Thank you all for your answers! Your comments fit to that I heard respectively thought of.
GSC indeed has a lot of artefacts, we do not do much astrometry. Here is a link to the observatory I watch the skies with three friends, but I am not the owner; it is a superb instrument: http://www.harpoint-observatory.com/ Greetings and clear skies to you, Michael --- In [email protected], John Mahony <jmmah...@...> wrote: > > It's hard to directly compare two catalogs since they may have been made for > different purposes. Most of the deep catalogs are for precise astrometry > (position), while some catalogs are for precise photometry (brightness). > > Neither of these will matter for most amateur use, unless you do some "real > science" with your scope. If you just want a deeper catalog, then yes, UCAC3 > goes more than a magnitude deeper than GSC and has about 5 times as many > stars. > > Your question about whether "UCAC3 catalog replaces HST GSC catalog because > of the more precise magnitudes of UCAC3 (the limiting magnitude is fainter > with ~m16.5 anyway)" is hard to answer. Both of these catalogs were made > for astrometry, and just because a catalog goes fainter doesn't mean it's > more precise, especially if you're talking about using an astrometric catalog > for photometry. For a blatant example, see the astrometric catalog > USNO-A1.0, the first "very deep" catalog showing most of the stars in the > Palomar Schmidt all-sky survey plates, which goes much fainter (with half a > billion stars to about mag 20, compared to about 20 million stars to mag 15, > for GSC, or 100 million to mag 16.5 for UCAC3) than any of these catalogs, > but where the developer admitted that "The photometric calibration of > USNO-A1.0 is about as poor as one can have and still claim that the > magnitudes mean something". When you go very deep, there aren't many > references > to use for calibration. Or to use a completely different analogy, the early > maps of the "new world" made by Columbus and other early European explorers > went much "further" than any earlier map, but weren't very accurate. > > -John > > > > > ----- Original Message ---- > > From: babarosa6 <babar...@...> > > To: [email protected] > > Sent: Sun, October 4, 2009 3:44:05 PM > > Subject: [skychart-discussion] UCAC3 versus HST GSC > > > > Hi! > > > > I have a (maybe sheepish) question: > > > > Am I right that UCAC3 catalog replaces HST GSC catalog because of the more > > precise magnitudes of UCAC3 (the limiting magnitude is fainter with ~m16.5 > > anyway)? > > > > Installing and using it with skychart_3.1-1232_i386.deb works fine. > > > > Greetings > > Michael > > > > > > > > ------------------------------------ > > > > Yahoo! Groups Links > > > > > > >
