- NAME
ZENPOS
- PURPOSE
Return the zenith RA and Dec in radians for a given Julian date.
- CALLING SEQUENCE
ZENPOS, Date, Ra, Dec
- INPUT
Date The Julian date, in double precision, of the date and time
for which the zenith position is desired, scalar or vector.
- OPTIONAL INPUTS
LATITUDE Latitude of the desired location.
LONGITUDE Longitude of the desired location.
TZ Time zone (see below).
- OUTPUTS
Ra The right ascension in RADIANS of the zenith.
Dec The declination in RADIANS of the zenith.
- PROCEDURE
The local sidereal time is computed; this is the RA of the zenith.
It and the observatories latitude (corresponding to the Dec.) are
converted to radians and returned as the zenith direction.
- PROMPTS
ZENPOS will prompt for the following 3 parameters if they are not
defined in the common block SITE (see below) or provided as
keywords. Keywords override information in the common block.
LAT,LNG - north latitude and east longitude of the desired location
in DEGREES
TZONE - Time Zone (in hours) of the desired location (e.g. 4 = EDT,
5 = EST)
- COMMON BLOCKS
SITE - This common block should contain the three scalars LAT, LNG
and TZONE
- PROCEDURE CALLS
CT2LST - Convert to Local Mean Sidereal Time
- MODIFICATION HISTORY
Written by Michael R. Greason, STX, 14 October 1988.
Converted to IDL V5.0 W. Landsman September 1997
Update documentation, longitude now *east* of Greenwich W.L. July 2000
Add keywords for non-interactive use J. Sapp July 2016