Hi Jonathan, > But what is the point in making a geosat synchronous with the stars? > It's not going to stay over an area of Earth (more or less). What > is the purpose for a geosat to track the stars? Perhaps I can explain. You need to forget about the sun for the moment since it doesn't have anything to do with the earth's rotation rate. Just pretend it isn't there. The only thing that matters is how long it takes the earth to complete one revolution on its axis in an inertial reference frame. The answer is 23h 56m and some odd seconds. Since this is the earth rotation rate, this is the value that must be matched by the satellite. In effect, 24 hours is the average time that it takes the sun to "complete one apparent orbit" around the earth. Thus the sun is "out of synch" with the GEO satellite to the tune of about 4 minutes per day. Now if you measure time with a sidereal clock, you'll see that geosynchronous satellites (with zero inclination), always return to the same RA/Dec at the same sidereal time each night. Best, Rob ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
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