# Sun.py

Apr 19th, 2021 (edited)
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1. # -*- coding: iso-8859-1 -*-
2. """
3. SUNRISET.C - computes Sun rise/set times, start/end of twilight, and
4.             the length of the day at any date and latitude
5.
6. Written as DAYLEN.C, 1989-08-16
7.
8. Modified to SUNRISET.C, 1992-12-01
9.
10. (c) Paul Schlyter, 1989, 1992
11.
12. Released to the public domain by Paul Schlyter, December 1992
13.
14. Direct conversion to Java
15. Sean Russell <ser@germane-software.com>
16.
17. Conversion to Python Class, 2002-03-21
19.
20. Solar Altitude added by Miguel Tremblay 2005-01-16
21. Solar flux, equation of time and import of python library
22.  added by Miguel Tremblay 2007-11-22
23.
24.
25. 2007-12-12 - v1.5 by Miguel Tremblay: bug fix to solar flux calculation
26.
27.
28. """
29.
30. SUN_PY_VERSION = 1.5
31.
32. import math
33. from math import pi
34.
35. import calendar
36.
37. class Sun:
38.
39.     def __init__(self):
40.         """"""
41.
42.         # Some conversion factors between radians and degrees
43.         self.RADEG = 180.0 / pi
44.         self.DEGRAD = pi / 180.0
45.         self.INV360 = 1.0 / 360.0
46.
47.
48.     def daysSince2000Jan0(self, y, m, d):
49.         """A macro to compute the number of days elapsed since 2000 Jan 0.0
50.           (which is equal to 1999 Dec 31, 0h UT)"""
51.         return (367*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530)
52.
53.
54.     # The trigonometric functions in degrees
55.     def sind(self, x):
56.         """Returns the sin in degrees"""
58.
59.     def cosd(self, x):
60.         """Returns the cos in degrees"""
62.
63.     def tand(self, x):
64.         """Returns the tan in degrees"""
66.
67.     def atand(self, x):
68.         """Returns the arc tan in degrees"""
70.
71.     def asind(self, x):
72.         """Returns the arc sin in degrees"""
74.
75.     def acosd(self, x):
76.         """Returns the arc cos in degrees"""
78.
79.     def atan2d(self, y, x):
80.         """Returns the atan2 in degrees"""
81.         return math.atan2(y, x) * self.RADEG
82.
83.     # Following are some macros around the "workhorse" function __daylen__
84.     # They mainly fill in the desired values for the reference altitude
85.     # below the horizon, and also selects whether this altitude should
86.     # refer to the Sun's center or its upper limb.
87.
88.     def dayLength(self, year, month, day, lon, lat):
89.         """
90.        This macro computes the length of the day, from sunrise to sunset.
91.        Sunrise/set is considered to occur when the Sun's upper limb is
92.        35 arc minutes below the horizon (this accounts for the refraction
93.        of the Earth's atmosphere).
94.        """
95.         return self.__daylen__(year, month, day, lon, lat, -35.0/60.0, 1)
96.
97.     def dayCivilTwilightLength(self, year, month, day, lon, lat):
98.         """
99.        This macro computes the length of the day, including civil twilight.
100.        Civil twilight starts/ends when the Sun's center is 6 degrees below
101.        the horizon.
102.        """
103.         return self.__daylen__(year, month, day, lon, lat, -6.0, 0)
104.
105.     def dayNauticalTwilightLength(self, year, month, day, lon, lat):
106.         """
107.        This macro computes the length of the day, incl. nautical twilight.
108.        Nautical twilight starts/ends when the Sun's center is 12 degrees
109.        below the horizon.
110.        """
111.         return self.__daylen__(year, month, day, lon, lat, -12.0, 0)
112.
113.     def dayAstronomicalTwilightLength(self, year, month, day, lon, lat):
114.         """
115.        This macro computes the length of the day, incl. astronomical twilight.
116.        Astronomical twilight starts/ends when the Sun's center is 18 degrees
117.        below the horizon.
118.        """
119.         return self.__daylen__(year, month, day, lon, lat, -18.0, 0)
120.
121.     def sunRiseSet(self, year, month, day, lon, lat):
122.         """
123.        This macro computes times for sunrise/sunset.
124.        Sunrise/set is considered to occur when the Sun's upper limb is
125.        35 arc minutes below the horizon (this accounts for the refraction
126.        of the Earth's atmosphere).
127.        """
128.         return self.__sunriset__(year, month, day, lon, lat, -35.0/60.0, 1)
129.
130.
131.     def civilTwilight(self, year, month, day, lon, lat):
132.         """
133.        This macro computes the start and end times of civil twilight.
134.        Civil twilight starts/ends when the Sun's center is 6 degrees below
135.        the horizon.
136.        """
137.         return self.__sunriset__(year, month, day, lon, lat, -6.0, 0)
138.
139.     def nauticalTwilight(self, year, month, day, lon, lat):
140.         """
141.        This macro computes the start and end times of nautical twilight.
142.        Nautical twilight starts/ends when the Sun's center is 12 degrees
143.        below the horizon.
144.        """
145.         return self.__sunriset__(year, month, day, lon, lat, -12.0, 0)
146.
147.     def astronomicalTwilight(self, year, month, day, lon, lat):
148.         """
149.        This macro computes the start and end times of astronomical twilight.
150.        Astronomical twilight starts/ends when the Sun's center is 18 degrees
151.        below the horizon.
152.        """
153.         return self.__sunriset__(year, month, day, lon, lat, -18.0, 0)
154.
155.     # The "workhorse" function for sun rise/set times
156.     def __sunriset__(self, year, month, day, lon, lat, altit, upper_limb):
157.         """
158.        Note: year,month,date = calendar date, 1801-2099 only.
159.              Eastern longitude positive, Western longitude negative
160.              Northern latitude positive, Southern latitude negative
161.              The longitude value IS critical in this function!
162.              altit = the altitude which the Sun should cross
163.                      Set to -35/60 degrees for rise/set, -6 degrees
164.                      for civil, -12 degrees for nautical and -18
165.                      degrees for astronomical twilight.
166.                upper_limb: non-zero -> upper limb, zero -> center
167.                      Set to non-zero (e.g. 1) when computing rise/set
168.                      times, and to zero when computing start/end of
169.                      twilight.
170.              *rise = where to store the rise time
171.              *set  = where to store the set  time
172.                      Both times are relative to the specified altitude,
173.                      and thus this function can be used to compute
174.                      various twilight times, as well as rise/set times
175.        Return value:  0 = sun rises/sets this day, times stored at
176.                           *trise and *tset.
177.                      +1 = sun above the specified 'horizon' 24 hours.
178.                           *trise set to time when the sun is at south,
179.                           minus 12 hours while *tset is set to the south
180.                           time plus 12 hours. 'Day' length = 24 hours
181.                      -1 = sun is below the specified 'horizon' 24 hours
182.                           'Day' length = 0 hours, *trise and *tset are
183.                            both set to the time when the sun is at south.
184.        """
185.         # Compute d of 12h local mean solar time
186.         d = self.daysSince2000Jan0(year,month,day) + 0.5 - (lon/360.0)
187.
188.         # Compute local sidereal time of this moment
189.         sidtime = self.revolution(self.GMST0(d) + 180.0 + lon)
190.
191.         # Compute Sun's RA + Decl at this moment
193.         sRA = res[0]
194.         sdec = res[1]
195.         sr = res[2]
196.
197.         # Compute time when Sun is at south - in hours UT
198.         tsouth = 12.0 - self.rev180(sidtime - sRA)/15.0;
199.
200.         # Compute the Sun's apparent radius, degrees
201.         sradius = 0.2666 / sr;
202.
203.         # Do correction to upper limb, if necessary
204.         if upper_limb:
205.             altit = altit - sradius
206.
207.         # Compute the diurnal arc that the Sun traverses to reach
208.         # the specified altitude altit:
209.
210.         cost = (self.sind(altit) - self.sind(lat) * self.sind(sdec))/\
211.                (self.cosd(lat) * self.cosd(sdec))
212.
213.         if cost >= 1.0:
214.             rc = -1
215.             t = 0.0           # Sun always below altit
216.
217.         elif cost <= -1.0:
218.             rc = +1
219.             t = 12.0;         # Sun always above altit
220.
221.         else:
222.             t = self.acosd(cost)/15.0   # The diurnal arc, hours
223.
224.
225.         # Store rise and set times - in hours UT
226.         return (tsouth-t, tsouth+t)
227.
228.
229.     def __daylen__(self, year, month, day, lon, lat, altit, upper_limb):
230.         """
231.        Note: year,month,date = calendar date, 1801-2099 only.
232.              Eastern longitude positive, Western longitude negative
233.              Northern latitude positive, Southern latitude negative
234.              The longitude value is not critical. Set it to the correct
235.              longitude if you're picky, otherwise set to, say, 0.0
236.              The latitude however IS critical - be sure to get it correct
237.              altit = the altitude which the Sun should cross
238.                      Set to -35/60 degrees for rise/set, -6 degrees
239.                      for civil, -12 degrees for nautical and -18
240.                      degrees for astronomical twilight.
241.                upper_limb: non-zero -> upper limb, zero -> center
242.                      Set to non-zero (e.g. 1) when computing day length
243.                      and to zero when computing day+twilight length.
244.
245.        """
246.
247.         # Compute d of 12h local mean solar time
248.         d = self.daysSince2000Jan0(year,month,day) + 0.5 - (lon/360.0)
249.
250.         # Compute obliquity of ecliptic (inclination of Earth's axis)
251.         obl_ecl = 23.4393 - 3.563E-7 * d
252.
253.         # Compute Sun's position
254.         res = self.sunpos(d)
255.         slon = res[0]
256.         sr = res[1]
257.
258.         # Compute sine and cosine of Sun's declination
259.         sin_sdecl = self.sind(obl_ecl) * self.sind(slon)
260.         cos_sdecl = math.sqrt(1.0 - sin_sdecl * sin_sdecl)
261.
262.         # Compute the Sun's apparent radius, degrees
263.         sradius = 0.2666 / sr
264.
265.         # Do correction to upper limb, if necessary
266.         if upper_limb:
267.             altit = altit - sradius
268.
269.
270.         cost = (self.sind(altit) - self.sind(lat) * sin_sdecl) / \
271.                (self.cosd(lat) * cos_sdecl)
272.         if cost >= 1.0:
273.             t = 0.0             # Sun always below altit
274.
275.         elif cost <= -1.0:
276.             t = 24.0      # Sun always above altit
277.
278.         else:
279.             t = (2.0/15.0) * self.acosd(cost);     # The diurnal arc, hours
280.
281.         return t
282.
283.
284.     def sunpos(self, d):
285.         """
286.        Computes the Sun's ecliptic longitude and distance
287.        at an instant given in d, number of days since
288.        2000 Jan 0.0.  The Sun's ecliptic latitude is not
289.        computed, since it's always very near 0.
290.        """
291.
292.         # Compute mean elements
293.         M = self.revolution(356.0470 + 0.9856002585 * d)
294.         w = 282.9404 + 4.70935E-5 * d
295.         e = 0.016709 - 1.151E-9 * d
296.
297.         # Compute true longitude and radius vector
298.         E = M + e * self.RADEG * self.sind(M) * (1.0 + e * self.cosd(M))
299.         x = self.cosd(E) - e
300.         y = math.sqrt(1.0 - e*e) * self.sind(E)
301.         r = math.sqrt(x*x + y*y)              #Solar distance
302.         v = self.atan2d(y, x)                 # True anomaly
303.         lon = v + w                        # True solar longitude
304.         if lon >= 360.0:
305.             lon = lon - 360.0   # Make it 0..360 degrees
306.
307.         return (lon,r)
308.
309.
311.         """
312.        Returns the angle of the Sun (RA)
313.        the declination (dec) and the distance of the Sun (r)
314.        for a given day d.
315.        """
316.
317.         # Compute Sun's ecliptical coordinates
318.         res = self.sunpos(d)
319.         lon = res[0]  # True solar longitude
320.         r = res[1]    # Solar distance
321.
322.         # Compute ecliptic rectangular coordinates (z=0)
323.         x = r * self.cosd(lon)
324.         y = r * self.sind(lon)
325.
326.         # Compute obliquity of ecliptic (inclination of Earth's axis)
327.         obl_ecl = 23.4393 - 3.563E-7 * d
328.
329.         # Convert to equatorial rectangular coordinates - x is unchanged
330.         z = y * self.sind(obl_ecl)
331.         y = y * self.cosd(obl_ecl)
332.
333.         # Convert to spherical coordinates
334.         RA = self.atan2d(y, x)
335.         dec = self.atan2d(z, math.sqrt(x*x + y*y))
336.
337.         return (RA, dec, r)
338.
339.
340.     def revolution(self, x):
341.         """
342.        This function reduces any angle to within the first revolution
343.        by subtracting or adding even multiples of 360.0 until the
344.        result is >= 0.0 and < 360.0
345.
346.        Reduce angle to within 0..360 degrees
347.        """
348.         return (x - 360.0 * math.floor(x * self.INV360))
349.
350.     def rev180(self, x):
351.         """
352.        Reduce angle to within +180..+180 degrees
353.        """
354.         return (x - 360.0 * math.floor(x * self.INV360 + 0.5))
355.
356.     def GMST0(self, d):
357.         """
358.        This function computes GMST0, the Greenwich Mean Sidereal Time
359.        at 0h UT (i.e. the sidereal time at the Greenwhich meridian at
360.        0h UT).  GMST is then the sidereal time at Greenwich at any
361.        time of the day.  I've generalized GMST0 as well, and define it
362.        as:  GMST0 = GMST - UT  --  this allows GMST0 to be computed at
363.        other times than 0h UT as well.  While this sounds somewhat
365.        GMST like:
366.
367.         GMST = (GMST0) + UT * (366.2422/365.2422)
368.
369.        where (GMST0) is the GMST last time UT was 0 hours, one simply
370.        computes:
371.
372.         GMST = GMST0 + UT
373.
374.        where GMST0 is the GMST "at 0h UT" but at the current moment!
375.        Defined in this way, GMST0 will increase with about 4 min a
376.        day.  It also happens that GMST0 (in degrees, 1 hr = 15 degr)
377.        is equal to the Sun's mean longitude plus/minus 180 degrees!
378.        (if we neglect aberration, which amounts to 20 seconds of arc
379.        or 1.33 seconds of time)
380.        """
381.         # Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr
382.         # L = M + w, as defined in sunpos().  Since I'm too lazy to
383.         # add these numbers, I'll let the C compiler do it for me.
384.         # Any decent C compiler will add the constants at compile
385.         # time, imposing no runtime or code overhead.
386.
387.         sidtim0 = self.revolution((180.0 + 356.0470 + 282.9404) +
388.                                      (0.9856002585 + 4.70935E-5) * d)
389.         return sidtim0;
390.
391.     def solar_altitude(self, latitude, year, month, day):
392.         """
393.        Compute the altitude of the sun. No atmospherical refraction taken
394.        in account.
395.        Altitude of the southern hemisphere are given relative to
396.        true north.
397.        Altitude of the northern hemisphere are given relative to
398.        true south.
399.        Declination is between 23.5° North and 23.5° South depending
400.        on the period of the year.
401.        Source of formula for altitude is PhysicalGeography.net
402.        http://www.physicalgeography.net/fundamentals/6h.html
403.        """
404.         # Compute declination
405.         N = self.daysSince2000Jan0(year, month, day)
407.         declination = res[1]
408.         sr = res[2]
409.
410.         # Compute the altitude
411.         altitude = 90.0 - latitude  + declination
412.
413.         # In the tropical and  in extreme latitude, values over 90 may occurs.
414.         if altitude > 90:
415.             altitude = 90 - (altitude-90)
416.
417.         if altitude < 0:
418.             altitude = 0
419.
420.         return altitude
421.
422.     def get_max_solar_flux(self, latitude, year, month, day):
423.         """
424.        Compute the maximal solar flux to reach the ground for this date and
425.        latitude.
426.        Originaly comes from Environment Canada weather forecast model.
427.        Information was of the public domain before release by Environment Canada
428.        Output is in W/M^2.
429.        """
430.
431.         (fEot, fR0r, tDeclsc) = self.equation_of_time(year, month, day, latitude)
432.         fSF = (tDeclsc[0]+tDeclsc[1])*fR0r
433.
434.         # In the case of a negative declinaison, solar flux is null
435.         if fSF < 0:
436.             fCoeff = 0
437.         else:
438.             fCoeff =  -1.56e-12*fSF**4 + 5.972e-9*fSF**3 -\
439.                      8.364e-6*fSF**2  + 5.183e-3*fSF - 0.435
440.
441.         fSFT = fSF * fCoeff
442.
443.         if fSFT < 0:
444.             fSFT=0
445.
446.         return fSFT
447.
448.     def equation_of_time(self, year, month, day, latitude):
449.         """
450.        Description: Subroutine computing the part of the equation of time
451.                     needed in the computing of the theoritical solar flux
452.                     Correction originating of the CMC GEM model.
453.
454.        Parameters:  int nTime : cTime for the correction of the time.
455.
456.        Returns: tuple (double fEot, double fR0r, tuple tDeclsc)
457.                 dEot: Correction for the equation of time
458.                 dR0r: Corrected solar constant for the equation of time
459.                 tDeclsc: Declinaison
460.        """
461.         # Julian date
462.         nJulianDate = self.Julian(year, month, day)
463.         # Check if it is a leap year
464.         if(calendar.isleap(year)):
465.             fDivide = 366.0
466.         else:
467.             fDivide = 365.0
468.         # Correction for "equation of time"
469.         fA = nJulianDate/fDivide*2*pi
470.         fR0r = self.__Solcons(fA)*0.1367e4
471.         fRdecl = 0.412*math.cos((nJulianDate+10.0)*2.0*pi/fDivide-pi)
472.         fDeclsc1 = self.sind(latitude)*math.sin(fRdecl)
473.         fDeclsc2 = self.cosd(latitude)*math.cos(fRdecl)
474.         tDeclsc = (fDeclsc1, fDeclsc2)
475.         # in minutes
476.         fEot = 0.002733 -7.343*math.sin(fA)+ .5519*math.cos(fA) \
477.                - 9.47*math.sin(2.0*fA) - 3.02*math.cos(2.0*fA) \
478.                - 0.3289*math.sin(3.*fA) -0.07581*math.cos(3.0*fA) \
479.                -0.1935*math.sin(4.0*fA) -0.1245*math.cos(4.0*fA)
480.         # Express in fraction of hour
481.         fEot = fEot/60.0
483.         fEot = fEot*15*pi/180.0
484.
485.         return (fEot, fR0r, tDeclsc)
486.
487.     def __Solcons(self, dAlf):
488.         """
489.        Name: __Solcons
490.
491.        Parameters: [I] double dAlf : Solar constant to correct the excentricity
492.
493.        Returns: double dVar : Variation of the solar constant
494.
495.        Functions Called: cos, sin
496.
497.        Description:  Statement function that calculates the variation of the
498.          solar constant as a function of the julian day. (dAlf, in radians)
499.
500.        Notes: Comes from the
501.
502.        Revision History:
503.        Author          Date            Reason
504.        Miguel Tremblay      June 30th 2004
505.        """
506.
507.         dVar = 1.0/(1.0-9.464e-4*math.sin(dAlf)-0.01671*math.cos(dAlf)- \
508.                     + 1.489e-4*math.cos(2.0*dAlf)-2.917e-5*math.sin(3.0*dAlf)- \
509.                     + 3.438e-4*math.cos(4.0*dAlf))**2
510.         return dVar
511.
512.
513.     def Julian(self, year, month, day):
514.         """
515.        Return julian day.
516.        """
517.         if calendar.isleap(year): # Bissextil year, 366 days
518.             lMonth = [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366]
519.         else: # Normal year, 365 days
520.             lMonth = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365]
521.
522.         nJulian = lMonth[month-1] + day
523.         return nJulian
524.
525.
526.
527. if __name__ == "__main__":
528.
529.     k = Sun()
530.     print k.get_max_solar_flux(46.2, 2004, 01, 30)
531. #    print k.sunRiseSet(2002, 3, 22, 25.42, 62.15)
532.
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