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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
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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.)