#!/usr/bin/env python3 # Copyright © 2014 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 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 <http://www.gnu.org/licenses/>. # This module implements algorithms for calculating information about the Sun. import math import time 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 ''' def sun(latitude, longitude, t = None, low = -6.0, high = 3.0): ''' Get the visibility of the Sun @param latitude:float The latitude component of your GPS coordinate @param longitude:float The longitude component of your GPS coordinate @param t:float? The time in Julian Centuries, `None` for current time @param low:float The 100 % night limit elevation of the Sun (highest when not visible) @param high:float The 100 % day limit elevation of the Sun (lowest while fully visible) @return :float The visibilty of the sun, 0 during the night, 1 during the day, between 0 and 1 during twilight. Other values will not occur. ''' t = julian_centuries() if t is None else t e = solar_elevation(latitude, longitude, t) e = (e - low) / (high - low) return min(max(0, e), 1) # 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 ''' 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 ''' 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 ''' 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 and TIME TRAVELERS: # 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 atleast the left operand. 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 ''' 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 ''' 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 ''' 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 ''' 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 ''' 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 degrees @param hour_angle:float The suns elevation, in degrees @return :float The solar hour angle, in degrees ''' 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 degrees @param hour_angle:float The solar hour angle, in degrees @return :float The suns elevation, in degrees ''' 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 seeked 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 seeked 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 degrees @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 Suns 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 suns apparent at the specified time as seen from the specified position, measured in degrees ''' 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 Suns 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 suns 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)