Name

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    HADEC2ALTAZ

Purpose

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      Converts Hour Angle and Declination to Horizon (alt-az) coordinates.

Explanation

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      Can deal with NCP/SCP singularity. Intended mainly to be used by
      program EQ2HOR

Calling Sequence

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      HADEC2ALTAZ, ha, dec, lat ,alt ,az [ /WS ]

Inputs

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    ha - the local apparent hour angle, in DEGREES, scalar or vector
    dec - the local apparent declination, in DEGREES, scalar or vector
    lat - the local latitude, in DEGREES, scalar or vector

Outputs

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    alt - the local apparent altitude, in DEGREES.
    az - the local apparent azimuth, in DEGREES, all results in double
          precision

Optional Keyword Input

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      /WS - Set this keyword for the output azimuth to be measured West from
            South. The default is to measure azimuth East from North.

Example

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    What were the apparent altitude and azimuth of the sun when it transited
    the local meridian at Pine Bluff Observatory (Lat=+43.07833 degrees) on
    April 21, 2002? An object transits the local meridian at 0 hour angle.
    Assume this will happen at roughly 1 PM local time (18:00 UTC).
    IDL> jdcnv, 2002, 4, 21, 18., jd ; get rough Julian date to determine
                                      ;Sun ra, dec.
    IDL> sunpos, jd, ra, dec
    IDL> hadec2altaz, 0., dec, 43.078333, alt, az
      ===> Altitude alt = 58.90
            Azimuth az = 180.0

Revision History

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