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Judy Tarbets age 14, of Tujunga, California, for her question:

How does the little moon eclipse the big sun?

A distant mountain looks smaller than a nearby hill. The little hill seems wider and higher than the far off mountain. In fact, if the little hill is between you and the mountain, the dwarf may completely hide the giant from view.

But, as you walk towards the mountain, it seems to grow bigger. Behind you the hill seems to grow smaller. When you are halfway between them you see the giant and the dwarf in their proper proportion. This is because objects seem to shrink with distance. The further away an object is the smaller it seems to be.

Compared with the giant sun our little moon is a midget. They both look to us like yellow coins hanging up there in the sky. Actually, the moon and the sun are both globes. We see one side of each globe and it looks like a disk. We measure these globes by their diameters ‑ 2 line from edge to edge clear through the middle.

The diameter of the giant sun is 366,000 miles ‑ more than 100 times the diameter of the earth. The diameter of the moon is 2,163 miles ‑ which is about one four hundredth the diameter of the sun. If we had 400 moons and one half a moon lined up side by side they would equal the diameter of the sun. Yet, when we have an eclipse of the sun, our one little moon gets in front of the sun and completely covers the giant.

But the sun plays the role of the faraway mountain. And the moon acts like the little nearby hill. If we were on a space ship halfway between the sun end the moon we would see these two heavenly bodies in their proper proportions. The sun would looks as it actually is, 400 times larger than the moon.

From the earth, however, the little moon looms large as the sun because it is so much closer than the sun. The sun is about 93,005,000 miles away from us. The distance of the moon from the earth varies between 222,000 and 253,000 miles. At the time of eclipses the big sun is about 400 times farther away from the earth than is the moon. This extra distance makes the sun seem to shrink. It appears to be the same size as the nearby, much tinier moon.

The solar eclipse occurs when the moon is new and when it is between us and the sun. We get a new moon, but not an eclipse, every month. This is because the moon's orbit varies. The moon may pass north or south of the sun. What's more, to make a total eclipse, the moon must be close enough for its long, tapering shadow to fall upon the earth.

The average length of the moonts shadow is 232,000 miles. To make a total eclipse, the moon must be at least this close to the earth. Otherwise the eclipse is only partial, or annular. In an annular eclipse, the moon is a little too far away from us to cover the disk of the sun completely. The moon covers only the center of the sun, leaving a brilliant border of radiance around its dark disk.

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