dipper@utastro.UUCP (Debbie Byrd) (12/20/85)
This is the anniversary of the discovery of Comet Giacobini-Zinner. More -- after this. December 20 The Discovery of Comet Giacobini-Zinner Many comets grace our skies each year. Most of them never become bright enough to be seen with the naked eye -- or become as well-known as Comet Halley. One comet that did become famous this year is Comet Giacobini-Zinner -- which never gets bright enough to be seen without a telescope. Last September Giacobini-Zinner became the first comet to be visited by a spacecraft. I.C.E. -- the International Cometary Explorer -- flew within five thousand miles of the comet's core -- passing within the immense cloud of debris and gases surrounding the core. It was on today's date in in the year l900 that a French astronomer named Giacobini discovered the comet. Astronomers watched it for two months before it became too faint to see. Its orbit was calculated as just a little OVER six and a half years. The next time the comet came near the sun, the Earth wasn't in a very favorable position for observers to be able to see it. When the comet showed up again, in 1913, astronomers didn't recognize it as the same comet. It appeared about six months too early. In Germany an astronomer named Zinner was the first to see the comet at the 1913 return. After astronomers observed the comet for awhile, someone suggested that Zinner's Comet was the same one that Giacobini had seen thirteen years before. Additional calculations showed that it was the same comet -- and that it orbited the sun in just UNDER six and a half years. Both astronomers got the credit for the comet -- and it got the double name Giacobini-Zinner. Script by Diana Hadley. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin