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From: eder@ssc-vax.UUCP (Dani Eder)
Newsgroups: net.movies.sw
Subject: Re: 'Parsec' as a unit of time - (nf)
Message-ID: <672@ssc-vax.UUCP>
Date: Mon, 12-Dec-83 12:13:51 EST
Article-I.D.: ssc-vax.672
Posted: Mon Dec 12 12:13:51 1983
Date-Received: Wed, 14-Dec-83 02:09:26 EST
References: <123@tpvax.fluke.UUCP>
Organization: Boeing Aerospace, Seattle
Lines: 16


                                                12 December 1983

     The parsec is not a universal constant, it depends on the size of
the Earth's orbit.  Parallax is the apparent motion of nearby stars
relative to much further background stars caused by the Earth's motion
around the Sun.  A parallax of one arc second is caused when the size
of the Earth's orbit as seen from the star in question is one second
of arc wide.  This implies that a parsec is 206264.8 times the diamter
of a planet's orbit, whatever that diameter is.  The constant, by the
way, is the number of seconds of arc in one radian.

                                                 Dani Eder
                                                 Boeing Aerospace
                                                 ssc-vax!eder