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ALTAZ2HADEC

ALTAZ2HADEC

Name


    ALTAZ2HADEC

Purpose


    Convert Horizon (Alt-Az) coordinates to Hour Angle and Declination.

Explanation


    Can deal with the NCP singularity. Intended mainly to be used by
    program hor2eq.pro

Calling Sequence


  ALTAZ2HADEC, alt, az, lat, ha, dec

Inputs


  alt - the local apparent altitude, in DEGREES, scalar or vector
  az - the local apparent azimuth, in DEGREES, scalar or vector,
        measured EAST of NORTH!!! If you have measured azimuth west-of-south
        (like the book MEEUS does), convert it to east of north via:
                      az = (az + 180) mod 360
  lat - the local geodetic latitude, in DEGREES, scalar or vector.

Outputs


  ha - the local apparent hour angle, in DEGREES. The hour angle is the
          time that right ascension of 0 hours crosses the local meridian.
          It is unambiguously defined.
  dec - the local apparent declination, in DEGREES.

Example


    Arcturus is observed at an apparent altitude of 59d,05m,10s and an
    azimuth (measured east of north) of 133d,18m,29s while at the
    latitude of +43.07833 degrees.
    What are the local hour angle and declination of this object?
    IDL> altaz2hadec, ten(59,05,10), ten(133,18,29), 43.07833, ha, dec
    ===> Hour angle ha = 336.683 degrees
          Declination, dec = 19.1824 degrees
      The widely available XEPHEM code gets:
                Hour Angle = 336.683
                Declination = 19.1824

Revision History


    Written Chris O'Dell Univ. of Wisconsin-Madison May 2002



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