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diff --git a/math/slalib/doc/aoppa.hlp b/math/slalib/doc/aoppa.hlp new file mode 100644 index 00000000..f96d835b --- /dev/null +++ b/math/slalib/doc/aoppa.hlp @@ -0,0 +1,114 @@ +.help aoppa Jun99 "Slalib Package" +.nf + + SUBROUTINE slAOPA (DATE, DUT, ELONGM, PHIM, HM, + : XP, YP, TDK, PMB, RH, WL, TLR, AOPRMS) + + - - - - - - + A O P A + - - - - - - + + Precompute apparent to observed place parameters required by + slAOPQ and slOAPQ. + + Given: + 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: + 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 (TDK) + (7) pressure (PMB) + (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) + + Notes: + + 1) 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. + + 2) The DATE argument is UTC expressed as an MJD. This is, + strictly speaking, improper, 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. + + 3) 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. + + 4) 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 + slOBS routine are west-positive, following astronomical + usage, and must be reversed in sign before use in the present + routine. + + 5) 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. + + 6) 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 slOBS. 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. + + 7) Repeated, computationally-expensive, calls to slAOPA for + times that are very close together can be avoided by calling + slAOPA just once and then using slAOPT for the subsequent + times. Fresh calls to slAOPA will be needed only when changes + in the precession have grown to unacceptable levels or when + anything affecting the refraction has changed. + + Called: slGEOC, slRFCO, slEQEX, slAOPT + + P.T.Wallace Starlink 9 June 1998 + + Copyright (C) 1998 Rutherford Appleton Laboratory + Copyright (C) 1995 Association of Universities for Research in Astronomy Inc. + +.fi +.endhelp |