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      REAL FUNCTION slRVER (PHI, RA, DA, ST)

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      R V E R
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  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
     slPVOB.

  P.T.Wallace   Starlink   20 July 1994

  Copyright (C) 1995 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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