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(meteorobs) Fwd Re: Imaging comet tails?


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Date: Wed, 26 Aug 1998 12:37:06 -0700
From: bas@lowell.Lowelldot edu (Brian Skiff)
To: dedalus@latrade.com
Subject: Re: Imaging comet tails?
Cc: mplist@bitnik.com

     About the faintest you can go from the ground without extraordinary
means is a surface brightness of around mag. 27 per square arcsecond.
     The geometry of comet tails, at least ones assumed to be straight,
means that the tails cannot appear longer than the phase angle of the
comet.  There were several reports by nominally reputable observers during
the Hyakutake apparition indicating tail lengths much longer than this---
they were erroneous, probably caused by strings of faint (mag 7-8) stars
in the region concerned, and possibly by some over-enthusiasm.  This limit
applies even if the tail is infinitely long.  If the tail is curved, then
obviously if the geometry is right, then it can appear longer.  This wasn't
the case for Hyakutake:  the tail we saw wasn't intrinsically very long
because the comet was so close to Earth (it was also an intrinsically faint
comet, bright only because of its proximity).

\Brian

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