Path: utzoo!mnetor!uunet!lll-winken!lll-lcc!ames!pasteur!ucbvax!hplabs!hpda!hpwala!dalec
From: dalec@hpwala.HP.COM (Dale Coder)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Celestial Navigation
Message-ID: <305@hpwala.HP.COM>
Date: 26 Feb 88 15:16:47 GMT
Organization: Hewlett Packard, Waltham, Mass
Lines: 33


	What you want to do is easy in terms of computing power but
difficult in terms of data entry. What you need to do is develop
equations to perform three dimensional transformations on objects.
These will take the viewer's position and orientation, along
with the position of the celestial objects, and give you the
objects' position relative to the viewer. You can find these equations
in any text on computer graphics ("An Introduction to Interactive Computer
Graphics" is a good one).

	However, you first need to enter the positions of the stars
in absolute (galactic) coordinates. If you want to do all of the
stars you are in for a lot of typing (there are approximately one
hundred billion in our galaxy alone). Planets are easier. Although
there is great evidence to suggest the existence of planets circling
stars other than our own, there is no definite proof yet--our detection
equipment isn't that good. Therefore there are only nine planets known:
those in our own solar system.

	Of course, you may want to take into account the movement of
the stars. The stars of our galaxy revolve around the galactic center
once every 250 million years. (Personally, I wouldn't bother with worrying
about star movement). In the case of the planets, the period of revolution
is much shorter so you probably should worry about it.

	As for ascertaining what these positions are, I'm sure the
astronomy department library of your local university should help.
The positions of most of the major stars have been plotted using either
the parallax or redshift method.

	By the way, isn't there an astronomy newsgroup you can post 
enquiries to?

				Dale Coder