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REAL FUNCTION sla_RVEROT (PHI, RA, DA, ST)
*+
* - - - - - - -
* R V E R O T
* - - - - - - -
*
* Velocity component in a given direction due to Earth rotation
* (single precision)
*
* Given:
* PHI real latitude of observing station (geodetic)
* RA,DA real apparent RA,DEC
* ST real local apparent sidereal time
*
* PHI, RA, DEC and ST are all in radians.
*
* Result:
* Component of Earth rotation in direction RA,DA (km/s)
*
* Sign convention:
* The result is +ve when the observatory is receding from the
* given point on the sky.
*
* Accuracy:
* The simple algorithm used assumes a spherical Earth, of
* a radius chosen to give results accurate to about 0.0005 km/s
* for observing stations at typical latitudes and heights. For
* applications requiring greater precision, use the routine
* sla_PVOBS.
*
* P.T.Wallace Starlink 20 July 1994
*
* Copyright (C) 1995 Rutherford Appleton Laboratory
*-
IMPLICIT NONE
REAL PHI,RA,DA,ST
* Nominal mean sidereal speed of Earth equator in km/s (the actual
* value is about 0.4651)
REAL ESPEED
PARAMETER (ESPEED=0.4655)
sla_RVEROT=ESPEED*COS(PHI)*SIN(ST-RA)*COS(DA)
END
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