Part 14

"Eclipsed means hidden," said Mary, laughing. "If Uncle Robert stands right in front of you, as he is doing just now, he hides me from you, so I am eclipsed."

"Very true," said Uncle Robert, laughing heartily at the hint. "Planet Mary is eclipsed by Uncle Robert, and poor little Planet Harry cannot see her till Uncle Robert gets out of the way." This he immediately proceeded to do, and next moment he was pursuing Fido, who was having a not over-friendly encounter with a strange cat in a neighbor's garden.

"Oh, dear," said Harry, in distress, "where were we? We were up in the sky among the planets, and now Uncle Robert has brought us back again to earth. Do listen to poor Fido." He certainly seemed to be getting the worse of the encounter with Pussy; but when Uncle Robert came to the rescue the enemy vanished, and Fido, nothing daunted, went in search of other prey. When peace and quiet were once more restored, Mary resumed her story.

ECLIPSE OF JUPITER'S MOONS.

"Do you know, the appearance and disappearance of the little moons of Jupiter once gave a great deal of trouble to astronomers. They had a way of appearing a little too soon or a little too late. They were very seldom on time. This was very provoking, as astronomers were rather proud of being able to tell exactly when these little moons could be seen. At last they found out what was the matter, and that they were to blame and not the moons. We see the little moons on account of their light, and light takes time to travel. Don't you remember, I told you sound travels a mile in five seconds. Light travels even more quickly, for it only takes a little over a second in coming to us from the moon. It takes about eight minutes in coming to us from the sun; but Jupiter is about five times as far away from us as the sun, so that light takes about half an hour in coming to us from Jupiter. We do not see it as it is, but as it was more than half an hour ago, when its rays of light started out to Planet Earth.

"Now, Jupiter, in going around the sun, is sometimes on the same side of the sun as we are. Then the light from the moons reaches us in about thirty-two minutes. But when Jupiter is on the opposite side of the sun, and as far away from us as it can be, then light takes as much as forty-eight minutes in coming here--over a quarter of an hour longer. So a clever astronomer decided that when Jupiter and his moons are nearest to us, it does not take as long for their light to reach us as when they are farther away, and this is because light, like sound, must have time to travel.

"Even though light can go round the earth seven times in a second, traveling at the rate of about 186,000 miles a second, yet, as Jupiter is millions of miles away, it takes light about half an hour, and some times forty-eight minutes, for it to cross that great distance. It is just the same as if Uncle Robert were in India. It would take him a much longer time to come and see you than if he were at his home just a few hundred yards away. It takes time for him to travel here, just as it takes time for light to travel from the little moons of Jupiter."

"I wish we had five moons shining on our earth," said Harry; "how pretty it would be! Does it take the moons as long as our moon to get around Jupiter?"

"They are much livelier than our moon," replied Mary; "and the second moon flies right around Jupiter in a little more than a day and a half, and even the outside moon only takes about two weeks; so there must always be a moon shining in the sky for Jupiter. These moons, except the moon discovered by Professor Barnard, are all larger than our moon, and the fourth one is nearly as large as Mars. But I hear the bell for lunch, Harry, and I must run away now. I will tell you about the other planets later."

"How many are there?" said Harry, as his sister kissed him good-by.

"Only three," replied Mary; "and I shall tell you about them to-morrow, if you are not too tired."

"Too tired!" said Harry. "I am never too tired to listen to you."

JUPITER.

Oh! that it were my doom to be The spirit of yon beauteous star, Dwelling up there in purity, Alone, as all such bright things are; My sole employ to pray and shine, To light my censer at the sun!

Moore: Loves of the Angels.

A LESSON IN ASTRONOMY.

The solar system puzzled us, Miss Mary said she thought it would, And so she gave us each a name, And made it all into a game, And then we understood.

Theresa, with her golden hair All loose and shining, was the sun, And 'round her Mercury and Mars, Venus, and all the other stars Stood waiting, every one.

I was the earth, with little Nell Beside me for the moon so round, And Saturn had two hoops for rings, And Mercury a pair of wings, And Jupiter was crowned.

Then when Miss Mary waved her hand, Each slow and stately in our place, We circled round the sun until A comet, that was little Will, Came rushing on through space.

He darted straight into our midst, He whirled among us like a flash, The stars went flying, and the sun, And laughing, breathless, wild with fun, The "system" went to smash.

--Youth's Companion.

THE GIANT PLANETS.

THE PLANET SATURN.

Harry had spent a most delightful evening looking through Uncle Robert's telescope at the little moons of Jupiter, and he also had seen the planet Saturn, with its rings and moons. Next evening when his sister came to talk with him he had many questions to ask her. First of all he wanted to know what the rings were made of.

"Millions of little moons," replied his sister. "I wish you could see Saturn and its rings through the great telescope at the Lick Observatory. It makes such a pretty picture. Like Jupiter, the planet Saturn is surrounded by clouds; but they are tinted with blue at the poles, yellow elsewhere, and dotted here and there with brown; purple, and red spots. Around the center is a creamy white belt. Then, there are eight moons that accompany Saturn in its journey around the sun; but they give very little light to the planet, since if they could all be full together they would give but a sixteenth part of the light we receive from the moon."

"Why is that?" asked Harry.

THE PLANET URANUS.