
ACTION:
 Positions, velocities and accelerations for an altazimuth telescope mount that is
tracking a star (double precision).

CALL:
CALL sla_ALTAZ (HA, DEC, PHI,
AZ, AZD, AZDD, EL, ELD, ELDD, PA, PAD, PADD)
GIVEN:
HA  D  hour angle 

DEC  D  declination 

PHI  D  observatory latitude 

RETURNED:
AZ  D  azimuth 

AZD  D  azimuth velocity 

AZDD  D  azimuth acceleration 

EL  D  elevation 

ELD  D  elevation velocity 

ELDD  D  elevation acceleration 

PA  D  parallactic angle 

PAD  D  parallactic angle velocity 

PADD  D  parallactic angle 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 secondbased units:
angles  $\times 360/2\pi $  $\to $  degrees 
velocities  $\times \left(2\pi /86400\right)\times \left(360/2\pi \right)$  $\to $  degree/sec 
accelerations  $\times {\left(2\pi /86400\right)}^{2}\times \left(360/2\pi \right)$  $\to $  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 $\left[\phantom{\rule{0.3em}{0ex}}0,2\pi \phantom{\rule{0.3em}{0ex}}\right]$;
north is zero, and east is $+\pi /2$.
Elevation and parallactic angle are returned in the range
$\pm \pi $.
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.