#include "slalib.h" #include "slamac.h" void slaOap ( char *type, double ob1, double ob2, double date, double dut, double elongm, double phim, double hm, double xp, double yp, double tdk, double pmb, double rh, double wl, double tlr, double *rap, double *dap ) /* ** - - - - - - - ** s l a O a p ** - - - - - - - ** ** 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) ** date d UTC date/time (modified Julian Date, JD-2400000.5) ** dut d delta UT: UT1-UTC (UTC seconds) ** elongm d mean longitude of the observer (radians, east +ve) ** phim d mean geodetic latitude of the observer (radians) ** hm d observer's height above sea level (metres) ** xp d polar motion x-coordinate (radians) ** yp d polar motion y-coordinate (radians) ** tdk d local ambient temperature (DegK; std=273.155) ** pmb d local atmospheric pressure (mB; std=1013.25) ** rh d local relative humidity (in the range 0.0-1.0) ** wl d effective wavelength (micron, e.g. 0.55) ** tlr d tropospheric lapse rate (DegK/metre, e.g. 0.0065) ** ** 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 ** slaRefro routine returns a fixed value of the refraction. ** The complementary routines slaAop (or slaAopqk) and slaOap ** (or slaOapqk) 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. ** ** 4) "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 ** slaAMP 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 slaFk425 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 slaAoppa routine. ** If nothing has changed significantly except the time, the ** slaAoppat routine may be used to perform the requisite ** partial recomputation of aoprms. ** ** 8) The date argument is UTC expressed as an MJD. This is, ** strictly speaking, wrong, because of leap seconds. However, ** as long as the delta UT and the UTC are consistent there ** are no difficulties, except during a leap second. In this ** case, the start of the 61st second of the final minute should ** begin a new MJD day and the old pre-leap delta UT should ** continue to be used. As the 61st second completes, the MJD ** should revert to the start of the day as, simultaneously, ** the delta UTC changes by one second to its post-leap new value. ** ** 9) The delta UT (UT1-UTC) is tabulated in IERS circulars and ** elsewhere. It increases by exactly one second at the end of ** each UTC leap second, introduced in order to keep delta UT ** within +/- 0.9 seconds. ** ** 10) IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION. ** The longitude required by the present routine is east-positive, ** in accordance with geographical convention (and right-handed). ** In particular, note that the longitudes returned by the ** slaObs routine are west-positive, following astronomical ** usage, and must be reversed in sign before use in the present ** routine. ** ** 11) The polar coordinates xp,yp can be obtained from IERS ** circulars and equivalent publications. The maximum amplitude ** is about 0.3 arcseconds. If xp,yp values are unavailable, ** use xp=yp=0.0. See page B60 of the 1988 Astronomical Almanac ** for a definition of the two angles. ** ** 12) The height above sea level of the observing station, hm, ** can be obtained from the Astronomical Almanac (Section J ** in the 1988 edition), or via the routine slaObs. If p, ** the pressure in millibars, is available, an adequate ** estimate of hm can be obtained from the expression ** ** hm = -29.3 * tsl * log ( p / 1013.25 ); ** ** where tsl is the approximate sea-level air temperature ** in deg K (See Astrophysical Quantities, C.W.Allen, ** 3rd edition, section 52). Similarly, if the pressure p ** is not known, it can be estimated from the height of the ** observing station, hm as follows: ** ** p = 1013.25 * exp ( -hm / ( 29.3 * tsl ) ); ** ** Note, however, that the refraction is proportional to the ** pressure and that an accurate p value is important for ** precise work. ** ** 13) The azimuths etc used by the present routine are with respect ** to the celestial pole. Corrections from the terrestrial pole ** can be computed using slaPolmo. ** ** Called: slaAoppa, slaOapqk ** ** Last revision: 6 September 1999 ** ** Copyright P.T.Wallace. All rights reserved. */ { double aoprms[14]; slaAoppa ( date, dut, elongm, phim, hm, xp, yp, tdk, pmb, rh, wl, tlr, aoprms ); slaOapqk ( type, ob1, ob2, aoprms, rap, dap ); }