C+
C NAME:
C	Time2GST
C PURPOSE:
C	Calculate Greenwich Sidereal Time.
C	Good for years 1901 through 2099. Accuracy is 0.006 degree.
C CATEGORY:
C	Celestial mechanics
C CALLING SEQUENCE:
	double precision function Time2GST(tt)
C INPUTS:
C	tt(2)		integer			time
C OUTPUTS:
C	Time2TGST	double precision	Greenwich sidereal time (degrees)
C CALLS:
C	Time2YDoy, Time2Day8
C RESTRICTIONS:
C	Only valid for years 1901 through 2099
C PROCEDURE:
C	Local Sidereal Time	= Hour Angle of the vernal equinox
C				= Right Ascension of zenith
C	For star X : RA(X)+HA(X)=LST
C MODIFICATION HISTORY:
C	Extracted from:
C	Geophysical Coordinate Transformations, C.T. Russell, in:
C		Cosmic Electrodynamics 2 (1971) 184-196
C-
	    integer		tt(2)

	integer			yr
	integer			doy(2)
	integer			day

	double precision	d
	double precision	f

	call Time2YDoy(0,tt,yr,doy)
	day = doy(1)
	doy(1) = 0
	call Time2Day8(0,doy,f)

	d = 365*(yr-1900)+(yr-1901)/4+day+f-0.5d0
	Time2GST = dmod(279.690983d0+0.9856473354d0*d+360.0d0*f+180.0d0,360.0d0)

	return
	end