Part 19

"The lamp is so bright without a shade that it blinds me when I try to see the picture beyond it," said Paul.

"Oh, I see! I see!" said Betty, beginning to hop up and down. "Can I tell, Uncle Henry?"

"Surely," laughed Uncle Henry, "what do you see?"

"When Paul faces the picture with his back to the lamp," said Betty, "it's night on his face, and day on the back of his head! Is that right?"

"Yes, go on," encouraged Uncle Henry.

"And so he can see that picture better, 'cause the lamplight isn't in his eyes. But when he faces the lamp and looks across it, then it's day in his face, and night on the back of his head, and he can't see the picture beyond the lamp very well, 'cause the sun-lamp shines in his eyes."

"So that's why we can only see the stars at night!" said Peter.

"Yes, that's why the moon and the stars come out only when it gets dark," said Uncle Henry. "You see the earth turns round and carries us to its dark side, the side that is away from the sun. We say 'The sun has set.' Then when the sun glare is gone from our eyes we can see the sky-pictures, just as Paul sees one picture better with his back to the lamp than he does the other when he has to look through the lamp-light toward it."

"And the stars are in the sky all day long, whether we see them or not?" asked Paul.

"Certainly," said Uncle Henry. "If you could look up at the sky from the bottom of a very deep well, or a tall chimney, so that the sun-light was kept out of your eyes, you could see the stars shining in the daytime. There is a long deep tunnel in the great pyramid of Egypt that goes up and out from the centre of its base toward its north side at just the right angle so that the ancient Egyptians could always see the pole star through it--no matter whether it was night or daytime. You see the pole star never rises or sets, because it is always right over the end of the axis that the earth spins on."

This picture shows how the tunnel in the great pyramid always pointed to the north star because the tunnel is always parallel to the axis the earth spins on.

When the pyramid was built, the star in the tip of the little bear's tail was not the pole star, as it is now. At that time the star that was nearest the pole was one of those in the dragon. Since the pole of the earth goes round in a complete circle among the stars every 25,000 years, the star in Draco will some time be the pole-star again--in, say 20,000 more years!

Peter had picked up the Almanac that Uncle Henry had borrowed from Katy and suddenly cried,

"Oh, Uncle Henry, the Almanac has a lot of the Star People in it. It calls them 'The Signs of the Zodiac.' What's the Zodiac, Uncle Hen?"

"We are going to find out right away, Pete," said Uncle Henry, "but first we must draw pictures of the twelve star folks that are the Zodiac signs. That means three drawings apiece. Pull up your chairs to the table and we'll draw on the sheets of scratch paper with Betty's colored pencils. Paul, you do the Virgo, Leo, and Cancer the Crab; Peter will draw Gemini the Twins, Taurus the Bull, and Aries the Ram; Betty will do the Fishes, called Pisces in Latin, Aquarius the Water Carrier, and Capricornus the Goat; while I will draw Sagittarius the Archer, Scorpio, and Libra the Balance. All old friends of ours."

"We'll put the Almanac here in the middle of the table where we can all see it while we copy the 'signs,' one on each sheet of paper."

Everybody was very busy indeed for about half an hour. At the end of that time the twelve rough drawings were done and pinned up at equal distances apart around the walls of the playroom, three on each of the four walls. They were arranged around the room in the same order in which Uncle Henry had assigned them. The room then looked like this, though of course you see only three walls in a picture. You must imagine how the fourth wall looked.

"Now Paul, suppose you walk around the table again, spinning on your own axis as you go, and we'll try to find out what the Zodiac is. You notice that the pictures are all pinned on the walls at the same height from the floor, which is just the height of the electric lamp bulb, and just the height of Paul's head too, no matter where he is in his walk around the lamp. The twelve constellations, or signs of the Zodiac are in the real sky also on the same level with the earth and the sun, no matter where the earth is in its journey round the sun. Astronomers say it this way: they say that the earth revolves around the sun 'in the plane of the ecliptic.' That simply means that if the sun was in the centre of an enormous horizontal pane of glass, the earth and all the signs of the Zodiac would also always be touching the pane of glass, which would then represent the 'plane of the ecliptic.' Put an l in 'pane' and you have 'plane.'"

"Is each sign for a month?" asked Peter. "I see there are twelve of them."

"That's correct," said Uncle Henry, "and you want to notice that as Paul walks round the lamp and looks across it at the signs on the wall beyond it, the lamp seems to Paul to move from one picture to the next."

This picture is drawn as if the ceiling of the room was taken off and you could look down on Paul walking around the lamp.

When it is January first, Paul, representing the earth, is in the position marked A, nearest to the picture of Gemini behind him, while the lamp, representing the sun, appears to him to be entering the sign of the Zodiac called Sagittarius, directly opposite across the room. Later, on April first, after three months, Paul, or the earth, has traveled a quarter of the way around the sun, has passed the pictures of Cancer and Leo on the wall behind him, and stands nearest Virgo in the position marked B. The lamp has also seemed to move through a quarter circle, has passed through the signs of Capricornus and Aquarius, and appears to Paul to be just entering the sign of Pisces, or the Fishes. In the same way the earth moves through a sign of the Zodiac every month and the sun, while really motionless, appears to also travel through a sign every month. Of course we cannot see the sign or constellation, where the sun appears to be, at the same time we see the sun, for his brightness makes the stars invisible, but if we could see the constellations by day, the sun would appear to travel from one sign of the Zodiac to the next every month.

Here is a clock of the year which shows the earth at one end of the hand, the sun in the middle, and at the other end of the hand an arrow, which points to the sign of the Zodiac where the sun appears to be, and to the date when it seems to be there to an observer on the earth. Draw the hand with the earth-end in several different positions and you will see that the sun, if viewed from the earth, would appear to be in the sign of the Zodiac exactly opposite.

When the children all understood the way the Zodiac divides the yearly path of the earth into twelve equal parts, Betty said, "I want to know why the geography globe at school always looks just as if it was going to tip over."

Uncle Henry laughed. "If you think the geography globe looks unsteady because its axis of iron rod is on a slant, what will you think about the earth when I tell you that it spins around in just the same slanting position, with only an imaginary line for axis?"

"Does it really?" asked Betty.

"Yes," said Uncle Henry, "and it spins so steadily in that slanting position that the north end of its imaginary axis always points toward the same place, a point very close to the north star, or Polaris as it is called."

"Polaris is named for the North Pole, I suppose," said Peter.