Sunrise/Sunset Algorithm

1. first calculate the day of the year

N1 = floor(275 * month / 9) N2 = floor((month + 9) / 12) N3 = (1 + floor((year - 4 * floor(year / 4) + 2) / 3)) N = N1 - (N2 * N3) + day - 30

2. convert the longitude to hour value and calculate an approximate time

lngHour = longitude / 15

if rising time is desired: t = N + ((6 - lngHour) / 24) if setting time is desired: t = N + ((18 - lngHour) / 24)

3. calculate the Sun's mean anomaly

M = (0.9856 * t) - 3.289

4. calculate the Sun's true longitude

L = M + (1.916 * sin(M)) + (0.020 * sin(2 * M)) + 282.634 NOTE: L potentially needs to be adjusted into the range [0,360) by adding/subtracting 360

5a. calculate the Sun's right ascension

RA = atan(0.91764 * tan(L)) NOTE: RA potentially needs to be adjusted into the range [0,360) by adding/subtracting 360

5b. right ascension value needs to be in the same quadrant as L

Lquadrant = (floor( L/90)) * 90 RAquadrant = (floor(RA/90)) * 90 RA = RA + (Lquadrant - RAquadrant)

5c. right ascension value needs to be converted into hours

RA = RA / 15

6. calculate the Sun's declination

sinDec = 0.39782 * sin(L) cosDec = cos(asin(sinDec))

7a. calculate the Sun's local hour angle

cosH = (cos(zenith) - (sinDec * sin(latitude))) / (cosDec * cos(latitude))

if (cosH > 1) the sun never rises on this location (on the specified date) if (cosH < -1) the sun never sets on this location (on the specified date)

7b. finish calculating H and convert into hours

if if rising time is desired: H = 360 - acos(cosH) if setting time is desired: H = acos(cosH)

H = H / 15

8. calculate local mean time of rising/setting

T = H + RA - (0.06571 * t) - 6.622

9. adjust back to UTC

UT = T - lngHour NOTE: UT potentially needs to be adjusted into the range [0,24) by adding/subtracting 24

10. convert UT value to local time zone of latitude/longitude

localT = UT + localOffset