These were intended as astrometric catalogs, not photometric. To quote from
"read.pht", the readme file on the USNO's website for the photometric data in
the USNO-A1.0 catalog:
-----------------------------------------
Summary:
The photometric calibration of USNO-A1.0 is about as poor as one can
have and still claim that the magnitudes mean something.
.....
--------------------------------------
-John
--- "G. G." <[EMAIL PROTECTED]> wrote:
> Often, I use catalogs USNO-A and USNO-B to identify faint stars.
> However, on many occasions these catalogs do not agree. Often, the
> difference is quite large (1+ magnitudes). Does anyone know which of
> these catalogs is more accurate?
>
> Thanks,
> Gennady
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