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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: September 14 Comet Duet
Message-ID: <716@utastro.UUCP>
Date: Sat, 14-Sep-85 02:00:19 EDT
Article-I.D.: utastro.716
Posted: Sat Sep 14 02:00:19 1985
Date-Received: Tue, 17-Sep-85 05:12:27 EDT
Organization: U. Texas, Astronomy, Austin, TX
Lines: 37

Two famous comets are near each other on the dome of the sky tonight.
More -- in a moment.

September 14  Comet Duet

Two comets appear very near each other on the dome of the sky tonight.
Neither one is bright enough to be seen without a telescope -- but
you've probably heard of them both.

The comets are Giacobini-Zinner and Halley.  Just a few days ago the
first spacecraft ever to visit a comet passed near Giacobini-Zinner.
Next March several more spacecraft will encounter Comet Halley.

Both of these comets have orbits that are steeply inclined to the
ecliptic, or plane of Earth's orbit around the sun.  But Halley and
Giacobini-Zinner have very different paths through the solar system.
Giacobini-Zinner moves around the sun once every six-and-a-half years.
It passed closest to the sun on September 5th -- and is now heading
outward in the solar system.

Comet Halley, on the other hand, is now moving toward the sun.  It
travels around the sun in the opposite direction to Giacobini-Zinner.
Right now Giacobini-Zinner looks about forty times brighter than Halley
-- and its apparent position against the stars is changing more rapidly
-- since this comet is now closer to the sun and the Earth.

But, though they're not really near each other in space, tonight both
comets appear close together in the sky -- in the vicinity of the club
of the hunter in the constellation Orion.  At their closest, they'll be
about two degrees apart on the dome of the sky -- about four times the
diameter of the moon.  Again, you'd need a telescope to see the
comets.  But if you did see them, you'd be looking at the two most
famous comets in history.

Script by Diana Hadley.

(c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin


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