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sunriset.h
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/* +++Date last modified: 05-Jul-1997 */
/* Updated comments, 05-Aug-2013 */
/*
SUNRISET.C - computes Sun rise/set times, start/end of twilight, and
the length of the day at any date and latitude
Written as DAYLEN.C, 1989-08-16
Modified to SUNRISET.C, 1992-12-01
(c) Paul Schlyter, 1989, 1992
Released to the public domain by Paul Schlyter, December 1992
*/
/* A macro to compute the number of days elapsed since 2000 Jan 0.0 */
/* (which is equal to 1999 Dec 31, 0h UT) */
#define days_since_2000_Jan_0(y,m,d) \
(367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L)
/* Some conversion factors between radians and degrees */
#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. */
/* This macro 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). */
#define day_length(year,month,day,lon,lat) \
__daylen__( year, month, day, lon, lat, -35.0/60.0, 1 )
/* This macro computes the length of the day, including civil twilight. */
/* Civil twilight starts/ends when the Sun's center is 6 degrees below */
/* the horizon. */
#define day_civil_twilight_length(year,month,day,lon,lat) \
__daylen__( year, month, day, lon, lat, -6.0, 0 )
/* This macro computes the length of the day, incl. nautical twilight. */
/* Nautical twilight starts/ends when the Sun's center is 12 degrees */
/* below the horizon. */
#define day_nautical_twilight_length(year,month,day,lon,lat) \
__daylen__( year, month, day, lon, lat, -12.0, 0 )
/* This macro computes the length of the day, incl. astronomical twilight. */
/* Astronomical twilight starts/ends when the Sun's center is 18 degrees */
/* below the horizon. */
#define day_astronomical_twilight_length(year,month,day,lon,lat) \
__daylen__( year, month, day, lon, lat, -18.0, 0 )
/* This macro 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). */
#define sun_rise_set(year,month,day,lon,lat,rise,set) \
__sunriset__( year, month, day, lon, lat, -35.0/60.0, 1, rise, set )
/* This macro computes the start and end times of civil twilight. */
/* Civil twilight starts/ends when the Sun's center is 6 degrees below */
/* the horizon. */
#define civil_twilight(year,month,day,lon,lat,start,end) \
__sunriset__( year, month, day, lon, lat, -6.0, 0, start, end )
/* This macro computes the start and end times of nautical twilight. */
/* Nautical twilight starts/ends when the Sun's center is 12 degrees */
/* below the horizon. */
#define nautical_twilight(year,month,day,lon,lat,start,end) \
__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. */
#define astronomical_twilight(year,month,day,lon,lat,start,end) \
__sunriset__( year, month, day, lon, lat, -18.0, 0, start, end )
/* Function prototypes */
double __daylen__( int year, int month, int day, double lon, double lat,
double altit, int upper_limb );
int __sunriset__( int year, int month, int day, double lon, double lat,
double altit, int upper_limb, double *rise, double *set );
void sunpos( double d, double *lon, double *r );
void sun_RA_dec( double d, double *RA, double *dec, double *r );
double revolution( double x );
double rev180( double x );
double GMST0( double d );