1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
|
DOUBLE PRECISION FUNCTION slGMST (UT1)
*+
* - - - - -
* G M S T
* - - - - -
*
* Conversion from universal time to sidereal time (double precision)
*
* Given:
* UT1 dp universal time (strictly UT1) expressed as
* modified Julian Date (JD-2400000.5)
*
* The result is the Greenwich mean sidereal time (double
* precision, radians).
*
* The IAU 1982 expression (see page S15 of 1984 Astronomical Almanac)
* is used, but rearranged to reduce rounding errors. This expression
* is always described as giving the GMST at 0 hours UT. In fact, it
* gives the difference between the GMST and the UT, which happens to
* equal the GMST (modulo 24 hours) at 0 hours UT each day. In this
* routine, the entire UT is used directly as the argument for the
* standard formula, and the fractional part of the UT is added
* separately. Note that the factor 1.0027379... does not appear in the
* IAU 1982 expression explicitly but in the form of the coefficient
* 8640184.812866, which is 86400x36525x0.0027379...
*
* See also the routine slGMSA, which delivers better numerical
* precision by accepting the UT date and time as separate arguments.
*
* Called: slDA2P
*
* P.T.Wallace Starlink 14 October 2001
*
* Copyright (C) 2001 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 UT1
DOUBLE PRECISION slDA2P
DOUBLE PRECISION D2PI,S2R
PARAMETER (D2PI=6.283185307179586476925286766559D0,
: S2R=7.272205216643039903848711535369D-5)
DOUBLE PRECISION TU
* Julian centuries from fundamental epoch J2000 to this UT
TU=(UT1-51544.5D0)/36525D0
* GMST at this UT
slGMST=slDA2P(MOD(UT1,1D0)*D2PI+
: (24110.54841D0+
: (8640184.812866D0+
: (0.093104D0-6.2D-6*TU)*TU)*TU)*S2R)
END
|
