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      SUBROUTINE slH2E (AZ, EL, PHI, HA, DEC)

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      D E 2 H
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  Horizon to equatorial coordinates:  Az,El to HA,Dec

  (single precision)

  Given:
     AZ      r     azimuth
     EL      r     elevation
     PHI     r     observatory latitude

  Returned:
     HA      r     hour angle
     DEC     r     declination

  Notes:

  1)  All the arguments are angles in radians.

  2)  The sign convention for azimuth is north zero, east +pi/2.

  3)  HA is returned in the range +/-pi.  Declination is returned
      in the range +/-pi/2.

  4)  The latitude is (in principle) geodetic.  In critical
      applications, corrections for polar motion should be applied.

  5)  In some applications it will be important to specify the
      correct type of elevation in order to produce the required
      type of HA,Dec.  In particular, it may be important to
      distinguish between the elevation as affected by refraction,
      which will yield the "observed" HA,Dec, and the elevation
      in vacuo, which will yield the "topocentric" HA,Dec.  If the
      effects of diurnal aberration can be neglected, the
      topocentric HA,Dec may be used as an approximation to the
      "apparent" HA,Dec.

  6)  No range checking of arguments is done.

  7)  In applications which involve many such calculations, rather
      than calling the present routine it will be more efficient to
      use inline code, having previously computed fixed terms such
      as sine and cosine of latitude.

  P.T.Wallace   Starlink   21 February 1996

  Copyright (C) 1996 Rutherford Appleton Laboratory
  Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.

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