Besselian year
fictitious year

When using Besselian years, specify which definition is being used.

Besselian years, used mostly for star positions, can be encountered in older catalogs but are now becoming obsolete.

Since the switch to Julian years in the mid-1980s, it has become customary to prefix "B" to Besselian years.

A Besselian year is named after the German mathematician and astronomer Friedrich Bessel (1784-1846).

The Besselian year is a tropical year that starts when the (fictitious) mean Sun reaches an ecliptic longitude of 280 .

To distinguish between calendar years and Besselian years, it became customary to add ".0" to the Besselian years.

This astronomical notation is called Julian epoch and was introduced in 1984; before that time, astronomical year numbers with decimal fractions referred to Besselian years and were written without a letter prefix.

Meeus defines the beginning of a Besselian year to be the moment at which the mean longitude of the Sun, including the effect of aberration and measured from the mean equinox of the date, is exactly 280 degrees.

The definition depended on a particular theory of the orbit of the Earth around the Sun, that of Newcomb (1895), which is now obsolete; for that reason among others, the use of Besselian years has also become or is becoming obsolete.

The 49ers are accused of making undisclosed promises of payments to players and adding fictitious years to contracts.

(The fictitious year of birth, 1897, appears on his subsequent registration in the Navy Auxiliary Reserve and is widely given in both books and web sources.)