Suppose you had a huge hollow ball the size of the Sun. And suppose you wished to run through that hollow ball a very, very long knitting-needle--eight hundred and fifty thousand miles long--so as just to go from side to side of the huge ball. And suppose upon that big knitting-needle you wished to string a great many Earths or Moons, exactly like our Earth or our Moon, as large beads might be strung close together upon a wire. How many worlds, the size of our Earth, do you think you would need to reach all through the Sun from side to side? And how many worlds the size of our Moon? You would want more than one hundred Earths. And if, instead of Earths, you chose to string Moons on the big needle, you would need more than four hundred Moons. These would not fill up the enormous hollow ball. They would only reach through in one straight line from side to side, showing the _diameter_ of the Sun. Now try again to think of the Moon as a tiny ball, softly bright on one side, only one inch through; and of the Earth as another ball, shining on one side, four inches through. Think of them, if you like, as a large grape and a small cocoa-nut made of silver. Then take the same measure for the Sun, letting one little inch do duty always for two thousand miles. The Sun must dwindle and dwindle in size till every two thousand miles in him has become a single inch. We shall then have a huge ball, or balloon, four hundred and twenty-six inches, or some _thirty-five feet_, through, from side to side. Thirty-five feet is a great deal more than four inches. _One_ foot is twelve inches long. You have seen many a tall man close upon six feet in height. This balloon, to picture the Sun, must be so large that six tall men might be put inside it, one upon the head of another. The whole string of six tall men would about make the through measure of the globe. So we have a Moon the size of a large grape, an Earth the size of a small cocoa-nut, and a Sun the size of a balloon big enough to contain six men in a long row, one upon another. The two little balls would shine softly, on one side only; but the large balloon should be exceedingly brilliant and dazzling all round. If the Moon is so tiny and the Sun is so huge, how is it that they seem to be the same size in our sky? Because of the very great difference in their distance from us. The Moon is near; the Sun is far away. Suppose you are looking at a man near at hand and at a house miles away; which seems to you the bigger? Of course the man, because he is so close. Yet really the house is much the larger of the two. The Moon is only about two hundred and forty thousand miles off; but the Sun is about ninety-two millions of miles away.