Greenwich mean sideral time (IERS 1996)
[gmst,[gmstp]]=CL_mod_sidTime(cjd_ut1)
Computes the Greenwich mean sideral time gmst (IERS standard 1996).
It also optionally computes the first derivative of the sideral time : gmstp. (this value is not a constant)
Modified (1950.0) Julian day, in UT1 time scale (1xN)
Greenwich mean sideral time [rad]
Greenwich mean sideral time first derivative [rad/s]
CNES - DCT/SB
1) IERS Conventions (1996), Dennis D. McCarthy