Out of interest down to what Mag is the entire sky reliably mapped?


The USNO B1 catalogue go to about mag 20 or 21, but I'd imagine that many
are missed at those levels, and the positions are apparently generally known
to a few tenths of an arcsecond.

The future GAIA satellite aims to provide sub-milliarcsecond accuracy in
positions for all stars to mag 20 (and accuracy of a few microarcseconds for
stars brighter than mag 15).