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<? /* sunriset.inc (c) Brian Leyton 10/28/98 May be used freely for commercial or non-commercial use, as long as this notice is not removed. Any comments may be sent to bleyton@bigfoot.com. Adapted from SUNRISET.C by Paul Schlyter 05-Jul-1997 */ /* A function to compute the number of days elapsed since 2000 Jan 0.0 */ /* (which is equal to 1999 Dec 31, 0h UT) */ function days_since_2000_Jan_0($y,$m,$d) { $days = (int) (367*($y)-((7*(($y)+((($m)+9)/12)))/4)+((275*($m))/9)+($d)- 730530); return $days; } /* Some conversion factors between radians and degrees */ define("PI",3.1415926535897932384); define("RADEG",( 180.0 / PI )); define("DEGRAD",( PI / 180.0 )); define("INV360",( 1.0 / 360.0 )); /* The trigonometric functions in degrees */ function sind($x) { $res = (double) sin(($x)*DEGRAD); return $res; } function cosd($x) { $res = (double) cos(($x)*DEGRAD); return $res; } function tand($x) { $res = (double) tan(($x)*DEGRAD); return $res; } function atand($x) { $res = (double) RADEG*atan($x); return $res; } function asind($x) { $res = (double) RADEG*asin($x); return $res; } function acosd($x) { $res = (double) RADEG*acos($x); return $res; } /* If you're running an early version of PHP, which doesn't have this function built-in, just un-comment the following code function atan2($x,$y) { if($x > 0) $res = atan($y/$x); elseif($x < 0) $res = atan($y/$x) + PI; /* below $x is zero elseif($y > 0) $res = PI/2; elseif($y < 0) $res = -PI/2; /* Below, both $x and $y are 0 else $res = 0; return $res; }*/ function atan2d($y,$x) { $res = (double) RADEG*atan2($y,$x); return $res; } function sun_RA_dec( $d, &$RA, &$dec, &$r ) { $lon = (double) 0; $obl_ecl = (double) 0; $x = (double) 0; $y = (double) 0; $z = (double) 0; /* Compute Sun's ecliptical coordinates */ 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) ); } /* sun_RA_dec */ /******************************************************************/ /* 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 */ /******************************************************************/ function revolution( $x ) /*****************************************/ /* Reduce angle to within 0..360 degrees */ /*****************************************/ { return( $x - 360.0 * floor( $x * INV360 ) ); } /* revolution */ function rev180( $x ) /*********************************************/ /* Reduce angle to within +180..+180 degrees */ /*********************************************/ { return( $x - 360.0 * floor( $x * INV360 + 0.5 ) ); } /* rev180 */ /*******************************************************************/ /* 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) */ /* */ /*******************************************************************/ function GMST0( $d ) { $sidtim0 = (double) 0; /* 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 = revolution( ( 180.0 + 356.0470 + 282.9404 ) + ( 0.9856002585 + 4.70935E-5 ) * $d ); return $sidtim0; } /* GMST0 */ /* The "workhorse" function for sun rise/set times */ function sunriset( $year, $month, $day, $lon, $lat, $altit, $upper_limb, & $trise, &$tset) /***************************************************************************/ /* Note: year,month,date = calendar date, 1801-2099 only. */ /* 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. */ /* */ /**********************************************************************/ { $d = (double) 0; /* Days since 2000 Jan 0.0 (negative before) */ $sr = (double) 0; /* Solar distance, astronomical units */ $sRA = (double) 0; /* Sun's Right Ascension */ $sdec = (double) 0; /* Sun's declination */ $sradius = (double) 0; /* Sun's apparent radius */ $t = (double) 0; /* Diurnal arc */ $tsouth = (double) 0; /* Time when Sun is at south */ $sidtime = (double) 0; /* Local sidereal time */ $rc = (int) 0; /* Return cde from function - usually 0 */ /* Compute d of 12h local mean solar time */ $d = (double) days_since_2000_Jan_0($year,$month,$day) + 0.5 - $lon/360.0; /* Compute local sidereal time of this moment */ $sidtime = (double) revolution( GMST0($d) + 180.0 + $lon ); /* Compute Sun's RA + Decl at this moment */ sun_RA_dec( $d, &$sRA, &$sdec, &$sr ); /* Compute time when Sun is at south - in hours UT */ $tsouth = 12.0 - rev180($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: */ { $cost = (double) ( sind($altit) - sind($lat) * sind($sdec) ) / ( cosd($lat) * cosd($sdec) ); if ( $cost >= 1.0 ) { $rc = -1; $t = 0.0; /* Sun always below altit */ } elseif ( $cost <= -1.0 ) { $rc = +1; $t = 12.0; /* Sun always above altit */ } else $t = acosd($cost)/15.0; /* The diurnal arc, hours */ } /* Store rise and set times - in hours UT */ $trise = $tsouth - $t; $tset = $tsouth + $t; return $rc; } /* __sunriset__ */ /* This function computes the Sun's position at any instant */ function sunpos( $d, &$lon, &$r ) /******************************************************/ /* 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. */ /******************************************************/ { $M = (double) 0; /* Mean anomaly of the Sun */ $w = (double) 0; /* Mean longitude of perihelion */ /* Note: Sun's mean longitude = M + w */ $e = (double) 0; /* Eccentricity of Earth's orbit */ $ea = (double) 0; /* Eccentric anomaly */ $x = (double) 0; $y = (double) 0; /* x, y coordinates in orbit */ $v = (double) 0; /* True anomaly */ /* Compute mean elements */ $M = 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 */ $ea = $M + $e * RADEG * sind($M) * ( 1.0 + $e * cosd($M) ); $x = cosd($ea) - $e; $y = sqrt( 1.0 - $e*$e ) * sind($ea); $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 */ } /* The "workhorse" function for day length */ function daylen( $year, $month, $day, $lon, $lat, $altit, $upper_limb ) /**********************************************************************/ /* Note: year,month,date = calendar date, 1801-2099 only. */ /* Eastern longitude positive, Western longitude negative */ /* Northern latitude positive, Southern latitude negative */ /* The longitude value is not critical. Set it to the correct */ /* longitude if you're picky, otherwise set to to, say, 0.0 */ /* The latitude however IS critical - be sure to get it correct */ /* 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 day length */ /* and to zero when computing day+twilight length. */ /**********************************************************************/ { $d = (double) 0; /* Days since 2000 Jan 0.0 (negative before) */ $obl_ecl = (double) 0; /* Obliquity (inclination) of Earth's axis */ $sr = (double) 0; /* Solar distance, astronomical units */ $slon = (double) 0; /* True solar longitude */ $sin_sdecl = (double) 0; /* Sine of Sun's declination */ $cos_sdecl = (double) 0; /* Cosine of Sun's declination */ $sradius = (double) 0; /* Sun's apparent radius */ $t = (double) 0; /* Diurnal arc */ /* Compute d of 12h local mean solar time */ $d = days_since_2000_Jan_0($year,$month,$day) + 0.5 - $lon/360.0; /* Compute obliquity of ecliptic (inclination of Earth's axis) */ $obl_ecl = 23.4393 - 3.563E-7 * $d; /* Compute Sun's position */ sunpos( $d, &$slon, &$sr ); /* Compute sine and cosine of Sun's declination */ $sin_sdecl = sind($obl_ecl) * sind($slon); $cos_sdecl = sqrt( 1.0 - $sin_sdecl * $sin_sdecl ); /* 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: */ { $cost = (double)( sind($altit) - sind($lat) * $sin_sdecl ) / ( cosd($lat) * $cos_sdecl ); if ( $cost >= 1.0 ) $t = 0.0; /* Sun always below altit */ else if ( $cost <= -1.0 ) $t = 24.0; /* Sun always above altit */ else $t = (2.0/15.0) * acosd($cost); /* The diurnal arc, hours */ } return $t; } /* __daylen__ */ /* Following are some functions around the "workhorse" function "daylen" */ /* They mainly fill in the desired values for the reference altitude */ /* below the horizon, and also selects whether this altitude should */ /* refer to the Sun's center or its upper limb. */ /* This function computes the length of the day, from sunrise to sunset. */ /* Sunrise/set is considered to occur when the Sun's upper limb is */ /* 35 arc minutes below the horizon (this accounts for the refraction */ /* of the Earth's atmosphere). */ function day_length($year,$month,$day,$lon,$lat) { $res=daylen( $year, $month, $day, $lon, $lat, -35.0/60.0, 1 ); return $res; } /* This function computes the length of the day, including civil twilight. */ /* Civil twilight starts/ends when the Sun's center is 6 degrees below */ /* the horizon. */ function day_civil_twilight_length($year,$month,$day,$lon,$lat) { $res = daylen( $year, $month, $day, $lon, $lat, -6.0, 0 ); return $res; } /* This function computes the length of the day, incl. nautical twilight. */ /* Nautical twilight starts/ends when the Sun's center is 12 degrees */ /* below the horizon. */ function day_nautical_twilight_length($year,$month,$day,$lon,$lat) { $res = daylen( $year, $month, $day, $lon, $lat, -12.0, 0 ); return $res; } /* This function computes the length of the day, incl. astronomical */ /* twilight. Astronomical twilight starts/ends when the Sun's center is */ /* 18 degrees below the horizon. */ function day_astronomical_twilight_length($year,$month,$day,$lon,$lat) { $res = daylen( $year, $month, $day, $lon, $lat, -18.0, 0 ); return $res; } /* This function computes times for sunrise/sunset. */ /* Sunrise/set is considered to occur when the Sun's upper limb is */ /* 35 arc minutes below the horizon (this accounts for the refraction */ /* of the Earth's atmosphere). */ function sun_rise_set($year,$month,$day,$lon,$lat,$rise,$set) { $res = sunriset($year,$month,$day,$lon,$lat, -35.0/60.0, 1,$rise,$set ); return $res; } /* This function computes the start and end times of civil twilight. */ /* Civil twilight starts/ends when the Sun's center is 6 degrees below */ /* the horizon. */ function civil_twilight($year,$month,$day,$lon,$lat,$start,$end) { $res = sunriset( $year, $month, $day, $lon, $lat, -6.0, 0, $start, $end ); return $res; } /* This function computes the start and end times of nautical twilight. */ /* Nautical twilight starts/ends when the Sun's center is 12 degrees */ /* below the horizon. */ function nautical_twilight($year,$month,$day,$lon,$lat,$start,$end) { $res = sunriset( $year, $month, $day, $lon, $lat, -12.0, 0, $start, $end ); } /* This macro computes the start and end times of astronomical twilight. */ /* Astronomical twilight starts/ends when the Sun's center is 18 degrees */ /* below the horizon. */ function astronomical_twilight($year,$month,$day,$lon,$lat,$start,$end) { $res = sunriset( $year, $month, $day, $lon, $lat, -18.0, 0, $start, $end ); return $res; } ?> | ||||||||||
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