FreeLists / az-observing / [AZ-Observing] Re: How deep can you see?

[Brian Skiff <Brian.Skiff@xxxxxxxxxx>]

>>  so some lucky people can see naked-eye to mag 8 or below.

     One of the 'lucky' people (I do not think it is all that unusual,
in fact) is Bernie Sanden, by the way, who also spotted a mag. 8 star
in Coma without knowing of its presence beforehand.

>>  Does the eye work the same looking through a scope as opposed to
>>  naked-eye?

     Yes and no.  In the telescope you're usually working with exit pupils
rather smaller than the pupil of your eye (typically 1-3mm in the eyepiece
versus 5mm or more for your eye), so things like image sharpness and 
general acuity are less of a concern through the telescope, or there
are different physiological factors in play (darker backgrounds etc.).
That's why telescopic magnitude limits are a more consistent way of 
judging sky quality than naked-eye limits.

>> any ideas on a winter chart for this?

     I use (rather casually) fields near M31, in Coma, and in Hercules,
but know the only the one in Coma well.  There are these count-regions
used by meteor observers that are posted somewhere on the Web, and these
might be useful.  Another ploy is to use stars very close to the north
pole.  These are fix in elevation so you avoid problems with changing
atmospheric extinction, but are always relatively low (around 1.7 airmasses),
and near cities or whatever can be affected unlike the rest of the sky.
(By pole stars I mean within a couple degrees of the pole, _not_ the common
Little Dipper stars, which vary too much in height.)

     It helps in all of this to simply go out and practice it.  Several
times at the Texas Star Party, people who claimed not to be able to see
past mag. 6 (or even 5) could be readily led down to 7th by working with
them for 10 minutes on a particular spot of sky, and not telling them
until they had picked out several quite faint stars what their magnitudes
actually were.

\Brian
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