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.help oapqk Jun99 "Slalib Package"
.nf
SUBROUTINE slOAPQ (TYPE, OB1, OB2, AOPRMS, RAP, DAP)
- - - - - -
O A P Q
- - - - - -
Quick observed to apparent place
Given:
TYPE c*(*) type of coordinates - 'R', 'H' or 'A' (see below)
OB1 d observed Az, HA or RA (radians; Az is N=0,E=90)
OB2 d observed ZD or Dec (radians)
AOPRMS d(14) star-independent apparent-to-observed parameters:
(1) geodetic latitude (radians)
(2,3) sine and cosine of geodetic latitude
(4) magnitude of diurnal aberration vector
(5) height (HM)
(6) ambient temperature (T)
(7) pressure (P)
(8) relative humidity (RH)
(9) wavelength (WL)
(10) lapse rate (TLR)
(11,12) refraction constants A and B (radians)
(13) longitude + eqn of equinoxes + sidereal DUT (radians)
(14) local apparent sidereal time (radians)
Returned:
RAP d geocentric apparent right ascension
DAP d geocentric apparent declination
Notes:
1) Only the first character of the TYPE argument is significant.
'R' or 'r' indicates that OBS1 and OBS2 are the observed Right
Ascension and Declination; 'H' or 'h' indicates that they are
Hour Angle (West +ve) and Declination; anything else ('A' or
'a' is recommended) indicates that OBS1 and OBS2 are Azimuth
(North zero, East is 90 deg) and zenith distance. (Zenith
distance is used rather than elevation in order to reflect the
fact that no allowance is made for depression of the horizon.)
2) The accuracy of the result is limited by the corrections for
refraction. Providing the meteorological parameters are
known accurately and there are no gross local effects, the
predicted apparent RA,Dec should be within about 0.1 arcsec
for a zenith distance of less than 70 degrees. Even at a
topocentric zenith distance of 90 degrees, the accuracy in
elevation should be better than 1 arcmin; useful results
are available for a further 3 degrees, beyond which the
slRFRO routine returns a fixed value of the refraction.
The complementary routines slAOP (or slAOPQ) and slOAP
(or slOAPQ) are self-consistent to better than 1 micro-
arcsecond all over the celestial sphere.
3) It is advisable to take great care with units, as even
unlikely values of the input parameters are accepted and
processed in accordance with the models used.
5) "Observed" Az,El means the position that would be seen by a
perfect theodolite located at the observer. This is
related to the observed HA,Dec via the standard rotation, using
the geodetic latitude (corrected for polar motion), while the
observed HA and RA are related simply through the local
apparent ST. "Observed" RA,Dec or HA,Dec thus means the
position that would be seen by a perfect equatorial located
at the observer and with its polar axis aligned to the
Earth's axis of rotation (n.b. not to the refracted pole).
By removing from the observed place the effects of
atmospheric refraction and diurnal aberration, the
geocentric apparent RA,Dec is obtained.
5) Frequently, mean rather than apparent RA,Dec will be required,
in which case further transformations will be necessary. The
slAMP etc routines will convert the apparent RA,Dec produced
by the present routine into an "FK5" (J2000) mean place, by
allowing for the Sun's gravitational lens effect, annual
aberration, nutation and precession. Should "FK4" (1950)
coordinates be needed, the routines slFK54 etc will also
need to be applied.
6) To convert to apparent RA,Dec the coordinates read from a
real telescope, corrections would have to be applied for
encoder zero points, gear and encoder errors, tube flexure,
the position of the rotator axis and the pointing axis
relative to it, non-perpendicularity between the mounting
axes, and finally for the tilt of the azimuth or polar axis
of the mounting (with appropriate corrections for mount
flexures). Some telescopes would, of course, exhibit other
properties which would need to be accounted for at the
appropriate point in the sequence.
7) The star-independent apparent-to-observed-place parameters
in AOPRMS may be computed by means of the slAOPA routine.
If nothing has changed significantly except the time, the
slAOPT routine may be used to perform the requisite
partial recomputation of AOPRMS.
8) The azimuths etc used by the present routine are with respect
to the celestial pole. Corrections from the terrestrial pole
can be computed using slPLMO.
Called: slDS2C, slDC2S, slRFRO, slDA2P
P.T.Wallace Starlink 23 June 1997
Copyright (C) 1996 Rutherford Appleton Laboratory
Copyright (C) 1995 Association of Universities for Research in Astronomy Inc.
.fi
.endhelp
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