CHAPTER XII.. What Is Meant by an Eclipse.

WHAT IS MEANT BY AN ECLIPSE.

Before telling you more about the other worlds in the Sun’s kingdom I should like you to understand what is meant by an Eclipse.

The word “Eclipse” really means “a failure”--as when something fails to shine because its light is somehow hidden or shadowed.

First, we will think about an ECLIPSE OF THE SUN.

For this we will forget all other worlds, and fix our minds only on the Earth, the Moon, and the Sun.

The Sun is in the centre, or, as a child would say, “in the middle.” The Earth journeys round him. The Moon also journeys round the Sun; and, as she goes, she curves backwards and forwards, so as to be on each side of the Earth in turn.

Sometimes she is outside the Earth, away from the Sun; and then we see her as Full Moon. Sometimes she is between the Earth and the Sun--only a little higher or lower, and not exactly between:--and then she is New Moon, with her bright face turned from us, so that we cannot see her.

Suppose the Moon, instead of being at “New Moon” a little higher or lower, were to pass just exactly between the Sun and us; what would happen?

We should see her as a dark round body, creeping over the face of the Sun, and hiding him from us.

And this is precisely what we do see, from time to time. Once in a while the Moon does come into the line between; and then we have an Eclipse of the Sun: we see the moon’s dark body covering or partly covering his face.

You must not think that the Moon is at such times any darker than usual. She always has a dark side and a bright side. At New Moon the dark side is towards us, and so we cannot see it at all--unless she happens to be just between the Sun and us.

But you must not suppose for a moment that she really touches the face of the Sun. The Moon is no nearer to the Sun than usual. She is only between him and us.

If you are in a room with a lamp on the table, and somebody holds a big ball just between your eyes and the lamp, what happens?

The lamp is eclipsed. It does not leave off shining, but to you it is eclipsed, or hidden. You see the dark ball, not the bright globe of the lamp beyond it.

That is how we have an eclipse of the Sun. Now and then, at New Moon, our Moon glides exactly between, just as the ball came between your eyes and the lamp. And then the light of the Sun is cut off from part of the Earth.

An eclipse of the Sun is always known about beforehand. The Moon’s pathway and the Earth’s pathway are so well understood by astronomers that they can tell when she will pass a little higher, or a little lower, and when she will go just between, so as to eclipse the Sun.

Then, when the moment comes, we look earnestly at the Sun, perhaps with telescopes, perhaps only with pieces of smoked glass to protect our eyes; and we see--

A dark round body touching the bright side of the Sun, then slowly crossing his face and blotting out his radiance.

Not that the Sun is dimmed, or that for a moment he leaves off shining. Other worlds see him still, as brilliant as ever. But to us, for a short space, his light is hidden by the solid Moon floating between.

For a few seconds, and no more, we have almost darkness. Then, on the side of the Sun where the moon seemed first to touch him, a line of light is seen. This widens fast, as the dark round moon draws away to the opposite edge and then vanishes, and the whole Sun shines out as usual.

Even when an eclipse can be seen it is often only a Partial eclipse, not Total. Only part of the Sun is hidden, not all of him. The Moon creeps over one edge, or perhaps over half of the Sun’s face, but she does not cover him quite.

Now and then we have what is called an Annular eclipse. The round dark body of the Moon is seen upon the face of the Sun, and a bright rim of the Sun is all round the Moon.

It seems odd that at one time the Moon should quite hide the Sun, and that at another time the Moon should be too small to hide him.

The reason is that the Moon is sometimes a little nearer to us, sometimes a little farther away; and the Sun too is the same--sometimes a little nearer, sometimes a little farther.

If an eclipse happens just when the Moon is at her farthest from us, and so seems her smallest, while the Sun is at his nearest to us, and so seems his biggest, then she is not large enough to cover his whole face. But if the Sun is at his farthest, and the Moon at her nearest, she can hide him entirely.

When a Total Eclipse is foretold, astronomers are eager to make the most of it. Telescopes are pointed at him, and photographs are taken. Much can be seen during a total eclipse which is hidden from us at other times, because the dazzling brilliance of the Sun’s body is for a few seconds cut off from our eyes.

The ocean of fire round the Sun is seen at his edge, outside the dark body of the Moon, by those who look through telescopes; also the sharp mountains of fiery gases, and the soft broad crown of light spreading away on all sides.

But the very utmost has to be made of each moment. Hardly has the Moon’s body covered the whole face of the Sun before she begins to move away from the side which first she seemed to touch; and as a bright line of light appears there, these wonderful sights vanish.

Remember, an Eclipse of the Sun never happens except at the time of New Moon. It is only then that the Moon can possibly be just between the Sun and our Earth.

Another kind of Eclipse, however, may happen at Full Moon; and that is an eclipse of the Moon herself.

An ECLIPSE OF THE MOON is partly like and partly unlike an Eclipse of the Sun.

In an Eclipse of the Sun we have the solid body of the Moon gliding in between, and hiding his light from us though all the time the Sun shines on just the same, behind the Moon.

Eclipse of the Moon. January 28, 1888.

In an eclipse of the Moon we, on the Earth, have no solid body between us and the Moon. Her brightness is not simply hidden, it is for the moment quenched by a shadow. For the shadow of our Earth falls upon her.

The Moon is bright only when the sunshine makes her bright. When the solid body of the Earth, gliding in between, cuts off the sunlight from her, then the Moon shines no longer. So long as she is plunged in the Earth’s shadow she is all dark.

You have seen with a lamp and a big ball how the Sun can be eclipsed by the Moon.

Now, instead of letting some one hold the ball between your head and the lamp, you must get some one to hold the ball farther off while you move with your head between the lamp and the ball. Place your head exactly between, so that its shadow covers the ball.

Then you have a picture of a Moon-Eclipse.

So once in a while, when the Earth goes exactly between Sun and Moon, the Moon for a very short time is not a bright world at all. She is quite a dull one. But the very moment she catches a glimpse of the Sun’s radiant face she begins to shine again.

There is, you see, a great likeness, as well as some difference, between an Eclipse of the Sun and an Eclipse of the Moon.

In an Eclipse of the Moon the Earth glides between Sun and Moon, and the Moon passes into the Earth’s shadow. In an Eclipse of the Sun, the Moon glides between Sun and Earth, and a part of our Earth passes into the Moon’s shadow. The Earth’s shadow is large, and the Moon’s shadow is small; yet so far the two kinds of Eclipse are really alike.

If you and I were standing on the Sun we should see the Earth eclipse the Moon, and the Moon eclipse part of the Earth, by turns, and in the same way. The Earth would slip in front of the Moon, hiding the Moon from us; or the Moon would slip in front of the Earth, hiding part of the Earth from us.

But looking upon the two sights from the Earth, and not from the Sun, they seem to us a little different in kind.

Other Eclipses take place in the kingdom of the Sun besides these two.

There are many other moons besides our Moon. You should always remember that MOON is the name of our particular moon, just as EARTH is the name of our particular world. Other little worlds travelling with big ones are spoken of as “moons;” but more rightly they ought to be called “satellites.” Each one has its own separate name; whereas our “satellite” has no other name except “The Moon.”

Eclipse of the Moon. January 28, 1888.

Mars has two tiny moons, and Mars often eclipses his moons. Jupiter has five moons, and they often pass into his vast shadow. The eight moons of Saturn, the four moons of Uranus, the moon of Neptune, are all in turn eclipsed. Also, in turn, they all pass between the Sun and the Planet to which they belong, casting a small shadow on the Planet, and making an Eclipse of the Sun for that part where the shadow falls.

One or two other things often seen are much like Eclipses, though known by other names.

For instance, as the Moon journeys at night across the sky--seems to journey, I mean--she blots out star after star on her way.

Does she really blot each star out, as you might snuff out a candle?

No, indeed. She only comes between our eyes and the star. The Moon is still as near as usual, and the star beyond is as far off as usual. But, for a little while, the Moon, being exactly in the line between, hides the star from us.

We do not speak of this as an eclipse, but really it is an Eclipse of the stars by the Moon.

They are hidden by the solid body of the Moon, just exactly as the Sun is hidden during a Total Eclipse. The chief difference is that we look upon the bright side of the Moon, instead of the dark side.

Again, you will sometimes hear of a CONJUNCTION of two planets, or of a planet and a very bright star.

A “Conjunction” means “a joining together.”

Jupiter is seen, in the sky, to come very close indeed to Saturn. We are told that it is “a Conjunction” of Jupiter and Saturn.

Still you must not for a moment think that Jupiter is any closer than usual to Saturn. They are divided, as always, by a great gulf of millions upon millions of miles. The two only happen to be for a while in nearly the same line of sight, as looked upon from the Earth. Saturn is very much farther off, but he is almost behind Jupiter.

Instead of Jupiter and Saturn seeming to draw near together, it may be Jupiter and Venus; or perhaps Jupiter and Mars; or Saturn and the bright star Sirius.

But in each case it is only a seeming nearness. They are not really near together. It is only a matter of the one being seen beyond the other--very greatly beyond it--in almost the same line of sight.

Suppose you stood on the sea-shore and saw a ship one or two miles off sail just between you and another ship ten or twenty miles off. If the near one hid the farther one it would be like an Eclipse. If the near one only appeared to be side by side with, the farther one it would be like a Conjunction.

There is still one more sight, which is also like an Eclipse in its nature. Sometimes one of the planets whose pathway lies nearer to the Sun than the Earth’s pathway glides exactly between the Sun and ourselves.

This is just what the Moon does at an Eclipse of the Sun. But the planet is too far away from us to hide the Sun. We can only see a tiny dark body creeping across the Sun’s face; and we call this a “TRANSIT,” or a “passing over.”

You will hear more about “Transits” in the next chapter.

QUESTIONS.

1. What is an Eclipse?

A hiding of light.

2. Tell me what causes an Eclipse of the Sun.

The round body of the Moon comes exactly between the Earth and the Sun, and hides the Sun from us.

3. Tell me what causes an Eclipse of the Moon.

The round body of the Earth comes exactly between Sun and Moon; and the Earth’s shadow falling on the Moon makes her dark.

4. How far are the two alike?

In an Eclipse of the Sun, the Moon is between Sun and Earth. In an Eclipse of the Moon, the Earth is between Sun and Moon.

5. Do they seem just alike to us?

Not as seen from Earth. In an Eclipse of the Sun we see the Moon’s solid body against the Sun. In an Eclipse of the Moon we see Earth’s shadow crossing the Moon’s face.

6. Does the Moon get nearer to the Sun than usual in an Eclipse of the Sun?

No nearer at all. She only passes between the Sun and Earth.

7. Are there any other eclipses?

Other planets with moons have eclipses in the same way.

8. Tell me another name for “moons.”

Satellites.

9. What is a Conjunction of Planets?

When two planets happen to be seen near together in the sky we call that a Conjunction.

10. Are they really near together?

No nearer than usual. They only happen to lie in almost the same line of sight.

11. What is a Transit of a Planet?

Very much like an eclipse. One of the planets, nearer to the Sun than our Earth, gets exactly between the Sun and Earth.

12. Is the Sun’s face hidden?

No; because the planet is too far away. We only see a small body crossing his face.

13. At what time is an Eclipse of the Sun?

Never at any other time than New Moon.

14. When do we have an Eclipse of the Moon?

Never at any other time than Full Moon.

15. What is a Total Eclipse of Sun or Moon?

When the whole face of the Sun or Moon is hidden.

16. What is a Partial Eclipse?

When only part of the face of Sun or Moon is hidden.

17. What is an Annular Eclipse of the Sun?

When a bright rim of the Sun is seen all round the dark body of the Moon.