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.help altaz Jun99 "Slalib Package"
.nf
SUBROUTINE slALAZ (HA, DEC, PHI,
: AZ, AZD, AZDD, EL, ELD, ELDD, PA, PAD, PADD)
- - - - - -
A L A Z
- - - - - -
Positions, velocities and accelerations for an altazimuth
telescope mount.
(double precision)
Given:
HA d hour angle
DEC d declination
PHI d observatory latitude
Returned:
AZ d azimuth
AZD d " velocity
AZDD d " acceleration
EL d elevation
ELD d " velocity
ELDD d " acceleration
PA d parallactic angle
PAD d " " velocity
PADD d " " acceleration
Notes:
1) Natural units are used throughout. HA, DEC, PHI, AZ, EL
and ZD are in radians. The velocities and accelerations
assume constant declination and constant rate of change of
hour angle (as for tracking a star); the units of AZD, ELD
and PAD are radians per radian of HA, while the units of AZDD,
ELDD and PADD are radians per radian of HA squared. To
convert into practical degree- and second-based units:
angles * 360/2pi -> degrees
velocities * (2pi/86400)*(360/2pi) -> degree/sec
accelerations * ((2pi/86400)**2)*(360/2pi) -> degree/sec/sec
Note that the seconds here are sidereal rather than SI. One
sidereal second is about 0.99727 SI seconds.
The velocity and acceleration factors assume the sidereal
tracking case. Their respective numerical values are (exactly)
1/240 and (approximately) 1/3300236.9.
2) Azimuth is returned in the range 0-2pi; north is zero,
and east is +pi/2. Elevation and parallactic angle are
returned in the range +/-pi/2. Position angle is +ve
for a star west of the meridian and is the angle NP-star-zenith.
3) The latitude is geodetic as opposed to geocentric. The
hour angle and declination are topocentric. Refraction and
deficiencies in the telescope mounting are ignored. The
purpose of the routine is to give the general form of the
quantities. The details of a real telescope could profoundly
change the results, especially close to the zenith.
4) No range checking of arguments is carried out.
5) In applications which involve many such 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 (for tracking a star)
sine and cosine of declination.
P.T.Wallace Starlink 14 March 1997
Copyright (C) 1997 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
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.endhelp
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