Name

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    ALTAZ2HADEC

Purpose

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

Explanation

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

Calling Sequence

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  ALTAZ2HADEC, alt, az, lat, ha, dec

Inputs

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  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

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  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

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    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

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