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From: dipper@utastro.UUCP
Newsgroups: net.astro
Subject: StarDate: June 11 Where the Stars Don't Twinkle
Message-ID: <224@utastro.UUCP>
Date: Tue, 11-Jun-85 02:00:51 EDT
Article-I.D.: utastro.224
Posted: Tue Jun 11 02:00:51 1985
Date-Received: Thu, 13-Jun-85 23:41:09 EDT
Organization: U. Texas, Astronomy, Austin, TX
Lines: 34

When you're above Earth's atmosphere, the stars don't appear to
twinkle.  More -- in a minute.

June 11  Where the Stars Don't Twinkle

When we stand on the Earth, we see the universe of outer space while
looking through the blanket of Earth's atmosphere.  Looking through it
with powerful telescopes is a little like opening your eyes under water
-- things are a bit blurred.  The atmosphere also slightly dims the
light of the stars.  Stars look about 20% brighter to those working in
space -- say, in the orbit of the shuttle -- compared to what we see
down on the surface of our world, several hundred miles below.

So, once you get beyond the atmosphere, the stars look sharper and a
bit brighter -- and they don't appear to twinkle as they do from
Earth's surface.  Instead, stars seen from space all appear as
unwavering points of light.  The twinkling we notice from the ground
comes from the effect of the atmosphere on incoming waves of
starlight.  The atmosphere makes the light waves ripple -- incoming
waves from a single star interfere with each other as they descend
through Earth's blanket of air -- to our eyes.  This rippling produces
the brightness and color changes which we see as the twinkling of the
stars.

From an orbit around our Earth, the atmosphere also provides a
spectacular view of the brightest star -- and the closest one -- our
sun.  From the shuttle, while that craft moves in orbit around our
world, the astronauts watch as the sun moves out from behind the body
of the Earth every ninety minutes -- a brilliant diamond centered on
the backlighted crescent of the Earth's atmosphere.

Script by Diana Hadley, Harlan Smith and Deborah Byrd.

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