Besselian year. A quantity introduced by F. W. Bessel in the nineteenth century that has been used into the twentieth century.
Besselian year (NASA SP-7, 1965) = fictitious year. beta decay (NASA SP-7, 1965) Radioactive transformation of a nuclide in which the atomic number changes by ±1 with the emission of a beta particle and the mass number remains unchanged.
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. [S92] ...
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.
 See also: Orbit, Earth, Sun, Period, Revolution
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