Re: Sidereal Tracking vs Fixed Scope

From: George Roberts (
Date: Sun Mar 13 2011 - 15:48:49 UTC

  • Next message: Giuseppe N. Gerbore: "DIY Predictions?"

    >thinking of obtaining a broken trace.
    "bent" is a better word here than "broken".
    >Either my reasoning is wrong or the effect is so small as to be 
    Yes, undetectable.
    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.
    - George Roberts
    -----Original Message----- 
    From: Giuseppe N. Gerbore
    Sent: Sunday, March 13, 2011 11:10 AM
    Subject: Sidereal Tracking vs Fixed Scope
    Bad weather, no obs possible, let's revert to theory.
    We are capturing a LEO satellite on a CCD. There are two setups:
    1) Mount tracking stars in sidereal mode
    2) Mount still
    The trace on CCD should have a different slope, because in case 1 what we 
    obtain is the resultant of Earth velocity vector and Sat velocity vector.
    Not being able to capture with two simultaneous setups on the same satellite 
    I stop tracking in the middle of the FOV,
    See this image to understand what I mean.
    As far as now I could not prove the above.
    Either my reasoning is wrong or the effect is so small as to be 
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