(meteorobs) Naked-Eye Limiting Magnitude (non-IMO methods)
mameteors at yahoo.com
Fri Apr 8 12:55:44 EDT 2005
A couple of interesting pointers on determining naked-eye LMs via methods OTHER
THAN the IMO's standard star-count regions...
Here is a commercial product for determining LMs by "direct inspection" - i.e.,
knowing where stars of various faint mags. are, and "seeing if you can see
them." Actually an arguably suspect method for reliable estimates - but this
was widely used before the advent of IMO (e.g., by AMS observers):
Note again, these Duckek charts should NOT be used for IMO meteor recording.
However, for deep-sky observing reporting, they may be handy.
And here's a thread from the "[amastro]" advanced amateur astronomy group on
Yahoo! Again, I think these folks are discussing LMs determined by some variant
(possibly a double-blind version) of "direct inspection".
> Date: Fri, 08 Apr 2005 06:18:27 -0000
> From: "timokarhula" <...>
> Subject: NELM using glasses
> Hi folks! I wonder how faint stars those of you who use glasses (or
> lenses) have seen without (other) optical aid? A few tenths of a
> magnitude should be lost due to the lens surface. Has any near-sighted
> observer reached the 8th magnitude barrier naked eye (but using
> correcting lenses)?
> /Timo Karhula
> Date: Thu, 7 Apr 2005 23:29:39 -0700 (MST)
> From: Brian Skiff <...>
> Subject: Re: NELM using glasses
> I'm pretty sure Dave Nash, who saw down to 8.2 or so in observations
> we discussed here some months ago (most recently), wears glasses.
> I have seen to V=7.8 with patience with my approx -8 diopter correction.
> I'm pretty sure the light-loss from ordinary glass is only ~4 percent
> at each surface, so the difference should be much smaller than a
> few tenths of a magnitude---nominally only 0.08 mag for two air-to-glass
> In the coming months I'm planning to do some more of this sort of
> observing. I recently got a new set of glasses, and although not any
> stronger than before, we got the astigmatism correction better than
> in the past (my eyes have trefoil astigmatism, but of course the lens
> correction has just a single cylindrical component added). I also hope to
> take up the naked-eye-Neptune challenge, though it may be still too low
> in the sky and at too-low galactic latitude (i.e. bright background).
Lew Gramer <dedalus at alum.mit.edu>
Show us what our next emoticon should look like. Join the fun.
More information about the Meteorobs