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diff --git a/math/slalib/doc/planet.hlp b/math/slalib/doc/planet.hlp new file mode 100644 index 00000000..3bdb7b9f --- /dev/null +++ b/math/slalib/doc/planet.hlp @@ -0,0 +1,130 @@ +.help planet Jun99 "Slalib Package" +.nf + + SUBROUTINE slPLNT (DATE, NP, PV, JSTAT) + + - - - - - - - + P L N T + - - - - - - - + + Approximate heliocentric position and velocity of a specified + major planet. + + Given: + DATE d Modified Julian Date (JD - 2400000.5) + NP i planet (1=Mercury, 2=Venus, 3=EMB ... 9=Pluto) + + Returned: + PV d(6) heliocentric x,y,z,xdot,ydot,zdot, J2000 + equatorial triad (AU,AU/s) + JSTAT i status: +1 = warning: date out of range + 0 = OK + -1 = illegal NP (outside 1-9) + -2 = solution didn't converge + + Called: slPLNE + + Notes + + 1 The epoch, DATE, is in the TDB timescale and is a Modified + Julian Date (JD-2400000.5). + + 2 The reference frame is equatorial and is with respect to the + mean equinox and ecliptic of epoch J2000. + + 3 If an NP value outside the range 1-9 is supplied, an error + status (JSTAT = -1) is returned and the PV vector set to zeroes. + + 4 The algorithm for obtaining the mean elements of the planets + from Mercury to Neptune is due to J.L. Simon, P. Bretagnon, + J. Chapront, M. Chapront-Touze, G. Francou and J. Laskar + (Bureau des Longitudes, Paris). The (completely different) + algorithm for calculating the ecliptic coordinates of Pluto + is by Meeus. + + 5 Comparisons of the present routine with the JPL DE200 ephemeris + give the following RMS errors over the interval 1960-2025: + + position (km) speed (metre/sec) + + Mercury 334 0.437 + Venus 1060 0.855 + EMB 2010 0.815 + Mars 7690 1.98 + Jupiter 71700 7.70 + Saturn 199000 19.4 + Uranus 564000 16.4 + Neptune 158000 14.4 + Pluto 36400 0.137 + + From comparisons with DE102, Simon et al quote the following + longitude accuracies over the interval 1800-2200: + + Mercury 4" + Venus 5" + EMB 6" + Mars 17" + Jupiter 71" + Saturn 81" + Uranus 86" + Neptune 11" + + In the case of Pluto, Meeus quotes an accuracy of 0.6 arcsec + in longitude and 0.2 arcsec in latitude for the period + 1885-2099. + + For all except Pluto, over the period 1000-3000 the accuracy + is better than 1.5 times that over 1800-2200. Outside the + period 1000-3000 the accuracy declines. For Pluto the + accuracy declines rapidly outside the period 1885-2099. + Outside these ranges (1885-2099 for Pluto, 1000-3000 for + the rest) a "date out of range" warning status (JSTAT=+1) + is returned. + + 6 The algorithms for (i) Mercury through Neptune and (ii) Pluto + are completely independent. In the Mercury through Neptune + case, the present SLALIB implementation differs from the + original Simon et al Fortran code in the following respects. + + * The date is supplied as a Modified Julian Date rather + than a Julian Date (MJD = JD - 2400000.5). + + * The result is returned only in equatorial Cartesian form; + the ecliptic longitude, latitude and radius vector are not + returned. + + * The velocity is in AU per second, not AU per day. + + * Different error/warning status values are used. + + * Kepler's equation is not solved inline. + + * Polynomials in T are nested to minimize rounding errors. + + * Explicit double-precision constants are used to avoid + mixed-mode expressions. + + * There are other, cosmetic, changes to comply with + Starlink/SLALIB style guidelines. + + None of the above changes affects the result significantly. + + 7 For NP=3 the result is for the Earth-Moon Barycentre. To + obtain the heliocentric position and velocity of the Earth, + either use the SLALIB routine slEVP or call slDMON and + subtract 0.012150581 times the geocentric Moon vector from + the EMB vector produced by the present routine. (The Moon + vector should be precessed to J2000 first, but this can + be omitted for modern epochs without introducing significant + inaccuracy.) + + References: Simon et al., Astron. Astrophys. 282, 663 (1994). + Meeus, Astronomical Algorithms, Willmann-Bell (1991). + + P.T.Wallace Starlink 27 May 1997 + + Copyright (C) 1997 Rutherford Appleton Laboratory + Copyright (C) 1995 Association of Universities for Research in Astronomy Inc. + +.fi +.endhelp |