| 1 | /*
|
|---|
| 2 | *+
|
|---|
| 3 | * Name:
|
|---|
| 4 | * palEtrms
|
|---|
| 5 |
|
|---|
| 6 | * Purpose:
|
|---|
| 7 | * Compute the E-terms vector
|
|---|
| 8 |
|
|---|
| 9 | * Language:
|
|---|
| 10 | * Starlink ANSI C
|
|---|
| 11 |
|
|---|
| 12 | * Type of Module:
|
|---|
| 13 | * Library routine
|
|---|
| 14 |
|
|---|
| 15 | * Invocation:
|
|---|
| 16 | * void palEtrms ( double ep, double ev[3] );
|
|---|
| 17 |
|
|---|
| 18 | * Arguments:
|
|---|
| 19 | * ep = double (Given)
|
|---|
| 20 | * Besselian epoch
|
|---|
| 21 | * ev = double [3] (Returned)
|
|---|
| 22 | * E-terms as (dx,dy,dz)
|
|---|
| 23 |
|
|---|
| 24 | * Description:
|
|---|
| 25 | * Computes the E-terms (elliptic component of annual aberration)
|
|---|
| 26 | * vector.
|
|---|
| 27 | *
|
|---|
| 28 | * Note the use of the J2000 aberration constant (20.49552 arcsec).
|
|---|
| 29 | * This is a reflection of the fact that the E-terms embodied in
|
|---|
| 30 | * existing star catalogues were computed from a variety of
|
|---|
| 31 | * aberration constants. Rather than adopting one of the old
|
|---|
| 32 | * constants the latest value is used here.
|
|---|
| 33 | *
|
|---|
| 34 | * See also:
|
|---|
| 35 | * - Smith, C.A. et al., 1989. Astr.J. 97, 265.
|
|---|
| 36 | * - Yallop, B.D. et al., 1989. Astr.J. 97, 274.
|
|---|
| 37 |
|
|---|
| 38 | * Authors:
|
|---|
| 39 | * PTW: Pat Wallace (STFC)
|
|---|
| 40 | * TIMJ: Tim Jenness (JAC, Hawaii)
|
|---|
| 41 | * {enter_new_authors_here}
|
|---|
| 42 |
|
|---|
| 43 | * History:
|
|---|
| 44 | * 2012-02-12 (TIMJ):
|
|---|
| 45 | * Initial version with documentation taken from Fortran SLA
|
|---|
| 46 | * Adapted with permission from the Fortran SLALIB library.
|
|---|
| 47 | * {enter_further_changes_here}
|
|---|
| 48 |
|
|---|
| 49 | * Copyright:
|
|---|
| 50 | * Copyright (C) 1996 Rutherford Appleton Laboratory
|
|---|
| 51 | * Copyright (C) 2012 Science and Technology Facilities Council.
|
|---|
| 52 | * All Rights Reserved.
|
|---|
| 53 |
|
|---|
| 54 | * Licence:
|
|---|
| 55 | * This program is free software: you can redistribute it and/or
|
|---|
| 56 | * modify it under the terms of the GNU Lesser General Public
|
|---|
| 57 | * License as published by the Free Software Foundation, either
|
|---|
| 58 | * version 3 of the License, or (at your option) any later
|
|---|
| 59 | * version.
|
|---|
| 60 | *
|
|---|
| 61 | * This program is distributed in the hope that it will be useful,
|
|---|
| 62 | * but WITHOUT ANY WARRANTY; without even the implied warranty of
|
|---|
| 63 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
|
|---|
| 64 | * GNU Lesser General Public License for more details.
|
|---|
| 65 | *
|
|---|
| 66 | * You should have received a copy of the GNU Lesser General
|
|---|
| 67 | * License along with this program. If not, see
|
|---|
| 68 | * <http://www.gnu.org/licenses/>.
|
|---|
| 69 |
|
|---|
| 70 | * Bugs:
|
|---|
| 71 | * {note_any_bugs_here}
|
|---|
| 72 | *-
|
|---|
| 73 | */
|
|---|
| 74 |
|
|---|
| 75 | #include "pal.h"
|
|---|
| 76 | #include "palmac.h"
|
|---|
| 77 |
|
|---|
| 78 | void palEtrms ( double ep, double ev[3] ) {
|
|---|
| 79 |
|
|---|
| 80 | /* Use the J2000 aberration constant */
|
|---|
| 81 | const double ABCONST = 20.49552;
|
|---|
| 82 |
|
|---|
| 83 | double t, e, e0, p, ek, cp;
|
|---|
| 84 |
|
|---|
| 85 | /* Julian centuries since B1950 */
|
|---|
| 86 | t = (ep - 1950.) * .0100002135903;
|
|---|
| 87 |
|
|---|
| 88 | /* Eccentricity */
|
|---|
| 89 | e = .01673011 - (t * 1.26e-7 + 4.193e-5) * t;
|
|---|
| 90 |
|
|---|
| 91 | /* Mean obliquity */
|
|---|
| 92 | e0 = (84404.836 - ((t * .00181 + .00319) * t + 46.8495) * t) *
|
|---|
| 93 | PAL__DAS2R;
|
|---|
| 94 |
|
|---|
| 95 | /* Mean longitude of perihelion */
|
|---|
| 96 | p = (((t * .012 + 1.65) * t + 6190.67) * t + 1015489.951) *
|
|---|
| 97 | PAL__DAS2R;
|
|---|
| 98 |
|
|---|
| 99 | /* E-terms */
|
|---|
| 100 | ek = e * ABCONST * PAL__DAS2R;
|
|---|
| 101 | cp = cos(p);
|
|---|
| 102 | ev[0] = ek * sin(p);
|
|---|
| 103 | ev[1] = -ek * cp * cos(e0);
|
|---|
| 104 | ev[2] = -ek * cp * sin(e0);
|
|---|
| 105 |
|
|---|
| 106 | }
|
|---|
