1 /**************************************************************************
3 * Written by Durk Talsma. Originally started October 1997, for distribution
4 * with the FlightGear project. Version 2 was written in August and
5 * September 1998. This code is based upon algorithms and data kindly
6 * provided by Mr. Paul Schlyter. (pausch@saaf.se).
8 * This library is free software; you can redistribute it and/or
9 * modify it under the terms of the GNU Library General Public
10 * License as published by the Free Software Foundation; either
11 * version 2 of the License, or (at your option) any later version.
13 * This library is distributed in the hope that it will be useful,
14 * but WITHOUT ANY WARRANTY; without even the implied warranty of
15 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
16 * Library General Public License for more details.
18 * You should have received a copy of the GNU General Public License
19 * along with this program; if not, write to the Free Software
20 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
23 **************************************************************************/
27 #include <simgear/debug/logstream.hxx>
32 /*************************************************************************
33 * Star::Star(double mjd)
34 * Public constructor for class Star
35 * Argument: The current time.
36 * the hard coded orbital elements our sun are passed to
37 * CelestialBody::CelestialBody();
38 * note that the word sun is avoided, in order to prevent some compilation
39 * problems on sun systems
40 ************************************************************************/
41 Star::Star(double mjd) :
42 CelestialBody (0.000000, 0.0000000000,
44 282.9404, 4.7093500E-5,
47 356.0470, 0.98560025850, mjd)
53 CelestialBody (0.000000, 0.0000000000,
55 282.9404, 4.7093500E-5,
58 356.0470, 0.98560025850)
68 /*************************************************************************
69 * void Star::updatePosition(double mjd, Star *ourSun)
71 * calculates the current position of our sun.
72 *************************************************************************/
73 void Star::updatePosition(double mjd)
80 updateOrbElements(mjd);
82 actTime = sgCalcActTime(mjd);
83 ecl = SGD_DEGREES_TO_RADIANS * (23.4393 - 3.563E-7 * actTime); // Angle in Radians
84 eccAnom = sgCalcEccAnom(M, e); // Calculate the eccentric Anomaly (also known as solving Kepler's equation)
86 xv = cos(eccAnom) - e;
87 yv = sqrt (1.0 - e*e) * sin(eccAnom);
88 v = atan2 (yv, xv); // the sun's true anomaly
89 distance = r = sqrt (xv*xv + yv*yv); // and its distance
91 lonEcl = v + w; // the sun's true longitude
94 // convert the sun's true longitude to ecliptic rectangular
95 // geocentric coordinates (xs, ys)
96 xs = r * cos (lonEcl);
97 ys = r * sin (lonEcl);
99 // convert ecliptic coordinates to equatorial rectangular
100 // geocentric coordinates
106 // And finally, calculate right ascension and declination
107 rightAscension = atan2 (ye, xe);
108 declination = atan2 (ze, sqrt (xe*xe + ye*ye));