OT: Asteroid transit

From: Matson, Robert (ROBERT.D.MATSON@saic.com)
Date: Tue Mar 20 2001 - 18:22:12 PST

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    Hi All,
    An off-topic tidbit to file away for later this year:  the
    Apollo asteroid (or is it an Aten?) 1999 MN is going to
    transit the sun on December 6th from around 8:20 to 11:50 UT.
    This is the only asteroid I've found which transits the
    sun as seen from earth this year.  Unfortunately, this tiny
    asteroid is far too small to be visible in silhouette, as it
    will be at a range of some 70 million miles.  Even if it
    were as large as a kilometer in diameter (which it isn't),
    it would only subtend 1.8 milliarcseconds.  (It's probably
    only a couple hundred meters across).
    So I guess the event falls into the category of "astronomical
    footnote".  A geometric curiosity, but not an observable one.
    With the inherent atmospheric limitations of ground-based
    telescopes, I wonder what the minimum detectable spot size
    would be for an instrument observing the sun?  The Big Bear
    Solar Observatory has a 26" reflector, and there are images
    on their website with pixel resolutions of 0.25 arcseconds
    (which means objects half this size could be easily detected).
    125 milliarcseconds corresponds to a 1-km asteroid at a range
    of 1.65 million km.
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