[SOFA] Returns the equation of the origins measured in radians, using
the IAU 2006 precession and IAU 2000A nutation models, for the given
TT Julian Dates
jdtt. The returned value has the same
dimensions as the parameter.
The equation of the origins is the distance between the true equinox and the celestial intermediate origin, or, equivalently, between the Earth rotation angle and Greenwich apparent sidereal time. It is equal to the precession in right ascension since J2000.0 plus the equation of the equinoxes including the small correction terms.
See also: Astronomical Coordinate Calculations