B1875.0

From Freepedia

The B1875.0 epoch is used in astronomy.

Since the right ascension and declination of stars are constantly changing due to precession, astronomers always specify these with reference to a particular epoch. The official constellation boundaries were defined in 1930 along the lines of right ascension and declination for this epoch.

The "B" in the prefix indicates that it is a Besselian epoch, as opposed to a Julian epoch. The 1875 figure refers to the year 1875 whose mean equator and equinox are used to define right ascension and declination of celestial bodies. See precession.