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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: March 31 The Galactic Carousel and the Cosmic Year
Message-ID: <19@utastro.UUCP>
Date: Sun, 31-Mar-85 02:00:26 EST
Article-I.D.: utastro.19
Posted: Sun Mar 31 02:00:26 1985
Date-Received: Fri, 5-Apr-85 08:57:33 EST
Organization: U. Texas, Astronomy, Austin, TX
Lines: 37

Our sun is a star revolving around the center of the galaxy.  More --
after this.

March 31  The Galactic Carousel and the Cosmic Year

Our Milky Way galaxy is a flattened disk of stars -- with long starry
arms spiraling away from a bright bulging center.

Our sun is just one of many hundreds of billions of stars in the Milky
Way.  Like all the other stars in the galaxy, the sun -- with its
family of planets including Earth -- revolves around the galactic
center.  One circuit of the galaxy takes us about two hundred and forty
million years.

As the sun circles the center of the galaxy, it also bobs up and down
with respect to the galactic plane -- the disk of the galaxy, where
most of the stars are.  The sun moves up and down -- and around -- like
a wooden horse on a carnival carousel.

One or two million years ago, the sun crossed the galactic plane moving
northward, toward the north pole of the galaxy.  About ten million
years from now, after gradually slowing down, the sun will reverse
direction -- travel back towards the plane of the galaxy -- and cross
back to the other side.  A complete up and down cycle takes about 66
million years -- so during one trip around the galaxy, the sun crosses
the galactic plane about eight times.

Look low in the south in the evening at this time of year -- and you'll
be looking backwards in our journey around the center of the galaxy.
Again, it takes our sun about two hundred and forty million years to go
once around the galactic center -- a time interval which astronomers
call the cosmic year.

Script by Diana Hadley and Deborah Byrd.


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