/* +----------------------------------------------------------------------+ | PHP Version 5 | +----------------------------------------------------------------------+ | Copyright (c) 1997-2007 The PHP Group | +----------------------------------------------------------------------+ | This source file is subject to version 3.01 of the PHP license, | | that is bundled with this package in the file LICENSE, and is | | available through the world-wide-web at the following url: | | http://www.php.net/license/3_01.txt | | If you did not receive a copy of the PHP license and are unable to | | obtain it through the world-wide-web, please send a note to | | license@php.net so we can mail you a copy immediately. | +----------------------------------------------------------------------+ | Algorithms are taken from a public domain source by Paul | | Schlyter, who wrote this in December 1992 | +----------------------------------------------------------------------+ | Authors: Derick Rethans <derick@derickrethans.nl> | +----------------------------------------------------------------------+ */ /* $Id: astro.c,v 1.1.2.4.2.1 2007/01/01 09:35:48 sebastian Exp $ */ #include <stdio.h> #include <math.h> #include "timelib.h" #define days_since_2000_Jan_0(y,m,d) \ (367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L) #ifndef PI #define PI 3.1415926535897932384 #endif #define RADEG ( 180.0 / PI ) #define DEGRAD ( PI / 180.0 ) /* The trigonometric functions in degrees */ #define sind(x) sin((x)*DEGRAD) #define cosd(x) cos((x)*DEGRAD) #define tand(x) tan((x)*DEGRAD) #define atand(x) (RADEG*atan(x)) #define asind(x) (RADEG*asin(x)) #define acosd(x) (RADEG*acos(x)) #define atan2d(y,x) (RADEG*atan2(y,x)) /* Following are some macros around the "workhorse" function __daylen__ */ /* They mainly fill in the desired values for the reference altitude */ /* below the horizon, and also selects whether this altitude should */ /* refer to the Sun's center or its upper limb. */ #include "astro.h" /******************************************************************/ /* This function reduces any angle to within the first revolution */ /* by subtracting or adding even multiples of 360.0 until the */ /* result is >= 0.0 and < 360.0 */ /******************************************************************/ #define INV360 (1.0 / 360.0) /*****************************************/ /* Reduce angle to within 0..360 degrees */ /*****************************************/ static double astro_revolution(double x) { return (x - 360.0 * floor(x * INV360)); } /*********************************************/ /* Reduce angle to within +180..+180 degrees */ /*********************************************/ static double astro_rev180( double x ) { return (x - 360.0 * floor(x * INV360 + 0.5)); } /*******************************************************************/ /* This function computes GMST0, the Greenwich Mean Sidereal Time */ /* at 0h UT (i.e. the sidereal time at the Greenwhich meridian at */ /* 0h UT). GMST is then the sidereal time at Greenwich at any */ /* time of the day. I've generalized GMST0 as well, and define it */ /* as: GMST0 = GMST - UT -- this allows GMST0 to be computed at */ /* other times than 0h UT as well. While this sounds somewhat */ /* contradictory, it is very practical: instead of computing */ /* GMST like: */ /* */ /* GMST = (GMST0) + UT * (366.2422/365.2422) */ /* */ /* where (GMST0) is the GMST last time UT was 0 hours, one simply */ /* computes: */ /* */ /* GMST = GMST0 + UT */ /* */ /* where GMST0 is the GMST "at 0h UT" but at the current moment! */ /* Defined in this way, GMST0 will increase with about 4 min a */ /* day. It also happens that GMST0 (in degrees, 1 hr = 15 degr) */ /* is equal to the Sun's mean longitude plus/minus 180 degrees! */ /* (if we neglect aberration, which amounts to 20 seconds of arc */ /* or 1.33 seconds of time) */ /* */ /*******************************************************************/ static double astro_GMST0(double d) { double sidtim0; /* Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr */ /* L = M + w, as defined in sunpos(). Since I'm too lazy to */ /* add these numbers, I'll let the C compiler do it for me. */ /* Any decent C compiler will add the constants at compile */ /* time, imposing no runtime or code overhead. */ sidtim0 = astro_revolution((180.0 + 356.0470 + 282.9404) + (0.9856002585 + 4.70935E-5) * d); return sidtim0; } /* This function computes the Sun's position at any instant */ /******************************************************/ /* Computes the Sun's ecliptic longitude and distance */ /* at an instant given in d, number of days since */ /* 2000 Jan 0.0. The Sun's ecliptic latitude is not */ /* computed, since it's always very near 0. */ /******************************************************/ static void astro_sunpos(double d, double *lon, double *r) { double M, /* Mean anomaly of the Sun */ w, /* Mean longitude of perihelion */ /* Note: Sun's mean longitude = M + w */ e, /* Eccentricity of Earth's orbit */ E, /* Eccentric anomaly */ x, y, /* x, y coordinates in orbit */ v; /* True anomaly */ /* Compute mean elements */ M = astro_revolution(356.0470 + 0.9856002585 * d); w = 282.9404 + 4.70935E-5 * d; e = 0.016709 - 1.151E-9 * d; /* Compute true longitude and radius vector */ E = M + e * RADEG * sind(M) * (1.0 + e * cosd(M)); x = cosd(E) - e; y = sqrt(1.0 - e*e) * sind(E); *r = sqrt(x*x + y*y); /* Solar distance */ v = atan2d(y, x); /* True anomaly */ *lon = v + w; /* True solar longitude */ if (*lon >= 360.0) { *lon -= 360.0; /* Make it 0..360 degrees */ } } static void astro_sun_RA_dec(double d, double *RA, double *dec, double *r) { double lon, obl_ecl, x, y, z; /* Compute Sun's ecliptical coordinates */ astro_sunpos(d, &lon, r); /* Compute ecliptic rectangular coordinates (z=0) */ x = *r * cosd(lon); y = *r * sind(lon); /* Compute obliquity of ecliptic (inclination of Earth's axis) */ obl_ecl = 23.4393 - 3.563E-7 * d; /* Convert to equatorial rectangular coordinates - x is unchanged */ z = y * sind(obl_ecl); y = y * cosd(obl_ecl); /* Convert to spherical coordinates */ *RA = atan2d(y, x); *dec = atan2d(z, sqrt(x*x + y*y)); } /** * Note: timestamp = unixtimestamp (NEEDS to be 00:00:00 UT) * Eastern longitude positive, Western longitude negative * Northern latitude positive, Southern latitude negative * The longitude value IS critical in this function! * altit = the altitude which the Sun should cross * Set to -35/60 degrees for rise/set, -6 degrees * for civil, -12 degrees for nautical and -18 * degrees for astronomical twilight. * upper_limb: non-zero -> upper limb, zero -> center * Set to non-zero (e.g. 1) when computing rise/set * times, and to zero when computing start/end of * twilight. * *rise = where to store the rise time * *set = where to store the set time * Both times are relative to the specified altitude, * and thus this function can be used to compute * various twilight times, as well as rise/set times * Return value: 0 = sun rises/sets this day, times stored at * *trise and *tset. * +1 = sun above the specified "horizon" 24 hours. * *trise set to time when the sun is at south, * minus 12 hours while *tset is set to the south * time plus 12 hours. "Day" length = 24 hours * -1 = sun is below the specified "horizon" 24 hours * "Day" length = 0 hours, *trise and *tset are * both set to the time when the sun is at south. * */ int timelib_astro_rise_set_altitude(timelib_time *t_loc, double lon, double lat, double altit, int upper_limb, double *h_rise, double *h_set, timelib_sll *ts_rise, timelib_sll *ts_set, timelib_sll *ts_transit) { double d, /* Days since 2000 Jan 0.0 (negative before) */ sr, /* Solar distance, astronomical units */ sRA, /* Sun's Right Ascension */ sdec, /* Sun's declination */ sradius, /* Sun's apparent radius */ t, /* Diurnal arc */ tsouth, /* Time when Sun is at south */ sidtime; /* Local sidereal time */ timelib_time *t_utc; timelib_sll timestamp, old_sse; int rc = 0; /* Return cde from function - usually 0 */ /* Normalize time */ old_sse = t_loc->sse; t_loc->h = 12; t_loc->i = t_loc->s = 0; timelib_update_ts(t_loc, NULL); /* Calculate TS belonging to UTC 00:00 of the current day */ t_utc = timelib_time_ctor(); t_utc->y = t_loc->y; t_utc->m = t_loc->m; t_utc->d = t_loc->d; t_utc->h = t_utc->i = t_utc->s = 0; timelib_update_ts(t_utc, NULL); /* Compute d of 12h local mean solar time */ timestamp = t_loc->sse; d = timelib_ts_to_juliandate(timestamp) - lon/360.0; /* Compute local sidereal time of this moment */ sidtime = astro_revolution(astro_GMST0(d) + 180.0 + lon); /* Compute Sun's RA + Decl at this moment */ astro_sun_RA_dec( d, &sRA, &sdec, &sr ); /* Compute time when Sun is at south - in hours UT */ tsouth = 12.0 - astro_rev180(sidtime - sRA) / 15.0; /* Compute the Sun's apparent radius, degrees */ sradius = 0.2666 / sr; /* Do correction to upper limb, if necessary */ if (upper_limb) { altit -= sradius; } /* Compute the diurnal arc that the Sun traverses to reach */ /* the specified altitude altit: */ { double cost; cost = (sind(altit) - sind(lat) * sind(sdec)) / (cosd(lat) * cosd(sdec)); *ts_transit = t_utc->sse + (tsouth * 3600); if (cost >= 1.0) { rc = -1; t = 0.0; /* Sun always below altit */ *ts_rise = *ts_set = t_utc->sse + (tsouth * 3600); } else if (cost <= -1.0) { rc = +1; t = 12.0; /* Sun always above altit */ *ts_rise = t_loc->sse - (12 * 3600); *ts_set = t_loc->sse + (12 * 3600); } else { t = acosd(cost) / 15.0; /* The diurnal arc, hours */ /* Store rise and set times - as Unix Timestamp */ *ts_rise = ((tsouth - t) * 3600) + t_utc->sse; *ts_set = ((tsouth + t) * 3600) + t_utc->sse; *h_rise = (tsouth - t); *h_set = (tsouth + t); } } /* Kill temporary time and restore original sse */ timelib_time_dtor(t_utc); t_loc->sse = old_sse; return rc; } double timelib_ts_to_juliandate(timelib_sll ts) { double tmp; tmp = ts; tmp /= 86400; tmp += 2440587.5; tmp -= 2451543; return tmp; }