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.help zd Jun99 "Slalib Package"
.nf
DOUBLE PRECISION FUNCTION slZD (HA, DEC, PHI)
- - -
Z D
- - -
HA, Dec to Zenith Distance (double precision)
Given:
HA d Hour Angle in radians
DEC d declination in radians
PHI d observatory latitude in radians
The result is in the range 0 to pi.
Notes:
1) The latitude must be geodetic. In critical applications,
corrections for polar motion should be applied.
2) In some applications it will be important to specify the
correct type of hour angle and declination in order to
produce the required type of zenith distance. In particular,
it may be important to distinguish between the zenith distance
as affected by refraction, which would require the "observed"
HA,Dec, and the zenith distance in vacuo, which would require
the "topocentric" HA,Dec. If the effects of diurnal aberration
can be neglected, the "apparent" HA,Dec may be used instead of
the topocentric HA,Dec.
3) No range checking of arguments is done.
4) In applications which involve many zenith distance calculations,
rather than calling the present routine it will be more efficient
to use inline code, having previously computed fixed terms such
as sine and cosine of latitude, and perhaps sine and cosine of
declination.
P.T.Wallace Starlink 3 April 1994
Copyright (C) 1995 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
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.endhelp
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