dipper@utastro.UUCP (Debbie Byrd) (05/30/85)
There are three distinct regions in the atmosphere of the sun. We'll tell you what makes one region different from another -- after this. May 30 The Sun's Atmosphere On Earth, there's a place where the atmosphere leaves off -- and the surface of the planet begins. But the sun is made entirely of gases. It has no distinct line separating the atmosphere from what's below it. And yet, there are three general regions in the sun's atmosphere. The innermost one is called the photosphere. Nearly all the heat and light which reaches us is radiated from this region -- which is so bright that it obscures the two levels of atmosphere above it. Directly above the photosphere is a thin layer called the chromosphere. Its name is from the Greek word meaning "color." Observers in the 17th century described a reddish "fringe" around the sun during total solar eclipses. This reddish fringe is the chromosphere. Above the chromosphere is the solar corona. That name comes from the Latin word for "crown." Like the chromosphere, the corona only appears when the sun is blotted out. During the brief moments of a total eclipse of the sun, the body of the sun disappears behind the body of the moon -- the sky darkens -- and the wispy corona stands out like a ring of white fire. A mystery surrounds these layers of the sun. Although the density of the gases decreases as you go outward from the photosphere, the temperature increases. The photospheric temperatures are about six thousand degrees, while the temperature climbs through the chromosphere -- and soars to several million degrees in the corona! Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin