Re: ATM M-57 visibility

["Alan Levin" <ailevin@ix.netcom.com>]

Roger,

This topic was explored a few months ago in s.a.a.  In August Brian
Skiff posted that all published mag measurements are between
15.0-15.3 V, so it does not vary by much.  He explained that its
visibility is highly sensitive to seeing, and  reported multiple
observers seeing it in a 20cm telescope at 650x on a night of 
exceptional seeing!

You cannot simply calculate the limiting magnitude of a telescope based
on naked eye limits and geometry.   I have followed an AAVSO north
polar sequence down to 13.3 in a three inch telescope at 156x. 
A more experienced observer on the same night with the same telescope
was able to follow the sequence to 13.6.  Compared to a 7mm eyeball, the
3 inch has a 5.2 mag aperture advantage, and of course, I cannot see
down to 8.1 naked eye.

Magnification helps you see deeper into the sky.  I believe that Mel
Bartels has written a program to calculate the optimal magnification
to detect an object based on its size and brightness as well as the
background  brightness of the sky. 

Back to your original post,  I would not distrust Tommy's or Bob's 
observations based on your calculations alone.

Good Observing,
Alan