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Re: (meteorobs) Limiting Magnitude



On Sat, 29 Jan 2000 05:51:23 -0500 "Kim S. Youmans" <ksyo@pinelanddot net>
writes:
> Lew,
>   Actually, I thought I'd wind up putting my foot much farther down 
> my throat
> than I must have in my reply to Asaf!  I do indeed recall reading 
> that star
> counts should come from at or near zenith, but let disinformation 
> from another
> source overide what was only a vague recall.
>    The truth is, I'd rather use zenithal areas only for the exact 
> reasons you
> state...the ease in counting. Besides, if I can count areas at and 
> near zenith, I
> come up with higher LM's, which gives me a small motivational boost 
> to get out
> there and observe.  And I'm certainly glad you "called" me on it, 
> else I would
> have continued counting stars on the horizon!
>    But I must admit that haven't always counted three fields like I 
> should.
> During my first year out, I simply have not wanted the "work" to 
> spoil the
> "enjoyment," knowing that in time I'd be more familiar with all the 
> (usable)
> fields and their star patterns.
> Kim Youmans
> 
> Lew Gramer wrote:
> 
> > Kim Youmans posted a great reply to Asaf's questions on Limiting 
> Magnitude.
> > As Kim says, recording frequent LMs is one of the things which 
> distinguishes
> > a scientific amateur meteor observer from someone "just watching" 
> - without
> > the LM (and probably at least magnitude estimates for the meteors 
> you see),
> > people will have great difficulty making any scientific use of 
> what you saw.
> >
> > Your logs won't necessarily be "USELESS"! But the work needed to 
> render your
> > observation comparable to those of other observers around the 
> world, and the
> > inherent errors introduced by this kind of "compensation after the 
> fact",
> > make it really FAR less likely that you'll make a major 
> contribution...
> >
> > One gnit to gpick on Kim's reply, where he wrote:
> >
> > >A good observer will count at least three of these regions, one 
> near zenith,
> > >one at about 40-60 degrees up, and one near the horizon to get a 
> much better
> > >idea what his/her total LM really is.  After all, meteors appear 
> in any part
> > >of the sky, right? ...
> >
> > Actually, Kim this is exactly what I assumed when I started out - 
> but is not
> > what the IMO recommends... Reading carefully over the IMO page on 
> LMs at:
> >
> >     http://www.imodot net/visual/major01.html#sec52
> >
> > note that they define Limiting Magnitude as "the magnitude of the 
> faintest
> > star *near the zenith* that the observer can detect using slightly 
> averted
> > naked eye". And later on, they explicitly state that "The [LM 
> star] fields
> > should have an elevation of more than 40o".
> >
> > So in practice, for my own half-hourly LM star counts, I try to 
> use the two
> > (or three) LM fields which are closest to the Zenith, and that 
> DON'T require
> > me to move my body or crane my neck at all to count them. That 
> latter item
> > is key: I've often noted that even craning my neck 30 degrees can 
> really
> > reduce star counts due to distraction and lack of bloodflow to my 
> eyes (or
> > brain??), and can even cause what I call "strobing" - where 
> brighter areas
> > of my peripheral vision seem to "blink" brighter and fainter very 
> rapidly.
> >
> > [Does anyone else experience this "strobing", especially when 
> fatigued?]
> >
> > Clear skies and comfortable star counts everybody!
> > Lew
> >
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Lew:


	I was under the im-pression that it was a matter of " age " that created
my so called blinking. Now I must admit that this scenario is experienced
by others. I also have a nasty habit of " cranibg " my neck to aquire a
different view. Thanks for clearing this up.



								Sincerely

								Art Tello
								San Diego
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