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Re: (meteorobs) Hale/Bopp Observation Jan 29 ZAYGE



Wesley, I think you are probably correct about low elevation atmospheric 
effects making a difference in estimates. Last night was particularly clear 
and cloud free, and I saw it right about at Astronomical twilight.
My previous look was thru not as clear skies, with the comet a week lower 
(5 to 10 degrees) and during the period between Astro and Nautical 
twilight...all adverse effects. Gee I'll just have to get up every clear 
morning and look! :->

Wayne
-------------
Original Text
From: Wesley Stone <wstone@lclarkdot edu>, on 1/29/97 3:12 PM:
To: <meteorobs@latrade.com>

On Wed, 29 Jan 1997 wayne.t.hally@bangate1.tek.com wrote:

> Interesting.
> I thought it was much brighter than my last look 9 days ago. Naked eye I 
> judged it the same mag (approx) as the star above Altair, and the one at 
> the (currently) upper wing tip (2 corner starts of LM area 5). I don't 
know 
> which greek letters they are as I have no references with me...I'll check 
> tomorrow
> 
> Wayne
> -------------
> Original Text
> 
My estimate for
> >Hale/Bopps magnitude is between 2.7 and 2.9. I believe this is pretty 
> close
> >to what I saw during my last sighting on Jan 20? I get the impression 
that
> >it's stuck on this magnitude range for the moment.

So it seems to go with estimating comet magnitudes.  I think Gamma Aql 
(just above Altair) comes in at 2.7.  My personal observations have shown 
up to a 0.5 magnitude flux with no distinct trend.  I think this is 
mostly due to differences in local atmospheric conditions (haze, etc.) 
over the dates.  Unlike Hyakutake last year, which jumped noticeably each 
night in March, Hale-Bopp's rise to prominence will be rather slow, with 
an average 0.1 magnitude rise over every two to three days.  Variations 
even greater than this may be difficult to pick out.  An added factor is 
Hale-Bopp's low altitude.  Some people have been correcting for 
differential extinction, which just adds another source of uncertainty to 
an already uncertain estimate (sorta like ZHR corrections).  These 
magnitude estimates (or those from the most "reliable" observers) are 
used to make predictions of the comet's brightening trend, which is 
itself variable.  It's quite fascinating.  The best page on this subject 
is Charles Morris's at http://encke.jpl.nasadot gov/  .  Go to "Follow the 
Comet's Changing Brightness".  It's fun to play around with the numbers.  
Even if the current magnitude estimates are overestimates and the comet 
stops showing any sign of cometary activity, it should still reach 
magnitude 1.5 (hopefully it will do much better than that, but...).

There is also an article in Sky and Telescope from April, 1974 (read: 
just post-Kohoutek) that also discusses brightness predictions (but not
estimates) and cometary behavior and chronicles a couple of real flops
that were promising at first but completely disintegrated on their way to
perihelion.  (Jacchia, Luigi G.  "The Brightness of Comets." Sky and 
Telescope, April 1974, p.218-220.)