Besselian year

Also called Besselian year, Bessel fictitious year. The length of the fictitious year is the same as that of the tropical year, since both are based upon the position of the sun with respect to the vernal equinox.

The beginning of a Besselian year, traditionally used as as standard epoch, is denoted by the suffix ".0". Since 1984 standard epochs have been defined by the Julian year rather that the Besselian year.

0 - the mean equator and equinox of 1949 December 31st 22:09 UT, the "B" meaning Besselian year, the fictitious solar year introduced by F. W. Bessell in the nineteenth century.

Prior to 1984 coordinates of star catalogs were commonly referred to the mean equator and equinox of the beginning of a Besselian year. Beginning with 1984 the Julian year has been used, as denoted by the prefix J, e.g., J2000.0.

A Besselian epoch, named after the German mathematician and astronomer Friedrich Bessel (1784 â€" 1846), is an epoch that is based on a Besselian year of 365.

The period between successive returns of the sun to a sidereal hour angle of 80 degrees is called a fictitious or Besselian year. A civil year is the calendar year of 365 days in common years, or 366 days in leap years.

See also: Sun, Orbit, Earth, Year, Element