ee00(jdtt, epsa, dpsi)
[SOFA] Returns the equation of the equinoxes (IAU 2000) given the TT
jdtt, the mean obliquity
(radians, mean of date), and the nutation in longitude
epsa (in radians). All three parameters must have the
same dimensions. The returned value has those same dimensions, too,
and is measured in radians.
Greenwich apparent sidereal time (gast) is equal to Greenwish mean sidereal time (gmst) plus the equation of the equinoxes.
See also: Astronomical Coordinate Calculations