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From: nyssa@abnji.UUCP (nyssa of traken)
Newsgroups: net.astro
Subject: Re: StarDate: April 24 Nine Months to Uranus
Message-ID: <603@abnji.UUCP>
Date: Mon, 29-Apr-85 07:32:07 EDT
Article-I.D.: abnji.603
Posted: Mon Apr 29 07:32:07 1985
Date-Received: Tue, 30-Apr-85 05:19:15 EDT
References: <55@utastro.UUCP>
Organization: Terminus Hospital, Incorporated
Lines: 59

>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

When I read this, it seemed a bit misleading.  As Uranus moves around its 
orbit, one hemisphere gradually lightens and one gradually darkens.  In
fact, most of the time, most of the planet will get sunlight in a given day.

On earth, the seasons above the Arctic circle do not change in quantum,
and only at the pole is there the 6 month day/6 month night.  The farther
south you get, the shorter the "endless" day/night, until, eventually,
the Arctic circle, where there may be a single day when the sun doesn't
set.

In the case of Uranus, the Arctic circle is much farther south, so
this effect is more pronounced.
-- 
James C Armstrong, Jnr.   ihnp4!abnji!nyssa

Chap with wings there, five rounds rapid!