- NAME
ZENPOS
- PURPOSE
Return the zenith RA and Dec for a given Julian date and observer longitude
and latitude
- CALLING SEQUENCE
ZENPOS, Date, Ra, Dec, [ Latitude= , Longitude = , /Degrees ]
- INPUT
Date The Julian date, in double precision, of the date and time
for which the zenith position is desired, scalar or vector.
- OPTIONAL INPUT KEYWORDS
LATITUDE - Latitude of the desired location (degrees)
LONGITUDE - Longitude of the desired location (degrees)
- OUTPUTS
RA - The right ascension of the zenith (in radians unless /Degrees is set)
Dec - The declination of the zenith (in radians unless /Degrees is set)
RA and Dec will have same number of elements as the input Julian date.
- 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 2 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
- COMMON BLOCKS
SITE - This common block should contain the scalars LAT, LNG
- PROCEDURE CALLS
CT2LST - Convert to Local Mean Sidereal Time
- MODIFICATION HISTORY
Written by Michael R. Greason, STX, 14 October 1988.
Update documentation, longitude now *east* of Greenwich W.L. July 2000
Add keywords for non-interactive use J. Sapp July 2016
Remove unneeded time zone info, add /Degrees W. Landsman Mar 2018