Kathleen Fitzgerald, age 9, of Albany, N.Y., for her question:

Does the Earth have a shadow?

Wherever you go, your faithful shadow goes with you. Sometimes it gets lost in the darker shadows around you and you do not see it. Sometimes it is taller than you are. If our whopping world has a shadow, surely it must be a whopping whale of a shadow.

Our solid Earth has an enormous shadow that is almost one million miles long. It is created because the bulky globe cuts off some of the golden light coming from the sun. The daytime side of the Earth faces the sun, and the nighttime half faces away from the sun in the opposite direction. Naturally, the long shadow points away from the nighttime side of the globe.

You would expect the shadow of the round Earth to be round, and so it is. Near the ground it is about 8,000 miles wide, which is the same as the width or diameter of the solid round globe. But as it points on and out into the starry sky it gets narrower and narrower. The shadow of the Earth is shaped like a long tapering cone. The pointing finger of shade reaches way past the path of the orbiting moon. After about 900,000 miles it ends in a slender point.

You can see your shadow when it falls on the ground or on a wall or on some other solid object. We do not see the shadow of the Earth pointing up and out into the night. This is because it usually does not fall upon solid objects out there in the empty spaces of the sky.  Once in a while this rule is broken, however, when the Earth's shadow falls upon a solid object in the sky and we get a chance to see it.

This happens when we have an eclipse of the moon. Every month the moon orbits in a circle around the Earth. Sometimes its path goes through the Earth's shadow. Then we can watch the shadow of the Earth creep inch by inch across the golden face of the moon. The edge of the shade is curved because the round Earth casts around shadow.

Out near the moon, the Earth's shadow is much narrower than our big globe. But it is still much wider than the moon. It may take the moon five or 10 minutes to pass through the shade. When it crosses through the widest part the moon may be eclipsed by the Earth's shadow for an hour and 40 minutes. During the eclipse, the dusky shadow dims the bright moon and changes its golden yellow to coppery red.

The moon circles all the way around the Earth once every month. The Earth's shadow always points from the night side of the Earth. You would think that the moon must pass through this shadow with every orbit and give us an eclipse every month. But this does not happen. The moon travels in a wobbly orbit, and as a rule, it passes above or below the shadow of the Earth. We may get one or two or three eclipse in a year, and some years there are none at all.