[vsnet-chat 1376] comparison of GSPC and USNO-based V mags

[aah@nofs.navy.mil]

While Taichi Kato's comparison between my variable star field photometry and USNO-A1.0 is
quite interesting, I think it would be even more interesting if he compared against
USNO-A2.0, since that is the catalog where the photometry is supposedly somewhat better.
Beware of any star in my photometry with V fainter than 18.5 or so...my exposures were
not long enough to give better than 0.1mag precision at this magnitude.

Also, I will reiterate once again.  Dave never promised identical star numbers on
subsequent releases, and that is definitely true between USNOA-1.0 and USNOA-2.0.  There
are many millions of 'new' stars (better astrometry has enabled the retention of some
stars that were missed before), and the index into each of the zone files is different.

Arne

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