/* *+ * Name: * palAop * Purpose: * Apparent to observed place * Language: * Starlink ANSI C * Type of Module: * Library routine * Invocation: * void palAop ( double rap, double dap, 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 *aob, double *zob, double *hob, * double *dob, double *rob ); * Arguments: * rap = double (Given) * Geocentric apparent right ascension * dap = double (Given) * Geocentirc apparent declination * date = double (Given) * UTC date/time (Modified Julian Date, JD-2400000.5) * dut = double (Given) * delta UT: UT1-UTC (UTC seconds) * elongm = double (Given) * Mean longitude of the observer (radians, east +ve) * phim = double (Given) * Mean geodetic latitude of the observer (radians) * hm = double (Given) * Observer's height above sea level (metres) * xp = double (Given) * Polar motion x-coordinates (radians) * yp = double (Given) * Polar motion y-coordinates (radians) * tdk = double (Given) * Local ambient temperature (K; std=273.15) * pmb = double (Given) * Local atmospheric pressure (mb; std=1013.25) * rh = double (Given) * Local relative humidity (in the range 0.0-1.0) * wl = double (Given) * Effective wavelength (micron, e.g. 0.55) * tlr = double (Given) * Tropospheric laps rate (K/metre, e.g. 0.0065) * aob = double * (Returned) * Observed azimuth (radians: N=0; E=90) * zob = double * (Returned) * Observed zenith distance (radians) * hob = double * (Returned) * Observed Hour Angle (radians) * dob = double * (Returned) * Observed Declination (radians) * rob = double * (Returned) * Observed Right Ascension (radians) * Description: * Apparent to observed place for sources distant from the solar system. * Authors: * PTW: Patrick T. Wallace * TIMJ: Tim Jenness (JAC, Hawaii) * {enter_new_authors_here} * Notes: * - This routine returns zenith distance rather than elevation * in order to reflect the fact that no allowance is made for * depression of the horizon. * * - 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 * palRefro routine returns a fixed value of the refraction. * The complementary routines palAop (or palAopqk) and palOap * (or palOapqk) are self-consistent to better than 1 micro- * arcsecond all over the celestial sphere. * * - 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. * * - "Apparent" place means the geocentric apparent right ascension * and declination, which is obtained from a catalogue mean place * by allowing for space motion, parallax, precession, nutation, * annual aberration, and the Sun's gravitational lens effect. For * star positions in the FK5 system (i.e. J2000), these effects can * be applied by means of the palMap etc routines. Starting from * other mean place systems, additional transformations will be * needed; for example, FK4 (i.e. B1950) mean places would first * have to be converted to FK5, which can be done with the * palFk425 etc routines. * * - "Observed" Az,El means the position that would be seen by a * perfect theodolite located at the observer. This is obtained * from the geocentric apparent RA,Dec by allowing for Earth * orientation and diurnal aberration, rotating from equator * to horizon coordinates, and then adjusting for refraction. * The HA,Dec is obtained by rotating back into equatorial * coordinates, using the geodetic latitude corrected for polar * motion, and is 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). Finally, the RA is obtained by subtracting * the HA from the local apparent ST. * * - To predict the required setting of a real telescope, the * observed place produced by this routine would have to be * adjusted for the tilt of the azimuth or polar axis of the * mounting (with appropriate corrections for mount flexures), * for non-perpendicularity between the mounting axes, for the * position of the rotator axis and the pointing axis relative * to it, for tube flexure, for gear and encoder errors, and * finally for encoder zero points. Some telescopes would, of * course, exhibit other properties which would need to be * accounted for at the appropriate point in the sequence. * * - This routine takes time to execute, due mainly to the * rigorous integration used to evaluate the refraction. * For processing multiple stars for one location and time, * call palAoppa once followed by one call per star to palAopqk. * Where a range of times within a limited period of a few hours * is involved, and the highest precision is not required, call * palAoppa once, followed by a call to palAoppat each time the * time changes, followed by one call per star to palAopqk. * * - 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. * * - 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. * * - 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 * palObs routine are west-positive, following astronomical * usage, and must be reversed in sign before use in the present * routine. * * - 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. * * - 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 palObs. 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 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 nearly proportional to the * pressure and that an accurate P value is important for precise * work. * * - The azimuths etc produced by the present routine are with * respect to the celestial pole. Corrections to the terrestrial * pole can be computed using palPolmo. * History: * 2012-08-25 (TIMJ): * Initial version * Adapted with permission from the Fortran SLALIB library. * {enter_further_changes_here} * Copyright: * Copyright (C) 2005 Patrick T. Wallace * Copyright (C) 2012 Science and Technology Facilities Council. * All Rights Reserved. * Licence: * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License as * published by the Free Software Foundation; either version 3 of * the License, or (at your option) any later version. * * This program is distributed in the hope that it will be * useful, but WITHOUT ANY WARRANTY; without even the implied * warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR * PURPOSE. See the GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, * MA 02110-1301, USA. * Bugs: * {note_any_bugs_here} *- */ #include "pal.h" void palAop ( double rap, double dap, 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 *aob, double *zob, double *hob, double *dob, double *rob ) { double aoprms[14]; palAoppa(date,dut,elongm,phim,hm,xp,yp,tdk,pmb,rh,wl,tlr, aoprms); palAopqk(rap,dap,aoprms,aob,zob,hob,dob,rob); }