Quote:
Originally Posted by pgc hunter
Which one is the actual visual magnitude?
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Strictly speaking, neither, as they are both determined photometrically and there
is a bit of hocus pocus that goes on in deriving them.
However, the V (V_T) value will often give a rough estimation of the
visual magnitude for some objects.
At the very least, it is always wise to consider surface brightness estimates in
conjunction with integrated magnitude estimates when trying to determine whether
an extended object will be visible through the eyepiece.
Over the years, various practitioners have attempted to hammer the photometric
data from various sky surveys into visual estimates with mixed success. Several
formulae have been proposed but most eventually fail in their modeling at some point.
Historically, many of the surveys were done on emulsion plates with a bias of sensitivity
to the blue, which is one of the many factors that various attempts to massage the data
have had to contend with.
Nothing beats eyeballing the object in the end.
Best Regards
Gary
