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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: April 24 Nine Months to Uranus
Message-ID: <55@utastro.UUCP>
Date: Wed, 24-Apr-85 02:00:22 EST
Article-I.D.: utastro.55
Posted: Wed Apr 24 02:00:22 1985
Date-Received: Fri, 26-Apr-85 06:49:23 EST
Organization: U. Texas, Astronomy, Austin, TX
Lines: 43


The change in Earth's seasons is fun -- but you might not like the
seasons on Uranus.  More -- after this.

April 24  Nine Months to Uranus

The Voyager spacecraft is now heading for Uranus -- with its closest
approach due exactly nine months from today.  When it gets there, it'll
explore a world that has seasons -- but seasons far different from
those on Earth.

Earth's seasons are caused by our world's tilt on its axis.  Earth's
northern and southern hemispheres take turns in tilting most directly
toward the sun.

The planet Uranus also has seasons that result from that world's tilt
on its axis.  But the change is much more dramatic -- due to the
strange orientation of Uranus in space.

Uranus lies nearly sideways with respect to the plane of its orbit.  It
takes about 84 Earth-years to complete a single orbit around the sun.
For one-quarter of that time -- about 21 years on Earth -- the southern
hemisphere of Uranus has endless sunlight.  Meanwhile, the equator has
perpetual twilight -- and the northern hemisphere, nothing but
darkness.

After another quarter of the Uranian year, this world has changed its
orientation to the sun -- and the sun rises and sets over the equator
of Uranus.  Then, a single day lasts a bit less than 24 hours -- as
long as Uranus takes to rotate once on its axis.  A quarter year later
-- again, about 21 years in Earth-time -- the northern hemisphere faces
directly into the sun.  The equator is in twilight again -- and the
southern hemisphere is sentenced to two decades of darkness.  That's
the situation on Uranus now.  As Voyager approaches Uranus, the north
pole of this world is pointing almost directly toward the sun.


Script by Deborah Byrd.




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