Velocity component in a given direction due to Earth rotation.
R = sla_RVEROT (PHI, RA, DA, ST)
geodetic latitude of observing station (radians)
local apparent sidereal time (radians)
Component of Earth rotation in
direction RA,DA (km s-1)
Sign convention: the result is positive when the observatory
is receding from the given point on the sky.
Accuracy: the simple algorithm used assumes a spherical Earth and
an observing station at sea level; for actual observing
sites, the error is unlikely to be greater than 0.0005 km s-1.
For applications requiring greater precision, use the routine