Welcome to You Ask Andy

Jeff Snyder, age 12, of Spokane, wash., for his question:

Does the moon rotate?

Yes, the moon does rotate on its axis, but it spins very, very slowly. The earth, of course, rotates every 24 hours. This wives us our day and night because first one side, then another side, is facing the sun. The side facing away from the sun is in the shadows of night. The moon, too, has a day and a night as first one side, then another, faces the sun.

From the earth, we always see the same side of the moon. This seems to contradict the fact the moon rotates. If it spins around, surely we should bet to see all sides of the moon as it turns. This is not so and for a very good reason. The moon's rotation equals its revolution ‑ and that fancy statement, says Andy, needs some explanation.

The rotation of the moon or any heavenly body is, of course, the spinning around on its axis. It rotates like the spinning of a tope The revolution of the moon or any heavenly body is the journey around its orbit. The moon revolves in an orbit around the earth. The earth revolves in an orbit around the sun.

The earth rotates about 365 times while it is revolving onto around the sun. The moon rotates only once while it revolves once around the earth. Its rotation, then, equals its revolution.

That statement still sounds a little grandish, so let's act it out to make sure we know how it is done. You will need a floor lamp placed in the center of the room. Move the furniture so that you can walk clear around the lamp without tripping.

 The floor lamp will play the role of the earth. You  will play the role of the moon. You are going to make one revolution around the earth. face the lamp and step three paces back. Keep this distance as you make your orbit. Notice which wall of the room you are facing when you start out. Now start to orbit around the lamp, keeping your  face toward it. To do this you will have to walk sideways.

Stop a moment when you are quarter way  around. Notice that you are now facing a different wall. This means that your body has made a quarter turn, you have revolved a quarter turn on your axis.

At the half‑way point around your orbit you will be facing the wall opposite from the one you faced. first. You will have rotated a half turn on your axis. Keep going until you are back where you started. You did what the moon does every 27‑1/3 days. End because your f ac© was toward the lamp at all times, your body made a complete turnabout as you went around your orbit.

This little experiment is, of course, over‑.simple. It shows only one movement of the earth and the moon. For meantime, tie earth has rotated on its axis 27‑1/3 times. What's more, the earth and the moon are traveling together in an orbit .!round the sun. In one month, one lunar revolution around the earth, they traveled about one twelfth of their orbit around the sun at a speed of some 18‑1/2 miles a second.

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