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Diffstat (limited to 'src/slalib/aop.f')
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diff --git a/src/slalib/aop.f b/src/slalib/aop.f new file mode 100644 index 0000000..66ef9c4 --- /dev/null +++ b/src/slalib/aop.f @@ -0,0 +1,174 @@ + SUBROUTINE sla_AOP (RAP, DAP, DATE, DUT, ELONGM, PHIM, HM, + : XP, YP, TDK, PMB, RH, WL, TLR, + : AOB, ZOB, HOB, DOB, ROB) +*+ +* - - - - +* A O P +* - - - - +* +* Apparent to observed place, for optical sources distant from +* the solar system. +* +* Given: +* RAP d geocentric apparent right ascension +* DAP d geocentric apparent declination +* 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=273.155D0) +* PMB d local atmospheric pressure (mB; std=1013.25D0) +* RH d local relative humidity (in the range 0D0-1D0) +* WL d effective wavelength (micron, e.g. 0.55D0) +* TLR d tropospheric lapse rate (DegK/metre, e.g. 0.0065D0) +* +* Returned: +* AOB d observed azimuth (radians: N=0,E=90) +* ZOB d observed zenith distance (radians) +* HOB d observed Hour Angle (radians) +* DOB d observed Declination (radians) +* ROB d observed Right Ascension (radians) +* +* Notes: +* +* 1) This routine returns zenith distance 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 +* sla_REFRO routine returns a fixed value of the refraction. +* The complementary routines sla_AOP (or sla_AOPQK) and sla_OAP +* (or sla_OAPQK) 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) "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 sla_MAP 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 +* sla_FK425 etc routines. +* +* 5) "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. +* +* 6) 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. +* +* 7) 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 sla_AOPPA once followed by one call per star to sla_AOPQK. +* Where a range of times within a limited period of a few hours +* is involved, and the highest precision is not required, call +* sla_AOPPA once, followed by a call to sla_AOPPAT each time the +* time changes, followed by one call per star to sla_AOPQK. +* +* 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 +* sla_OBS 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=0D0. 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 sla_OBS. If P, +* the pressure in millibars, is available, an adequate +* estimate of HM can be obtained from the expression +* +* HM ~ -29.3D0*TSL*LOG(P/1013.25D0). +* +* 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 ~ 1013.25D0*EXP(-HM/(29.3D0*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 produced by the present routine are with +* respect to the celestial pole. Corrections to the terrestrial +* pole can be computed using sla_POLMO. +* +* Called: sla_AOPPA, sla_AOPQK +* +* P.T.Wallace Starlink 6 September 1999 +* +* Copyright (C) 1999 P.T.Wallace and CCLRC +*- + + IMPLICIT NONE + + DOUBLE PRECISION RAP,DAP,DATE,DUT,ELONGM,PHIM,HM, + : XP,YP,TDK,PMB,RH,WL,TLR,AOB,ZOB,HOB,DOB,ROB + + DOUBLE PRECISION AOPRMS(14) + + + CALL sla_AOPPA(DATE,DUT,ELONGM,PHIM,HM,XP,YP,TDK,PMB,RH,WL,TLR, + : AOPRMS) + CALL sla_AOPQK(RAP,DAP,AOPRMS,AOB,ZOB,HOB,DOB,ROB) + + END |