From 40e5a5811c6ffce9b0974e93cdd927cbcf60c157 Mon Sep 17 00:00:00 2001 From: Joe Hunkeler Date: Tue, 11 Aug 2015 16:51:37 -0400 Subject: Repatch (from linux) of OSX IRAF --- math/slalib/dt.f | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 97 insertions(+) create mode 100644 math/slalib/dt.f (limited to 'math/slalib/dt.f') diff --git a/math/slalib/dt.f b/math/slalib/dt.f new file mode 100644 index 00000000..a012c677 --- /dev/null +++ b/math/slalib/dt.f @@ -0,0 +1,97 @@ + 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 +* +* License: +* 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 2 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 (see SLA_CONDITIONS); if not, write to the +* Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, +* Boston, MA 02110-1301 USA +* +* Copyright (C) 1995 Association of Universities for Research in Astronomy Inc. +*- + + IMPLICIT NONE + + DOUBLE PRECISION EPOCH + DOUBLE PRECISION T,W,S + + +* Centuries since 1800 + T=(EPOCH-1800D0)/100D0 + +* Select model + IF (EPOCH.GE.1708.185161980887D0) THEN + +* Post-1708: use McCarthy & Babcock + W=T-0.19D0 + S=5.156D0+13.3066D0*W*W + ELSE IF (EPOCH.GE.979.0258204760233D0) THEN + +* 979-1708: use Stephenson & Morrison's 948-1600 model + S=25.5D0*T*T + ELSE + +* Pre-979: use Stephenson & Morrison's 390 BC to AD 948 model + S=1360.0D0+(320D0+44.3D0*T)*T + END IF + +* Result + slDT=S + + END -- cgit