dipper@utastro.UUCP (Debbie Byrd) (03/01/86)
If you're out in the country after sunset, you might see the zodiacal light. More -- after this. March 1 The Zodiacal Light If you're out in the country after sunset, be sure to look in the western sky for a strange thin pyramid of light rising from the place on the horizon where the sun set earlier. It'll be pretty dark outside -- the sky will be speckled with stars -- and the sun will be long gone. You might be tempted to think that this pyramid of light is an extension of twilight -- but it's not. It's what's called the zodiacal light. Many people never see the zodiacal light because it must be seen from the country. This time of year is the best time to look for the light in the evening -- but it can also be very conspicuous in late summer, in the east before dawn. The zodiacal light can be breathtaking against a dark sky -- and brighter than the winter Milky Way. It extends in a hazy cone about 30 degrees up from the horizon. Its color is bluish or milky white. Most people who do see the zodiacal light mistake it for the glow of twilight. But the light has nothing to do with twilight, which is caused by sunshine scattered through the atmosphere around our planet. The zodiacal light originates in outer space. It's caused by the sun's reflection off dust grains that move in the plane of the solar system. Like tiny planets, these dust grains orbit the sun. Because they lie in a flat plane, we see the light reflected from the grains in a long, thin band -- above the horizon in the place where the sun set an hour or so earlier. Script by Deborah Byrd. (c) Copyright 1985, 1986 McDonald Observatory, University of Texas at Austin