Date: Sun Mar 13 2011 - 20:59:33 UTC

  • Next message: George Kristiansen: "RE: DIY Predictions?"

     The "speed" of the stars is not the issue - they move only because of 
     Earth rotation.
     But the Earth's surface moves at up to .463 km/s (equator) and a 
     typical LEO at 7.5 km/s - a ratio of only 1:16
     A higher satellite is slower (physically), put the rotation speed of a 
     point above a fixed longitude at e.g. 12000 km altitude is 1.33 km/s, so 
     there is a drastic influence, if the satellite is not moving straight 
     Rob Matson's SkyMap allows you to plot either the true motion among 
     stars or the apparent alt-az motion. I have combined the pairs for an 
     Iridium and a MEO satellite. I made the alt-az tracks red, the RA-Dec 
     tracks blue.
     /Björn Gimle
    >A typical field of view is 1 degree. It would take 4 minutes for stars 
    > to
    >cross from one side to the other. A typical LEO would take 1 second.
    >Your field of view may be larger but the point is the ratio of 
    > velocities is
    >about 300 to 1. Even if the LEO is perpendicular the arctangent of 
    > 1/300 is
    >.2 degrees. Probably too small to measure.
    >You need a satellite much higher that takes more like 1 minute to 
    > cross the
    >field of view. Of course these are very faint.
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