This section is from the "The New Student's Reference Work Volume 5: How And Why Stories" by Elinor Atkinson.
Why we have both day and night following each other regularly once every twenty-four hours, is supposed to be very hard to understand. It isn't explained to children in school until they get their big geographies in the sixth grade. But it's just as easy as anything.
You see the sun rise and set every day. In the evening the sun goes down the western sky—or seems to go down—until it is out of sight. Then it is dark. In the morning the sun seems to rise in the east, and we have day. The sun has motions of its own, but in relation to our earth it stands still. It is the earth that turns away from the sun in the evening, and toward it in the morning. Push a long hatpin through an orange. Now hold the orange by both ends of the pin, and level with the flame of a lamp. Let's play the lamp is the sun, and the orange the earth. You know, of course, that the earth is a very big, nearly round ball. It is about eight thousand miles through the middle and over twenty-five thousand miles around. The lamp stands still, and keeps right on shining. But its light can shine only on the side of the orange-earth that happens to be turned toward it. It couldn't reach around and shine on the other side, and it couldn't shine through the solid earth, now, could it?
Turn the orange-earth over and over, slowly, on the hatpin. That is the way the earth turns. The sun is always shining on one-half of it, but the light half is constantly changing. As the earth always turns eastward toward the sun, the sun seems to travel westward. It takes just one day, or twenty-four hours, for the earth to turn over once, and give all parts day and night. So, when it is noon in the United States the little Chinese boys and girls on the dark side of the earth are fast asleep. And when they are hurrying to school very likely we are undressing to go to bed.