nova.proper_motion source code

1 /*
2  *  This library is free software; you can redistribute it and/or
3  *  modify it under the terms of the GNU Lesser General Public
4  *  License as published by the Free Software Foundation; either
5  *  version 2 of the License, or (at your option) any later version.
6  *
7  *  This library is distributed in the hope that it will be useful,
8  *  but WITHOUT ANY WARRANTY; without even the implied warranty of
9  *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
10  *  Lesser General Public License for more details.
11  *
12  *  You should have received a copy of the GNU General Public License
13  *  along with this program; if not, write to the Free Software
14  *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
15  *
16  *  Copyright (C) 2000 - 2005 Liam Girdwood <lgirdwood@gmail.com>
17  */
18 
19 module nova.proper_motion;
20 
21 import nova.utility;
22 import nova.ln_types;
23 
24 extern (C) {
25 
26 /*
27 ** Proper Motion.
28 */
29 
30 /*! \fn void ln_get_equ_pm(struct ln_equ_posn *mean_position, struct ln_equ_posn *proper_motion, double JD, struct ln_equ_posn *position)
31 * \param mean_position Mean position of object.
32 * \param proper_motion Annual Proper motion of object.
33 * \param JD Julian Day.
34 * \param position Pointer to store new object position.
35 *
36 * Calculate a stars equatorial coordinates from it's mean coordinates (J2000.0)
37 * with the effects of proper motion for a given Julian Day.
38 */
39 /* Example 20.b pg 126
40 */
41 @nogc void ln_get_equ_pm(const ref ln_equ_posn mean_position,
42 	const ref ln_equ_posn proper_motion, double JD, ref ln_equ_posn position) nothrow
43 {
44 	ln_get_equ_pm_epoch (mean_position, proper_motion, JD, JD2000, position);
45 }
46 
47 /*!
48 * \param mean_position Mean position of object.
49 * \param proper_motion Annual Proper motion of object.
50 * \param JD Julian Day.
51 * \param epoch_JD Mean position epoch in JD
52 * \param position Pointer to store new object position.
53 *
54 * Calculate a stars equatorial coordinates from it's mean coordinates and epoch
55 * with the effects of proper motion for a given Julian Day.
56 */
57 /* Example 20.b, pg 126
58 */
59 @nogc void ln_get_equ_pm_epoch(const ref ln_equ_posn mean_position,
60 	const ref ln_equ_posn proper_motion, double JD, double epoch_JD,
61 	ref ln_equ_posn position) nothrow
62 {
63 	real T;
64 
65 	T = (JD - epoch_JD) / 365.25;
66 
67 	/* calc proper motion */
68 	position.ra = mean_position.ra + T * proper_motion.ra;
69 	position.dec = mean_position.dec + T * proper_motion.dec;
70 
71 	/* change to degrees */
72 	position.ra = ln_range_degrees(position.ra);
73 }
74 
75 }