From fa080de7afc95aa1c19a6e6fc0e0708ced2eadc4 Mon Sep 17 00:00:00 2001 From: Joseph Hunkeler Date: Wed, 8 Jul 2015 20:46:52 -0400 Subject: Initial commit --- math/slalib/doc/dt.hlp | 55 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 55 insertions(+) create mode 100644 math/slalib/doc/dt.hlp (limited to 'math/slalib/doc/dt.hlp') diff --git a/math/slalib/doc/dt.hlp b/math/slalib/doc/dt.hlp new file mode 100644 index 00000000..65ddca29 --- /dev/null +++ b/math/slalib/doc/dt.hlp @@ -0,0 +1,55 @@ +.help dt Jun99 "Slalib Package" +.nf + + DOUBLE PRECISION FUNCTION slDT (EPOCH) + + - - - + D T + - - - + + Estimate the offset between dynamical time and Universal Time + for a given historical epoch. + + Given: + EPOCH d (Julian) epoch (e.g. 1850D0) + + The result is a rough estimate of ET-UT (after 1984, TT-UT) at + the given epoch, in seconds. + + Notes: + + 1 Depending on the epoch, one of three parabolic approximations + is used: + + before 979 Stephenson & Morrison's 390 BC to AD 948 model + 979 to 1708 Stephenson & Morrison's 948 to 1600 model + after 1708 McCarthy & Babcock's post-1650 model + + The breakpoints are chosen to ensure continuity: they occur + at places where the adjacent models give the same answer as + each other. + + 2 The accuracy is modest, with errors of up to 20 sec during + the interval since 1650, rising to perhaps 30 min by 1000 BC. + Comparatively accurate values from AD 1600 are tabulated in + the Astronomical Almanac (see section K8 of the 1995 AA). + + 3 The use of double-precision for both argument and result is + purely for compatibility with other SLALIB time routines. + + 4 The models used are based on a lunar tidal acceleration value + of -26.00 arcsec per century. + + Reference: Explanatory Supplement to the Astronomical Almanac, + ed P.K.Seidelmann, University Science Books (1992), + section 2.553, p83. This contains references to + the Stephenson & Morrison and McCarthy & Babcock + papers. + + P.T.Wallace Starlink 1 March 1995 + + Copyright (C) 1995 Rutherford Appleton Laboratory + Copyright (C) 1995 Association of Universities for Research in Astronomy Inc. + +.fi +.endhelp -- cgit