Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site utastro.UUCP Path: utzoo!watmath!clyde!bonnie!akgua!whuxlm!harpo!decvax!genrad!panda!talcott!harvard!seismo!ut-sally!utastro!dipper From: dipper@utastro.UUCP (Debbie Byrd) Newsgroups: net.astro Subject: StarDate: July 8 The Solar Corona Message-ID: <320@utastro.UUCP> Date: Mon, 8-Jul-85 02:00:24 EDT Article-I.D.: utastro.320 Posted: Mon Jul 8 02:00:24 1985 Date-Received: Sat, 13-Jul-85 15:21:55 EDT Organization: U. Texas, Astronomy, Austin, TX Lines: 36 The word corona means "crown" -- and the sun's corona really looks like a crown. More -- after this. July 8 The Solar Corona On today's date in the year 1842, there was a total eclipse of the sun. It became famous for some of the earliest scientific descriptions of the sun's corona. The solar corona is just the tenuous outermost atmosphere of the sun. The corona is visible to us only during a total eclipse, when the black disk of the moon blots out the main body of the sun -- and the corona appears as a lovely encircling shell of wispy white light. Some early astronomers believed that the solar corona was only an optical illusion. But the first photographs of a total eclipse proved that the corona is real. In 1869, scientists used a device called a spectroscope to split the white light of the corona into its component rainbow of colors. Instead of all colors being present, only a few puzzling sharp bright discrete colors were found. Fifty years later this evidence was understood to mean that the sun's outer atmosphere has a much higher temperature than the photosphere, which is the visible surface of the sun. In fact, the temperature of the corona is about two million degrees centigrade, compared to only about six thousand degrees for the photosphere. In other words, as you go up from the visible surface of the sun to the sun's outer atmosphere, things get hotter -- not colder as you might expect. Some combination of magnetic effects and shock waves appears to be transmitting energy from beneath the sun's surface up into the tenuous corona. Script by Deborah Byrd and Harlan Smith. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin