The B1875.0 epoch is used in astronomy. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... Astrometry: the study of the position of objects in the sky and their changes of position. ...

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. Right ascension (RA; symbol α: Greek letter alpha) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. ... In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. ... Jump to: navigation, search There are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail. ... Jump to: navigation, search 1930 is a common year starting on Wednesday. ...

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. A Besselian epoch, named after the German mathematician and astronomer Friedrich Bessel (1784 _ 1846), is an epoch that is based on a Besselian year, which is a tropical year measured at the point where the Suns longitude is exactly 280°. Since 1984, Besselian epochs have been superseded by... A Julian epoch is an epoch that is based on Julian years of exactly 365. ... 1875 was a common year starting on Friday (see link for calendar). ... Jump to: navigation, search There are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail. ...