15.5.297 gst00a

gst00a(jdut, jdtt)

[SOFA] Returns Greenwich apparent sidereal time in radians consistent with IAU 2000 resolutions. jdut is the Julian Date (UT1). jdtt is the Julian Date (TT) of the same instant. jdut is needed to predict the Earth rotation, and TT to predict the effects of precession. If jdtt is set equal to jdut then errors of order 100 microarcseconds result. Both parameters must have the same dimensions, and the result has those same dimensions, too.

See also: Astronomical Coordinate Calculations