Re: flaring geo sat video on spaceweather

From: Björn Gimle (bjorn.gimle@gmail.com)
Date: Fri Apr 15 2011 - 09:51:13 UTC

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    My guess is:
    The shadow cone is almost fixed in RA during a night, compared to Earth
    rotation.
    To be able to photograph the shadow entry, the camera must move westward.
    So the camera ought to move with the stars, 15 deg/h !
    The parallax of rotation increases the azimuthal speed, at Swiss latitudes
    by about 10% higher at midnight .
    
    You can see the stars rising almost vertically, which they don't do in
    Switzerland.
    So it appears the photographer has choosen a compromise to retain the
    references to terrestrial objects in the E-SE.
    
    /Björn
    
    2011/4/15 Greg Roberts <grr@telkomsa.net>
    
    > Morning George -
    >
    > As you say a most spectacular representation of what happens.
    >
    > However I may be being a little dense this morning but something puzzles
    > me.
    >
    > The camera is not tracking at sidereal rate so the stars cross the field of
    > view left to right. Since the target is geostationary satellites these will
    > remain more or less fixed in the centre of the field. All okay so far.
    >
    > But what puzzles me is why what appears to be fixed horizon objects are
    > moving - a geo ,for most practical purposes is at a fixed az/el, neglecting
    > the objects inclination at this image scale so I would expect the horizon
    > to
    > be static and some small variation in the geosats image,but instead there
    > is
    > considerable horizon movement. Using VLC I slowed the image down to 0.06
    > times its normal speed - can see the leos crossing the field much more
    > clearly etc.
    >
    > As I said earlier I may be being dense this morning- a not unusual event !
    >
    > Cheers
    > Greg
    >
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    >
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