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From: dipper@utastro.UUCP (Debbie Byrd)
Newsgroups: net.astro
Subject: StarDate: October 2 The Pole Star
Message-ID: <5@utastro.UUCP>
Date: Wed, 2-Oct-85 02:00:23 EDT
Article-I.D.: utastro.5
Posted: Wed Oct  2 02:00:23 1985
Date-Received: Sun, 6-Oct-85 04:47:51 EDT
Organization: U. Texas, Astronomy, Austin, TX
Lines: 40

The north star, Polaris, stays fixed to one spot in our sky -- well,
almost.  More -- after this.

October 2  The Pole Star

There's a star in the north right above Earth's axis, the imaginary
stick that our world spins around.

This special star is called Stella Polaris.  It's the north star, or
pole star.  As Earth turns, the stars wheel across the night sky.  They
rise and set below the horizon.  But Polaris lies at the hub of the sky
-- as though it's at the hub of a wheel -- or the hole in a record.
The north star stays fixed in a spot due north.  It's visible every
night throughout the northern hemisphere.

The pole star stays in one spot in our sky -- but not precisely.  If
you took a picture of this star -- set your camera on a tripod and left
the shutter open for some hours -- you'd see that the star is actually
moving in a tiny circle in the northern sky -- a circle somewhat larger
than the full moon.  Polaris isn't precisely at the celestial pole.
Instead, it's less than a degree from the pole.

But the north celestial pole is moving closer to Polaris, due to
another motion of Earth called precession.  The precession of the Earth
is a 26-thousand-year cycle.  It causes the north celestial pole to
trace out a great circle among the stars.  Thuban was the pole star to
the builders of the Pyramids.  Before that, Vega was the brightest star
in the vicinity of the pole.  Our Polaris will be closest to the pole
in about the year 2100.  Then the pole will drift away from the star --
to return in another 26 thousand years.





Script by Deborah Byrd.



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


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