fictitious year

(astronomy) The period between successive returns of the fictitious mean sun to a sidereal hour angle of 80° (right ascension 18 hours 40 minutes; about January 1); 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. Also known as Besselian year.

[Etymology: F. W. Bessel; Germany 1784-1846] astronomy Now the Julian year, i.e. 365.25 days, = ¹/₁₀₀ Julian century of 36 525 days.

Originally the year of a calendar scheme established by Bessel, the year beginning when the mean Sun reaches 18 h 40 min of right ascension (which currently occurs on 1 January). Variablity of the length of the year (which is essentially that of the tropical year but more varied because of being demarcated close to a solstice), and having its calendar offset from the noon moment that demarcates the Julian day number, led to the practical demise of this pioneer scheme for identifying astronomical epochs. Being based on a fictitious Sun, the Besselian year was also called the annus fictus or fictitious year
[McGraw-Hill Dictionary of Scientific and Technical Terms, 5th edn (New York, McGraw-Hill, 1994)] and, ambiguously, because of other meanings for the name, the astronomical year.