NV5 GEOSPATIAL SOFTWARE
>  Docs Center  >  Libraries  >  ASTROLIB  >  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

© NV5 Geospatial Solutions, Inc. |  Legal