dipper@utastro.UUCP (Debbie Byrd) (03/17/86)
The moon casts a shadow into space. More on the shape of that shadow -- after this. March 17 The Ice-Cream Moon Tuesday the moon is at first quarter -- when it appears as a half-lit circle of light in our sky. At twilight tonight you'll find the moon high in the south. When you see the moon tonight you might think about something that's always there in space -- yet we on Earth experience it directly only on very rare occasions. That's the shadow cast by the moon. The moon's shadow stretches for hundreds of thousands of miles in space -- always in a direction away from the sun. Like the shadows cast by all objects -- from planets to your hand -- -- the lunar shadow has two parts. The darker central part of the shadow is called the umbra. The lighter part surrounding the umbra is called the penumbra. The moon is a round ball in space -- which means the darker umbral shadow of the moon is shaped like a cone. When you see the moon half-lighted in our sky tonight and Tuesday, you might find it fun to think of the moon as a scoop of ice cream -- complete with a cone -- the cone-shaped shadow of the moon. Other planets and their round moons also cast cone-shaped shadows. We're not conscious of these shadows that trail out into space until another object wanders into them. Then there is an eclipse. This coming April 24, we'll have the chance to see the shadow of our own planet -- when the moon passes through it. Parts of the total lunar eclipse will be visible all across the United States -- but west of the Rockies, people will see the moon blood-red in the shadow of the Earth. Script by Diana Hadley. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin