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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: January 14 Jupiter and Comet Halley
Message-ID: <1002@utastro.UUCP>
Date: Mon, 14-Jan-85 02:00:24 EST
Article-I.D.: utastro.1002
Posted: Mon Jan 14 02:00:24 1985
Date-Received: Wed, 16-Jan-85 16:17:20 EST
Organization: UTexas Astronomy Dept., Austin, Texas
Lines: 34

Comet Halley today is closer to the sun than the planet Jupiter.   More
-- in a moment.

January 14  Jupiter and Comet Halley

The planet Jupiter is gigantic -- with gravity so powerful that it can
change the orbit of a comet.  It can greatly shorten a comet's journey
around the sun -- so that the comet returns on the order of tens of
years -- instead of hundreds of thousands.

It's not known for sure if Jupiter changed the orbit of Comet Halley --
but Halley now shows up regularly once in a typical human lifespan.
About every seventy-six years, Comet Halley loops close to the sun --
then travels back out to the far reaches of the solar system.

It so happens that Jupiter and Comet Halley are now nearly the same
distance from the sun -- though the two bodies are nowhere near each
other in space.  Jupiter's average distance from the sun is five point
two astronomical units -- around four hundred and eighty million miles
-- or more than five times the Earth's distance from the sun.  On
Tuesday, Comet Halley is five point one five astronomical units from
the sun -- slightly closer than Jupiter.

What's more, Jupiter today is on the far side of the sun from Earth --
exactly opposite us in the solar system.  If you could look down from
above the north pole of the sun -- you'd see Jupiter, the sun and the
Earth in a straight line today.  Comet Halley doesn't quite fit into
this line-up -- for one thing, it's traveling below the plane of the
solar system right now.  But the comet is roughly on the same side of
the sun as our planet -- and more than five times farther out.

Script by Diana Hadley and Deborah Byrd.

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