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cloudbase.mooo.com Git - z180-stamp.git/blob - time/daylight_seconds.c
2 * (C)2012 Michael Duane Rice All rights reserved.
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29 /* $Id: daylight_seconds.c 2369 2013-04-28 14:19:35Z swfltek $ */
32 Determine the amount of time the sun is above the horizon. At high latitudes, around the
33 solstices, this can be zero or greater than ONE_DAY.
40 extern long __latitude
;
43 daylight_seconds(const time_t * timer
)
48 /* convert latitude to radians */
49 l
= __latitude
/ 206264.806;
51 d
= -solar_declination(timer
);
53 /* partial 'Sunrise Equation' */
56 /* magnitude of d may exceed 1.0 at near solstices */
63 /* derive hour angle */
66 /* but for atmospheric refraction, this would be d /= M_PI */