From Friedrich Wilhelm Bessel (1784-1846), German astronomer and mathematicians, who made fundamental contributions to positional and spherical astronomy.
Fr.: équation de Bessel
A linear second-order differential equation, the solutions to which are called Bessel functions.
Hamugeš, → equation.
Fr.: étoile de Bessel
Same as → 61 Cygni, the first star whose distance was measured, by Friedrich Bessel in 1838.
Fr.: besselien, de Bessel
Of or pertaining to Friedrich Wilhelm Bessel (1784-1846) or to his discoveries. → Besselian day number → → Bessel equation → Besselian star constant → → Besselian year.
Besselian day number
šomâre-ye ruz-e Besseli
Any of the five quantities denoted by A, B, C, D, and E used in conjunction with → Besselian star constants for the reduction of a star's → mean catalog place to its → apparent place.
Besselian star constant
pâyâ-ye axtari-ye Besseli
Fr.: constante stellaire besselienne
Any of the eight quantities denoted by a, b, c, d (for → right ascension) and a', b', c', d' (for → declination) used in conjunction with → Besselian day numbers for the reduction of star's → mean catalog place.
Fr.: année besselienne
The period taken for the right ascension of the mean Sun to increase by 24 hours. The starting point is when the mean Sun's longitude is 280°, corresponding roughly to January 1. It is virtually the same as the tropical year.