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`gst00a(`

`jdut`, `jdtt`)

[SOFA] Returns Greenwich apparent sidereal time in radians consistent
with IAU 2000 resolutions.

is the Julian Date
(UT1). `jdut`

is the Julian Date (TT) of the same
instant. `jdtt`

is needed to predict the Earth rotation,
and TT to predict the effects of precession. If `jdut`

is
set equal to `jdtt`

then errors of order 100
microarcseconds result. Both parameters must have the same
dimensions, and the result has those same dimensions, too.
`jdut`

See also: Astronomical Coordinate Calculations