# solar-python — Solar data calculation and prediction library for Python # Copyright © 2014, 2015 Mattias Andrée (maandree@member.fsf.org) # # This program is free software: you can redistribute it and/or modify # it under the terms of the GNU Affero General Public License as published by # the Free Software Foundation, either version 3 of the License, or # (at your option) any later version. # # This program is distributed in the hope that it will be useful, # but WITHOUT ANY WARRANTY; without even the implied warranty of # MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the # GNU Affero General Public License for more details. # # You should have received a copy of the GNU Affero General Public License # along with this program. If not, see . SOLAR_APPARENT_RADIUS = 32 / 60 ''' :float Approximate apparent size of the Sun in degrees ''' SOLAR_ELEVATION_SUNSET_SUNRISE = 0.0 ''' :float The Sun's elevation at sunset and sunrise, measured in degrees ''' SOLAR_ELEVATION_CIVIL_DUSK_DAWN = -6.0 ''' :float The Sun's elevation at civil dusk and civil dawn, measured in degrees ''' SOLAR_ELEVATION_NAUTICAL_DUSK_DAWN = -12.0 ''' :float The Sun's elevation at nautical dusk and nautical dawn, measured in degrees ''' SOLAR_ELEVATION_ASTRONOMICAL_DUSK_DAWN = -18.0 ''' :float The Sun's elevation at astronomical dusk and astronomical dawn, measured in degrees ''' SOLAR_ELEVATION_RANGE_TWILIGHT = (-18.0, 0.0) ''' :(float, float) The Sun's lowest and highest elevation during all periods of twilight, measured in degrees ''' SOLAR_ELEVATION_RANGE_CIVIL_TWILIGHT = (-6.0, 0.0) ''' :(float, float) The Sun's lowest and highest elevation during civil twilight, measured in degrees ''' SOLAR_ELEVATION_RANGE_NAUTICAL_TWILIGHT = (-12.0, -6.0) ''' :(float, float) The Sun's lowest and highest elevation during nautical twilight, measured in degrees ''' SOLAR_ELEVATION_RANGE_ASTRONOMICAL_TWILIGHT = (-18.0, -12.0) ''' :(float, float) The Sun's lowest and highest elevation during astronomical twilight, measured in degrees ''' # The following functions are used to calculate the result for `sun` # (most of them) but could be used for anything else. There name is # should tell you enough, `t` (and `noon`) is in Julian Centuries # except for in the convertion methods. def julian_day_to_epoch(t): ''' Converts a Julian Day timestamp to a POSIX time timestamp @param t:float The time in Julian Days @return :float The time in POSIX time ''' return (t - 2440587.5) * 86400.0 def epoch_to_julian_day(t): ''' Converts a POSIX time timestamp to a Julian Day timestamp @param t:float The time in POSIX time @return :float The time in Julian Days ''' return t / 86400.0 + 2440587.5 def julian_day_to_julian_centuries(t): ''' Converts a Julian Day timestamp to a Julian Centuries timestamp @param t:float The time in Julian Days @return :float The time in Julian Centuries ''' return (t - 2451545.0) / 36525.0 def julian_centuries_to_julian_day(t): ''' Converts a Julian Centuries timestamp to a Julian Day timestamp @param t:float The time in Julian Centuries @return :float The time in Julian Days ''' return t * 36525.0 + 2451545.0 def epoch_to_julian_centuries(t): ''' Converts a POSIX time timestamp to a Julian Centuries timestamp @param t:float The time in POSIX time @return :float The time in Julian Centuries ''' return julian_day_to_julian_centuries(epoch_to_julian_day(t)) def julian_centuries_to_epoch(t): ''' Converts a Julian Centuries timestamp to a POSIX time timestamp @param t:float The time in Julian Centuries @return :float The time in POSIX time ''' return julian_day_to_epoch(julian_centuries_to_julian_day(t)) def epoch(): ''' Get current POSIX time @return :float The current POSIX time ''' import time return time.time() def julian_day(): ''' Get current Julian Day time @return :float The current Julian Day time ''' return epoch_to_julian_day(epoch()) def julian_centuries(): ''' Get current Julian Centuries time (100 Julian days since J2000) @return :float The current Julian Centuries time ''' return epoch_to_julian_centuries(epoch()) def radians(deg): ''' Convert an angle from degrees to radians @param deg:float The angle in degrees @return :float The angle in radians ''' import math return deg * math.pi / 180 def degrees(rad): ''' Convert an angle from radians to degrees @param rad:float The angle in radians @return :float The angle in degrees ''' import math return rad * 180 / math.pi def sun_geometric_mean_longitude(t): ''' Calculates the Sun's geometric mean longitude @param t:float The time in Julian Centuries @return :float The Sun's geometric mean longitude in radians ''' return radians((0.0003032 * t ** 2 + 36000.76983 * t + 280.46646) % 360) # CANNIBALISERS: # The result of this function should always be positive, this # means that after division modulo 360 but before `radians`, # you will need to add 360 if the value is negative. This can # only happen if `t` is negative, which can only happen for date # times before 2000-(01)Jan-01 12:00:00 UTC par division modulo # implementations with the signess of at least the left operand. # More precively, it happens between circa 1970-(01)Jan-11 # 16:09:02 UTC and circa 374702470660351740 seconds before # January 1, 1970 00:00 UTC, which is so far back in time # it cannot be reliable pinned down to the right year, but it # is without a shadow of a doubt looooong before the Earth # was formed, is right up there with the age of the Milky Way # and the universe itself. def sun_geometric_mean_anomaly(t): ''' Calculates the Sun's geometric mean anomaly @param t:float The time in Julian Centuries @return :float The Sun's geometric mean anomaly in radians ''' return radians(-0.0001537 * t ** 2 + 35999.05029 * t + 357.52911) def earth_orbit_eccentricity(t): ''' Calculates the Earth's orbit eccentricity @param t:float The time in Julian Centuries @return :float The Earth's orbit eccentricity ''' return -0.0000001267 * t ** 2 - 0.000042037 * t + 0.016708634 def sun_equation_of_centre(t): ''' Calculates the Sun's equation of the centre, the difference between the true anomaly and the mean anomaly @param t:float The time in Julian Centuries @return :float The Sun's equation of the centre, in radians ''' import math a = sun_geometric_mean_anomaly(t) rc = math.sin(1 * a) * (-0.000014 * t ** 2 - 0.004817 * t + 1.914602) rc += math.sin(2 * a) * (-0.000101 * t + 0.019993) rc += math.sin(3 * a) * 0.000289 return radians(rc) def sun_real_longitude(t): ''' Calculates the Sun's real longitudinal position @param t:float The time in Julian Centuries @return :float The longitude, in radians ''' rc = sun_geometric_mean_longitude(t) return rc + sun_equation_of_centre(t) def sun_apparent_longitude(t): ''' Calculates the Sun's apparent longitudinal position @param t:float The time in Julian Centuries @return :float The longitude, in radians ''' import math rc = degrees(sun_real_longitude(t)) - 0.00569 rc -= 0.00478 * math.sin(radians(-1934.136 * t + 125.04)) return radians(rc) def mean_ecliptic_obliquity(t): ''' Calculates the mean ecliptic obliquity of the Sun's apparent motion without variation correction @param t:float The time in Julian Centuries @return :float The uncorrected mean obliquity, in radians ''' rc = 0.001813 * t ** 3 - 0.00059 * t ** 2 - 46.815 * t + 21.448 rc = 26 + rc / 60 rc = 23 + rc / 60 return radians(rc) def corrected_mean_ecliptic_obliquity(t): ''' Calculates the mean ecliptic obliquity of the Sun's apparent motion with variation correction @param t:float The time in Julian Centuries @return :float The mean obliquity, in radians ''' import math rc = -1934.136 * t + 125.04 rc = 0.00256 * math.cos(radians(rc)) rc += degrees(mean_ecliptic_obliquity(t)) return radians(rc) def solar_declination(t): ''' Calculates the Sun's declination @param t:float The time in Julian Centuries @return :float The Sun's declination, in radians ''' import math rc = math.sin(corrected_mean_ecliptic_obliquity(t)) rc *= math.sin(sun_apparent_longitude(t)) return math.asin(rc) def equation_of_time(t): ''' Calculates the equation of time, the discrepancy between apparent and mean solar time @param t:float The time in Julian Centuries @return :float The equation of time, in degrees ''' import math l = sun_geometric_mean_longitude(t) e = earth_orbit_eccentricity(t) m = sun_geometric_mean_anomaly(t) y = corrected_mean_ecliptic_obliquity(t) y = math.tan(y / 2) ** 2 rc = y * math.sin(2 * l) rc += (4 * y * math.cos(2 * l) - 2) * e * math.sin(m) rc -= 0.5 * y ** 2 * math.sin(4 * l) rc -= 1.25 * e ** 2 * math.sin(2 * m) return 4 * degrees(rc) def hour_angle_from_elevation(latitude, declination, elevation): ''' Calculates the solar hour angle from the Sun's elevation @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param declination:float The declination, in radians @param elevation:float The Sun's elevation, in radians @return :float The solar hour angle, in radians ''' import math if elevation == 0: return 0 rc = math.cos(abs(elevation)) rc -= math.sin(radians(latitude)) * math.sin(declination) rc /= math.cos(radians(latitude)) * math.cos(declination) rc = math.acos(rc) return -rc if (rc < 0) == (elevation < 0) else rc; def elevation_from_hour_angle(latitude, declination, hour_angle): ''' Calculates the Sun's elevation from the solar hour angle @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param declination:float The declination, in radians @param hour_angle:float The solar hour angle, in radians @return :float The Sun's elevation, in radians ''' import math rc = math.cos(radians(latitude)) rc *= math.cos(hour_angle) * math.cos(declination) rc += math.sin(radians(latitude)) * math.sin(declination) return math.asin(rc) def time_of_solar_noon(t, longitude): ''' Calculates the time of the closest solar noon @param t:float A time close to the sought time, in Julian Centuries @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @return :float The time, in Julian Centuries, of the closest solar noon ''' t, rc = julian_centuries_to_julian_day(t), longitude for (k, m) in ((-360, 0), (1440, -0.5)): rc = julian_day_to_julian_centuries(t + m + rc / k) rc = 720 - 4 * longitude - equation_of_time(rc) return rc def time_of_solar_elevation(t, noon, latitude, longitude, elevation): ''' Calculates the time the Sun has a specified apparent elevation at a geographical position @param t:float A time close to the sought time, in Julian Centuries @param noon:float The time of the closest solar noon @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param elevation:float The solar elevation, in radians @return :float The time, in Julian Centuries, of the specified elevation ''' rc = noon rc, et = solar_declination(rc), equation_of_time(rc) rc = hour_angle_from_elevation(latitude, rc, elevation) rc = 720 - 4 * (longitude + degrees(rc)) - et rc = julian_day_to_julian_centuries(julian_centuries_to_julian_day(t) + rc / 1440) rc, et = solar_declination(rc), equation_of_time(rc) rc = hour_angle_from_elevation(latitude, rc, elevation) rc = 720 - 4 * (longitude + degrees(rc)) - et return rc def solar_elevation_from_time(t, latitude, longitude): ''' Calculates the Sun's elevation as apparent from a geographical position @param t:float The time in Julian Centuries @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @return :float The Sun's apparent at the specified time as seen from the specified position, measured in radians ''' rc = julian_centuries_to_julian_day(t) rc = (rc - float(int(rc + 0.5)) - 0.5) * 1440 rc = 720 - rc - equation_of_time(t) rc = radians(rc / 4 - longitude) return elevation_from_hour_angle(latitude, solar_declination(t), rc) def solar_elevation(latitude, longitude, t = None): ''' Calculates the Sun's elevation as apparent from a geographical position @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param t:float? The time in Julian Centuries, `None` for the current time @return :float The Sun's apparent at the specified time as seen from the specified position, measured in degrees ''' rc = julian_centuries() if t is None else t rc = solar_elevation_from_time(rc, latitude, longitude) return degrees(rc) def have_sunrise_and_sunset(latitude, t = None): ''' Determine whether solar declination currently is so that there can be sunrises and sunsets. If not, you either have 24-hour daytime or 24-hour nighttime. @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param t:float? The time in Julian Centuries, `None` for the current time @return Whether there can be sunrises and sunsets where you are located ''' t = julian_centuries() if t is None else t d = degrees(solar_declination(t)) ## Convert everything to the Northern hemisphere latitude = abs(latitude) if d >= 0: ## Northern summer return -90 + d < latitude < 90 - d else: ## Northern winter return -90 - d < latitude < 90 + d def is_summer(latitude, t = None): ''' Determine whether it is summer @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param t:float? The time in Julian Centuries, `None` for the current time @return Whether it is summer on the hemisphere you are located on ''' t = julian_centuries() if t is None else t d = solar_declination(t) return (d > 0) == (latitude > 0) def is_winter(latitude, t = None): ''' Determine whether it is winter @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param t:float? The time in Julian Centuries, `None` for the current time @return Whether it is winter on the hemisphere you are located on ''' t = julian_centuries() if t is None else t d = solar_declination(t) return not ((d > 0) == (latitude > 0)) def solar_prediction(delta, requested, fun, epsilon = 0.000001, span = 0.01, t = None): ''' Predict the time point of the next or previous time an arbitrary condition is meet @param delta:float Iteration step size, negative for past event, positive for future event @param requested:float The value returned by `fun` for which to calculate the time point of occurrence @param fun:(t:float)→float Function that calculate the data of interest @param epsilon:float Error tolerance for `requested` @param span:float The number of Julian Centuries (0,01 for one year) to restrict the search to @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within the specified time span ''' fun_ = lambda t : fun(t) - requested t = julian_centuries() if t is None else t t1 = t2 = t v1 = v0 = fun_(t) # Predicate time point to within a small time span while True: if abs(t2 - t) > span: return None t2 += delta v2 = fun_(t2) if (v1 <= 0 <= v2) or ((0 >= v1 >= v2) and (0 <= v0)): break if (v1 >= 0 >= v2) or ((0 <= v1 <= v2) and (0 >= v0)): break t1 = t2 v2 = v1 # Binary search the small time span for the exact time point for _itr in range(1000): tm = (t1 + t2) / 2 v1 = fun_(t1) v2 = fun_(t2) vm = fun_(tm) if abs(v1 - v2) < epsilon: return tm if abs(vm) < epsilon else None if v1 < v2: if 0 < vm: t2 = tm else: t1 = tm elif v1 > v2: if 0 > vm: t2 = tm else: t1 = tm return None def future_past_equinox(delta, t = None): ''' Predict the time point of the next or previous equinox @param delta:float Iteration step size, negative for past event, positive for future event @param t:float? The time in Julian Centuries, `None` for the current time @return :float The calculated time point ''' return solar_prediction(delta, 0, solar_declination, t = t) def future_equinox(t = None): ''' Predict the time point of the next equinox @param t:float? The time in Julian Centuries, `None` for the current time @return :float The calculated time point ''' return future_past_equinox(0.01 / 2000, t) def past_equinox(t = None): ''' Predict the time point of the previous equinox @param t:float? The time in Julian Centuries, `None` for the current time @return :float The calculated time point ''' return future_past_equinox(0.01 / -2000, t) def future_past_solstice(delta, t = None): ''' Predict the time point of the next or previous solstice @param delta:float Iteration step size, negative for past event, positive for future event @param t:float? The time in Julian Centuries, `None` for the current time @return :float The calculated time point ''' e = 0.00001 fun = solar_declination dfun = lambda t : (fun(t + e) - fun(t - e)) / (2 * e) return solar_prediction(delta, 0, dfun, t = t) def future_solstice(t = None): ''' Predict the time point of the next solstice @param t:float? The time in Julian Centuries, `None` for the current time @return :float The calculated time point ''' return future_past_solstice(0.01 / 2000, t) def past_solstice(t = None): ''' Predict the time point of the previous solstice @param t:float? The time in Julian Centuries, `None` for the current time @return :float The calculated time point ''' return future_past_solstice(0.01 / -2000, t) def future_past_elevation(delta, latitude, longitude, elevation, t = None): ''' Predict the time point of the next or previous time the Sun reaches or reached a specific elevation @param delta:float Iteration step size, negative for past event, positive for future event @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param elevation:float The elevation of interest @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within a year ''' fun = lambda t : solar_elevation(latitude, longitude, t) return solar_prediction(delta, elevation, fun, t = t) def future_elevation(latitude, longitude, elevation, t = None): ''' Predict the time point of the next time the Sun reaches a specific elevation @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param elevation:float The elevation of interest @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within a year ''' return future_past_elevation(0.01 / 2000, latitude, longitude, elevation, t) def past_elevation(latitude, longitude, elevation, t = None): ''' Predict the time point of the previous time the Sun reached a specific elevation @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param elevation:float The elevation of interest @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within a year ''' return future_past_elevation(0.01 / -2000, latitude, longitude, elevation, t) def future_past_elevation_derivative(delta, latitude, longitude, derivative, t = None): ''' Predict the time point of the next or previous time the Sun reaches or reached a specific elevation derivative @param delta:float Iteration step size, negative for past event, positive for future event @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param derivative:float The elevation derivative value of interest @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within a year ''' e = 0.00001 fun = lambda t : solar_elevation(latitude, longitude, t) dfun = lambda t : (fun(t + e) - fun(t - e)) / (2 * e) return solar_prediction(delta, derivative, dfun, t = t) def future_elevation_derivative(latitude, longitude, derivative, t = None): ''' Predict the time point of the next time the Sun reaches a specific elevation derivative @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param derivative:float The elevation derivative value of interest @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within a year ''' return future_past_elevation_derivative(0.01 / 2000, latitude, longitude, derivative, t) def past_elevation_derivative(latitude, longitude, derivative, t = None): ''' Predict the time point of the previous time the Sun reached a specific elevation derivative @param latitude:float The latitude in degrees northwards from the equator, negative for southwards @param longitude:float The longitude in degrees eastwards from Greenwich, negative for westwards @param derivative:float The elevation derivative value of interest @param t:float? The time in Julian Centuries, `None` for the current time @return :float? The calculated time point, `None` if none were found within a year ''' return future_past_elevation_derivative(0.01 / -2000, latitude, longitude, derivative, t) # TODO: This algorithm is imprecise, gives an incorrent sunrise and I do not fully know its behaviour def sunrise_equation(latitude, longitude, t = None): import math # Calculate Julian Cycle j_cent = julian_centuries() if t is None else t j_date = julian_centuries_to_julian_day(j_cent) j_cycle = int(j_date - 2451545.0009 - longitude / 360 + 0.5) # Calculate approximate solar noon and solar man anomaly approx_solar_noon = 451545.0009 + longitude / 360 + j_cycle solar_mean_anomaly = int(357.5291 + 0.98560028 * (j_cycle - 2451545)) % 360 # Calculate solar equation of centre equation_of_centre = 1.9148 * sin(1 * solar_mean_anomaly) equation_of_centre += 0.0200 * sin(2 * solar_mean_anomaly) equation_of_centre += 0.0003 * sin(3 * solar_mean_anomaly) # Calculate solar ecliptic longitude ecliptic_longitude = (solar_mean_anomaly + 102.9372 + equation_of_centre + 180) % 360 # Calculate solar transit solar_transit = approx_solar_noon + 0.0053 * math.sin(solar_mean_anomaly) solar_transit -= 0.0069 * math.sin(2 * ecliptic_longitude) # Calculate solar declination declination = math.asin(math.sin(ecliptic_longitude) * math.sin(radians(23.45))) # Calculate solar hour angle hour_angle = math.sin(radians(-0.83)) hour_angle -= math.sin(latitude) * math.sin(declination) hour_angle /= math.cos(latitude) * math.cos(declination) hour_angle = degrees(math.acos(hour_angle)) # Calculate time of sunset and sunrise sunset = 2451545.0009 + (hour_angle + longitude) / 360 sunset += j_cycle + solar_transit - approx_solar_noon sunrise = 2 * solar_transit - sunset # Convert to Julian Centuries return (julian_day_to_julian_centuries(sunset), julian_day_to_julian_centuries(sunrise))