Re: Solar/lunar transits

From: Allen Thomson (
Date: Fri Jan 26 2001 - 13:53:29 PST

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    Robert Matson replied to Bruno Tilgner
    > Hi Bruno,
    > > Even satellites in low earth orbit, which would be at a distance of 1000
    > > to 2000 km from the observer, cannot be seen because the image would
    > > be wiped out by atmospheric turbulence.
    > Perhaps at 2000 km range, but at 1000 km a 10-meter
    > object subtends 2 arcseconds.  This is within the
    > realm of possibility.  And with a larger satellite like
    > Mir, ISS or the Shuttle (where the range can also be
    > quite a bit less than 1000 km), observation should be
    > no problem at all.
         In addition, the extreme brightness of the solar disk should make
    short-exposure imaging fairly easy, thus offering the possibility of evading
    turbulence-caused seeing effects.  Granted, the short duration of the
    transit would limit the number of exposures taken during any one session,
    but it would be worth trying.  A morning transit, before solar heating had
    stirred up the surface layers of air, or a site like Big Bear Lake
    ( would give the best chance.   Morning transit
    would imply, of course, greater range and less linear resolution -- probably
    a coastal site with ocean or large lake to the east would be best, as that
    would extend the low-turbulence period later into the day.
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