Part 9

I do not know, father.

If it rise four minutes earlier every day when will it be an hour earlier?

In half-a-month; and twenty-four hours earlier in twelve months. But that is the time when it will be visiting at night again.

So you have ascertained that the stars go an apparent journey round the earth in a year; like as the sun takes a year to go his apparent course among the stars.

Then both must have the same cause. As I found the daily motion of the stars was owing to the real daily motion of the earth, I suppose this yearly motion of the stars must be caused by some yearly motion of the earth.

Either the sun turns round the earth once a year, or the earth does round the sun.

Well, father, the sun appeared also to turn round the earth once a day. I do not think I could run round the deck in two minutes while I am two hours doing it. Then, as I am satisfied it did not have a daily motion, I am the more disposed not to trust to this apparent yearly motion. It is more likely, too, that the little world should run round the great sun, than that the great sun should revolve round the earth.

I perceive you are as settled upon the annual or yearly motion as you were upon the diurnal or daily revolution.”

THE SEASONS.

“James, my boy,” said Mr. Marple “do you know why there should be winter and summer?

No, father, I really cannot tell. I know that in England the sun was higher up in the day, and that he stopped up longer in summer than in winter. But then as I believed that the sun ran about as he liked, I was not surprised at his change of place. Now, however, I am very anxious to know more about this subject.

When were we in the circle of the Pleiades, that is, the place where at some time or other of the twenty-four hours they would be overhead?

O, that was long before we got to the equator.

Yes, it was about 1500 miles to the north of us. Now we are in the circle of the Virgin cluster.

But the Bull and the Virgin belong to the twelve constellations, of which we were talking, forming a broad circle, along which the sun appears to travel.

True. But they are not in an upright circle. Their line will cross our equator Line.

If that be it, the sun does not appear, then, to go round us over the equator.

No; for if it did, it would be seen overhead at that place every day at twelve o’clock; whereas it shifts its course continually. One day it is over one part at noon, and upon another day over another part.

Why, if the circle of the Zodiac be inclined to the circle of the equator, it will cross it in two places. I suppose that is the reason why, on the celestial globe, one constellation, as the Virgin, is over the equator circle; others, as the Bull, over some place to the north of it; and some others, as the Scorpion, to the south.

You guess rightly.

Then if that be it, the sun must appear to cross the equator twice in the year.

It does so on the 21st of March and 23rd September. These are the vernal or spring equinox, and the autumnal equinox. March is the vernal equinox of London, or equal day and night in spring; but it is the Australian autumnal equinox. In September the Australias have the spring equinox, and the English the autumnal. The sun is seen overhead to the furthest north on the 21st of June, and to the furthest south on the 21st of December.

Why, the first is the summer of England, and the last the winter. Then I suppose that is the reason why in summer the sun looks so high up at noon. Then in winter, as it is shining more over parts south of the equator, the north would neither see nor feel so much of him.

That is correct. You now see why the Australian summer is at the time of the English winter.

Yes, father; because they are on opposite sides of the equator. But you know that the sun does not really move about like this. I want to know what does move.

The earth, to be sure.

I understand that; but neither the rotundity nor motion seems to explain this mystery of the Zodiac. But let me see. When the world swings round the master light, is it obliged to keep bolt upright--north pole up and south pole down?

How would your equator then be, James?