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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: September 22 The September Equinox
Message-ID: <746@utastro.UUCP>
Date: Sun, 22-Sep-85 02:00:20 EDT
Article-I.D.: utastro.746
Posted: Sun Sep 22 02:00:20 1985
Date-Received: Wed, 25-Sep-85 09:18:04 EDT
Organization: U. Texas, Astronomy, Austin, TX
Lines: 37

A good day to celebrate -- the first day of autumn.  More on the
September equinox -- when we come back.

September 22  The September Equinox

Today would have been a special day to the ancient stargazers -- and
it's still a good excuse to celebrate.  It's the September equinox --
one of two days each year when the sun crosses the celestial equator.

The celestial equator is really just an imaginary line drawn around the
sky -- directly above the equator of the Earth.  Today the sun crosses
this imaginary line, which means the sun today is seen directly above
our planet's equator.  After today, the sun will continue to shift its
path across the sky toward the south.  Its rays will strike the
northern hemisphere less directly -- and winter will come to our half
of the globe.  Meanwhile, on the southern half of the Earth, people
today are celebrating the first day of spring.

The equinox was an important day to people long ago.  They didn't have
calendars.  Instead they watched the skies for signs of the changing
seasons.  Once they understood the equinoxes and solstices, the
ancients had the rudiments for making the first calendars.

The two equinoxes and two solstices were observed by the ancients --
but they weren't understood as we understand them today.  Today we know
that the sun shifts its path across the sky because Earth orbits the
sun -- and because Earth tilts on its axis by some 23 and a half
degrees.  As we journey around the sun, the tilt of the Earth causes
the path of the sun to appear to shift toward the north -- then toward
the south in our sky.



Script by Deborah Byrd.


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


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