in Fig. 107. Now, draw the spoon round the circle, turning it
in your fingers so that the bowl is always toward the apple.
It is easy to see that in order for the bowl of the spoon to be turned
toward the apple during all of its travels round the chalk circle the
spoon must also turn once round on its own axis, and this is the reason
we always see the same side of the Moon.
=The Moon’s Phases.=—Since one side of the Moon is always turned toward
the Earth, it is clear that this is the only side we can ever see, and,
further, we are only able to see as much of this side as is made bright
by the Sun’s light.
[Illustration: FIG. 108.—APPLE CUT TO SHOW CRESCENT.]
The different _aspects_ we get of the Moon as it revolves round the
Earth are called the _Moon’s phases_; and each phase has a name, as
the _new moon_; the _first quarter_; the _full moon_, and the _last
quarter_.
Between the new Moon and the first quarter, and between the last
quarter and the new Moon only a crescent, or sickle-like edge of the
Moon, can be seen; while between the full Moon and last quarter the
Moon is gibbous (pronounced gib´-us and meaning swelled, or shaped like
a football).
If you will look at the picture, Fig. 108, and the diagrams, Figs. 109
and 110, and do the experiment which follows, the way the phases of the
Moon are made will be perfectly clear.
The picture, Fig. 108, shows an apple from which a thin _sector_ or
slice has been cut. The lower picture shows the stem end of the apple
and from this point of view the part where the slice was cut out looks
wedge-shaped. This is the view of the Moon shown in Fig. 109, if we
could look down on it.
[Illustration: FIG. 109.—DIAGRAM SHOWING HOW THE MOON’S PHASES ARE
MADE.]
Now turn the apple on its side and the place where the slice was cut
out can be seen from the stem to the blossom end of the apple when it
takes on a crescent form. This is the view of the Moon we really get
between new Moon and its first quarter, as shown in Fig. 110.
The diagrams, Figs. 109 and 110, show the Earth in the center of the
Moon’s orbit and the Moon is pictured in eight positions, as it moves
round the Earth, one for each phase, while the sunlight falling upon
the Earth and the Moon is shown by streamers of light from the Sun
above.
The diagram, Fig. 110, shows how the sunlight falls on the Moon, but
you must always keep in mind that only that part of the Moon which is
in the sunlight and which is also inside of the line of its orbit can
be seen from the Earth.
[Illustration: FIG. 110.—DIAGRAM OF THE MOON’S PHASES AS WE SEE THEM.]
Starting now with the new Moon, Fig. 109, it will be seen that the
Moon is directly between the Earth and the Sun and hence that part of
the Moon toward the Earth is in the shadow. Now, since the eye can see
nothing in the sky which is not shining, and since the Moon rises and
sets at the same time as the Sun, we cannot see it. As the Moon moves
on round the Earth in the direction of the arrow and while half of it
is in the light and half of it is in the shadow as before, from our
position we are now able to see a narrow strip of its bright surface
which in Fig. 109 is shown as a wedge, but since we are looking at it
from an angle we see it as a crescent, as shown in Fig. 110.
The Moon having reached its first quarter sets at midnight and from the
Earth half of its bright surface can be seen, which of course is only
one quarter of the Moon’s whole surface. The next phase of the Moon is
when nearly all of its bright side can be seen. This is the gibbous
phase and the Moon then seems to be about the shape of a football.
After the gibbous phase the full moon appears and this takes place in
that part of the sky opposite the setting Sun. When the Moon is full it
shines all night and does not set until sunrise.
From this time on the bright part of the Moon which we can see grows
less and the gibbous phase again takes place. Soon the Moon reaches its
last quarter and gradually the straight rough edge is hollowed out and
another crescent is formed. The Moon is now in the east and the horns
of the crescent point to the west, just opposite to the direction the
horns of the new Moon pointed. The horns of the new and old crescents
always point away from the Sun and this also is a good thing to
remember.
To show how the Moon changes its phases perform the following simple
experiment: Peel half an orange and push a knitting needle through its
center and let this be the Moon. Your eyes will serve for the Earth and
a lighted lamp will make a very good Sun, all of which is shown in Fig.
111.
Hold the orange by the knitting needle well out from your body with the
peeled side toward you, and in such a position that the orange will be
between your eyes and the lamp. The side of the orange toward you will
be in the shadow and this represents the new Moon.
Now slowly turn your body round to the left and always hold the orange
with the peeled side toward you. You will see that the light from the
lamp striking the orange forms a crescent with its horns pointing away
from the light.
Keep on turning, a little at a time, and soon a quarter of the orange
will reflect the light and this is like the first quarter of the Moon.
When you have turned nearly halfway round nearly half of the orange
will shine by the reflected light of the lamp and you will have a fair
example of the gibbous Moon.
When you have turned your back to the light hold the orange above your
head so that your shadow will not hide it; now half of the orange—the
half that is peeled—reflects the lamp-light and represents the Moon
when it is full.
[Illustration: FIG. 111.—BOY, LAMP AND ORANGE SHOWING PHASES OF MOON.]
As you keep turning round the amount of light reflected by the orange,
which you can see grows less and less, the bright part at first being
gibbous, then the last quarter is seen, after that a thin crescent,
and finally when you have turned completely round the orange is again
between your eyes and the light, hence it can no longer be seen, and
the new Moon phase is again at hand.
=The Harvest and Hunter’s Moon.=—You will remember that on September
21 the days and nights are equal and this is called the _Autumn
Equinox_. The full moon that falls nearest to September 21 is called
the _Harvest Moon_ as it rises at nearly the same hour for several
nights in succession and this makes several long moonlight evenings in
succession. The _Hunter’s Moon_ follows the Harvest Moon.
=How the Moon Makes the Tides.=—When we are at the seashore we soon see
that there is a regular rise and fall of the ocean.
This rise and fall of the waters is called the _tide_, and if we note
the time when the waters have reached the highest point—which is called
_high tide_—we will find that a little over six hours later the waters
have reached their lowest point—or _low tide_.
Before the tide has reached the high point again another six hours and
some minutes have passed so that from one high tide to another high
tide 12 hours and 25 minutes have elapsed. These tides are chiefly
caused by two forces acting on the oceans, one being the attraction of
the Moon for the Earth, and the other being the centrifugal force set
up by the Earth’s motion round its axis.
The effect of the Moon’s attraction for the Earth is to pull the water
of the ocean on the side of the Earth nearest it, and this forms a
bulge, or great wave, while on the other side of the Earth the Moon’s
attraction is smaller for the water than it is for the solid Earth,
so the Earth is pulled away from the water. Thus two tidal waves are
formed at the same time, one on each side of the Earth, as shown in
Fig. 112.
[Illustration: FIG. 112.—ATTRACTION OF THE MOON CAUSES THE TIDES.]
Since the Earth revolves round its axis once in 24 hours these tidal
waves go round the Earth and as there are two tidal waves each day
there are two high tides and two low tides at every place on the ocean,
but these are chiefly noticeable on the coasts. Fig. 112 shows the
position of the Moon and the Earth, while the wavy lines around the
Earth represent the oceans.
=Spring Tides and Neap Tides.=—Not only does the Moon’s attraction
cause the tides, but the Sun’s pull on the Earth also produces tides.
When the Sun and Moon are in a line with the Earth they pull together
and the tides are raised very high and they fall very low, and these
high and low tides are called _spring tides_.
Since we have either new Moon or full Moon, when the Sun, Earth and
Moon are in a line, the spring tides occur at these times, or twice
every month. Figs. 113 and 114 show how the spring tides are formed.
[Illustration: FIG. 113.—HOW SPRING TIDES ARE FORMED.]
[Illustration: FIG. 114.—HOW SPRING TIDES ARE FORMED.]
When the Moon is at its first quarter, as in Fig. 115, or in its last
quarter, as in Fig. 116, the Sun’s pull and the Moon’s pull oppose each
other and the high tides are lowest. These low high tides, which take
place twice a month, are called _Neap tides_.
=A Trip to the Moon.=—Many stories have been told about imaginary
trips to the Moon and what the adventurers saw after reaching their
destination.
Our story is made up of facts and the only thing we shall imagine is
that we have made the trip and set foot somewhere on the Moon. Having
performed this mental somersault we shall carefully leave out all the
hard questions about living there without air and water, for this is a
pleasure trip and we don’t want to spoil the fun with details.
On landing after our 240,000-mile trip we find that there is not only
neither air nor water, but that the Moon is stone cold; even when the
Sun shines on it, it is freezing cold, while the temperature drops to
perhaps 300 degrees below zero when the Moon’s night comes on.
Our next observation will probably be that we feel much lighter than
we did on Earth and we are lighter in the very nature of things, for
the weight of bodies on the Moon is only one-sixth as much as they are
on the Earth. This is due to the Moon being so small and light that
gravity has only one-sixth as great an attractive force there as it has
on the Earth.
Supposing we still retained on the Moon as much strength as we had on
the Earth; then every time we took a step we would cover a distance
of 15 or 20 feet; if we jumped we would sail through space with the
agility of a Harlem goat, and if we played ball and batted the sphere
fairly it would shoot off a quarter of a mile and go twice as far from
the home plate.
[Illustration: FIG. 115.—HOW NEAP TIDES ARE FORMED.]
[Illustration: FIG. 116.—HOW NEAP TIDES ARE FORMED.]
Since there is no air on the Moon, in order to see one another the Sun
would have to shine directly on us, and if by any chance we should
get into a shadow we would be as completely lost to view as if we had
fallen into one of the craters, for a shadow on the Moon is as deep and
black as the darkest night you ever saw on Earth. Shadows as we know
them on the Earth are always softened, for the air scatters the light.
Nor would it do us any good to cry out or whistle, for, since sound
waves are carried by the air, and since there is no air on the Moon,
all our efforts to make ourselves heard would be useless, even if we
were only a few feet from each other. The Moon is just as silent and
cold and still as it looks, for, though it serves the Earth well as
a mirror to reflect the Sun’s light, it is, after all, only a great,
burned-out cinder.
Looking at the sky at night from the Moon, we are surprised to find how
much bigger and brighter the stars seem, and how many more of them can
be seen, than from the Earth. Here we see as many with the naked eye as
we could see from the Earth with a three-inch telescope.
The Earth itself is seen like a mighty Moon—a Moon as bright as 40 of
the Moons we are calling on, and so large is it that we can see, not
only the continents and oceans, but the polar ice caps and the plains
and the mountains as well, as we see objects of same size on Moon, as
shown in Fig. 117.
[Illustration: FIG. 117.—VIEW OF THE EARTH FROM THE MOON.]
Watching the Earth from this new viewpoint, we see it turn on its axis
every 24 hours and going through all the phases—crescent, quarter,
gibbous and full, and back to crescent again, just as the Moon does
when we see it from the Earth.
More curious than the Earth is the view we get of the Sun from the
Moon, the lack of air making the seeing so good that the spots on the
Sun, the fiery prominences and the thin corona can all be easily seen
with the naked eye.
When the Moon is new the whole half of the Earth that is turned toward
the Moon is sunlit and by its reflected light we can easily read our
time-card—for we must get back to Earth again and either write a book
or lecture about the wonders we have seen.
=The Moon and the Weather.=—We have seen in Chapter III that our
weather is entirely dependent on the Sun. Still it is believed by many
persons today that the Moon has also something to do with the changes
in the weather, just as it is the cause of the tides.
[Illustration: FIG. 118.—TELLING TIME BY THE MOON.]
Hence there have been handed down to us a large number of old sayings
to show what the weather will be during certain phases of the Moon. But
it has been proved by records kept of the weather that the Moon has
nothing whatever to do with it. For this reason no reliance is to be
placed in any forecast of the weather which is founded on changes of
the Moon.
=How to Tell Time by the Moon.=—After having learned how to tell the
hour of the day by the Sun you should learn to tell the hour of the
night by the Moon.
On some nights this is a very simple thing to do, for when the Moon is
full it is due south at exactly 12 o’clock midnight, as shown in Fig.
118.
Every night before the Moon is full you will find it due south 55
minutes earlier, so that you must subtract 55 minutes from 12 o’clock
for each day; that is, one day before full Moon it is due south at
11:05 P. M.; two days before full Moon it is due south at 10:10 P. M.;
three days before full Moon it is due south at 9:15 P. M., and so on.
After the Moon is full it will be due south 55 minutes later every
night and then you must add 55 minutes to 12 o’clock; that is, one day
after full Moon it is due south at 12:55 A. M.; two days after full
Moon it is due south at 1:50 A. M.; three days after full Moon it is
due south at 2:45 A. M., and so on.
The Moon’s day is 27½ of our days long.
The Moon’s year is 27½ of our days long.
The Moon’s diameter is 2,160 miles.
The distance from the Moon to the Earth is 240,000 miles.