on 12/20/01 10:26 AM, Peter Natscher at natscher@No-Spam wrote:
> I'm finding in my cross references on galaxies to be obseved that there are
> notable differences in magnitude assignments of specific galaxies I plan to
> observe. This includes the references of SA2000, The Sky, and Uranometria
> which I use. Some magnitude designations per galaxy differ by 2 mags. So, in
> looking for new galaxies, I've been surprised in what to expect for their
> visibility level--some were brighter than expected while others which I
> thought I could see were not there at all.
Most of the magnitudes from older sources (except for the brighter stuff)
were based on photographic (blue-sensitive) plates in the late '50's and
'60's and are not visual magnitudes. As a general rule, these are roughly a
magnitude fainter than a true V magnitude. To further muck up the
situation, many of the fainter magnitudes came are very rough --
particularly those from as the MCG (Morphological Catalogue of Galaxies) and
can be off by two magnitudes!
Still, these older photographic magnitudes (generally based on the POSS)
were "modified" slightly to convert to a standard B magnitude and are given
in the PGC. Unfortunately, the PGC is the catalogue source for many of the
popular charting software such as TheSky and MegaStar! Some of the recent
lists (such as my Orion DeepMap and the new Deep Sky Field Guide) give
visual magnitudes, so these will differ quite a bit as you noted from
TheSky!
Steve Gottlieb
This archive was generated by hypermail 2b29 : Thu Dec 20 2001 - 15:12:04 MST