Galileo.
Astronomers have discovered a great many things about the shape and the motions of the earth. Before these were understood, people supposed that the earth was still, and was flat instead of round, and that the sun really rose in the east and set in the west; and it seems so to every body now that has not learned what the astronomers have discovered. A bright little boy said to a lady who was teaching him about the earth, You don’t mean to say that the world is round? I know that it isn’t. I can see that it is flat with my own eyes. She assured him that the earth was round, but he could not believe it, and replied, Well, I shall ask my father, for gentlemen commonly know more about such things than ladies do. You will think it strange when I tell you that, a little more than two hundred years ago, people generally believed as this little boy did, and that they put a learned man, named Galileo, into prison because he said that the earth was round, and that it went around the sun.
Why we see only a part of the moon most of the time.
You will want to know something about the motion of the moon. As the earth goes round the sun, so the moon moves around the earth. It takes a little less than a month for it to get round the earth, and it goes around it about thirteen times a year. As I have told you in another chapter, the silvery light which the moon sheds upon us is the light of the sun reflected by the moon. Why it is that only a part of the moon shines upon us much of the time, I will explain to you. When there is a new moon, as it is termed, the moon is in such a position that we can see only a little of that part of it which the sun shines upon. But when the moon is at the full, it is in such a position that we see all of it that is lighted up by the sun. So when the moon quarters, as it is expressed, we see but a half of the lighted portion, and so on. All this is made plain by this figure. S is the sun, E is the earth, and a, b, c, &c., the moon in different positions. When the moon is at a we can not see any of it, because it is between the earth and the sun. The sun shines upon the half of the moon that is toward it, and this half is now all away from our sight. As it leaves a we see a little of it, and a little more every night; and when it gets to b we see a quarter of the part which the sun shines upon. Then, when it comes to c, we see half of it. When it is at d we see rather more than half: it is then called gibbous. When it is at e we can see the whole of the lighted-up part, and so the moon is full. Then at f it is gibbous again, and at g half moon.
Eclipse of the moon explained.
And now you will want to know how an eclipse of the moon happens. This I can make plain to you by this figure. A B is the sun, C D the earth, which is smaller than the sun, and M the moon, which is much smaller than the earth. Now, as the sun shines upon the earth, there is a dark shadow beyond the earth, as represented. When the moon, therefore, happens to pass through this shadow, it is in the dark, and no one on the earth can see it till it comes out from the shadow. While it is in the shadow there is an eclipse, as it is termed.
Questions.—What two things gradually stop the going up of a ball in the air? Could the ball stop of itself? Why can you set yourself going and stop yourself? How is it with dead matter? What is said about the earth? How fast does it move? How do you know about the motion in traveling? Why is it that sometimes, when the cars are going quite fast, you scarcely seem to be moving at all? How is it if you look out? How is it if the cars come to a place where the rails are uneven, or where there is a turn in the road? Give the comparison about looking out of the cars and looking away from the earth. Tell about the mistakes that have been made about the motion of the earth. How is it that day and night are made? Tell about the two motions of the earth. Describe how you would make these plain with a candle and an orange. Why is a day added to every fourth year, making it leap year? What did people suppose about the earth and sun before astronomers found out so much about them? Give the anecdote of the little boy. Tell about Galileo. Tell about the motion of the moon. Tell about the new moon and the full moon. Tell about the eclipse of the moon.