sun.py

# https://stackoverflow.com/a/39867990
import datetime
import math


class Sun:

    def getSunriseTime(self, coords):
        return self.calcSunTime(coords, True)

    def getSunsetTime(self, coords):
        return self.calcSunTime(coords, False)

    def getCurrentUTC(self):
        now = datetime.datetime.now()
        return [now.day, now.month, now.year]

    def calcSunTime(self, coords, isRiseTime, zenith=90.8):
        # isRiseTime == False, returns sunsetTime

        day, month, year = self.getCurrentUTC()

        longitude = coords['longitude']
        latitude = coords['latitude']

        TO_RAD = math.pi/180

        # 1. first calculate the day of the year
        N1 = math.floor(275 * month / 9)
        N2 = math.floor((month + 9) / 12)
        N3 = (1 + math.floor((year - 4 * math.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 isRiseTime:
            t = N + ((6 - lngHour) / 24)
        else:  # sunset
            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 * math.sin(TO_RAD*M)) + (0.020 * math.sin(TO_RAD * 2 * M)) + 282.634
        L = self.forceRange(L, 360)  # NOTE: L adjusted into the range [0,360)

        # 5a. calculate the Sun's right ascension

        RA = (1/TO_RAD) * math.atan(0.91764 * math.tan(TO_RAD*L))
        RA = self.forceRange(RA, 360)  # NOTE: RA adjusted into the range [0,360)

        # 5b. right ascension value needs to be in the same quadrant as L
        Lquadrant = (math.floor(L/90)) * 90
        RAquadrant = (math.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 * math.sin(TO_RAD*L)
        cosDec = math.cos(math.asin(sinDec))

        # 7a. calculate the Sun's local hour angle
        cosH = (math.cos(TO_RAD*zenith) - (sinDec * math.sin(TO_RAD*latitude))) \
            / (cosDec * math.cos(TO_RAD*latitude))

        if cosH > 1:
            return {
                'status': False,
                'msg': 'the sun never rises on this location (on the specified date)'
            }

        if cosH < -1:
            return {
                'status': False,
                'msg': 'the sun never sets on this location (on the specified date)'
            }

        # 7b. finish calculating H and convert into hours
        if isRiseTime:
            H = 360 - (1/TO_RAD) * math.acos(cosH)
        else:  # setting
            H = (1/TO_RAD) * math.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
        UT = self.forceRange(UT, 24)  # UTC time in decimal format (e.g. 23.23)

        # 10. Return
        hr = self.forceRange(int(UT), 24)
        min = round((UT - int(UT))*59, 0)

        return {
            'status': True,
            'decimal': UT,
            'hr': int(hr),
            'min': int(min)
        }

    def forceRange(self, v, max):
        # force v to be >= 0 and < max
        if v < 0:
            return v + max
        elif v >= max:
            return v - max

        return v