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sun.py
#!/usr/bin/env python
# -*- coding: iso-8859-1 -*-
"""
SUNRISET.C - computes Sun rise/set times, start/end of twilight, and
the length of the day at any date and latitude
Written as DAYLEN.C, 1989-08-16
Modified to SUNRISET.C, 1992-12-01
(c) Paul Schlyter, 1989, 1992
Released to the public domain by Paul Schlyter, December 1992
Direct conversion to Java
Sean Russell <ser@germane-software.com>
Conversion to Python Class, 2002-03-21
Henrik Härkönen <radix@kortis.to>
Solar Altitude added by Miguel Tremblay 2005-01-16
Solar flux, equation of time and import of python library
added by Miguel Tremblay 2007-11-22
2007-12-12 - v1.5 by Miguel Tremblay: bug fix to solar flux calculation
found via: http://kortis.to/radix/python/code/Sun.py
"""
SUN_PY_VERSION = 1.5
import math
from math import pi
import calendar
class Sun:
def __init__(self):
""""""
# Some conversion factors between radians and degrees
self.RADEG = 180.0 / pi
self.DEGRAD = pi / 180.0
self.INV360 = 1.0 / 360.0
def daysSince2000Jan0(self, y, m, d):
"""A macro to compute the number of days elapsed since 2000 Jan 0.0
(which is equal to 1999 Dec 31, 0h UT)"""
return (367*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530)
# The trigonometric functions in degrees
def sind(self, x):
"""Returns the sin in degrees"""
return math.sin(x * self.DEGRAD)
def cosd(self, x):
"""Returns the cos in degrees"""
return math.cos(x * self.DEGRAD)
def tand(self, x):
"""Returns the tan in degrees"""
return math.tan(x * self.DEGRAD)
def atand(self, x):
"""Returns the arc tan in degrees"""
return math.atan(x) * self.RADEG
def asind(self, x):
"""Returns the arc sin in degrees"""
return math.asin(x) * self.RADEG
def acosd(self, x):
"""Returns the arc cos in degrees"""
return math.acos(x) * self.RADEG
def atan2d(self, y, x):
"""Returns the atan2 in degrees"""
return math.atan2(y, x) * self.RADEG
# Following are some macros around the "workhorse" function __daylen__
# They mainly fill in the desired values for the reference altitude
# below the horizon, and also selects whether this altitude should
# refer to the Sun's center or its upper limb.
def dayLength(self, year, month, day, lon, lat):
"""
This macro computes the length of the day, from sunrise to sunset.
Sunrise/set is considered to occur when the Sun's upper limb is
35 arc minutes below the horizon (this accounts for the refraction
of the Earth's atmosphere).
"""
return self.__daylen__(year, month, day, lon, lat, -35.0/60.0, 1)
def dayCivilTwilightLength(self, year, month, day, lon, lat):
"""
This macro computes the length of the day, including civil twilight.
Civil twilight starts/ends when the Sun's center is 6 degrees below
the horizon.
"""
return self.__daylen__(year, month, day, lon, lat, -6.0, 0)
def dayNauticalTwilightLength(self, year, month, day, lon, lat):
"""
This macro computes the length of the day, incl. nautical twilight.
Nautical twilight starts/ends when the Sun's center is 12 degrees
below the horizon.
"""
return self.__daylen__(year, month, day, lon, lat, -12.0, 0)
def dayAstronomicalTwilightLength(self, year, month, day, lon, lat):
"""
This macro computes the length of the day, incl. astronomical twilight.
Astronomical twilight starts/ends when the Sun's center is 18 degrees
below the horizon.
"""
return self.__daylen__(year, month, day, lon, lat, -18.0, 0)
def sunRiseSet(self, year, month, day, lon, lat):
"""
This macro computes times for sunrise/sunset.
Sunrise/set is considered to occur when the Sun's upper limb is
35 arc minutes below the horizon (this accounts for the refraction
of the Earth's atmosphere).
"""
return self.__sunriset__(year, month, day, lon, lat, -35.0/60.0, 1)
def civilTwilight(self, year, month, day, lon, lat):
"""
This macro computes the start and end times of civil twilight.
Civil twilight starts/ends when the Sun's center is 6 degrees below
the horizon.
"""
return self.__sunriset__(year, month, day, lon, lat, -6.0, 0)
def nauticalTwilight(self, year, month, day, lon, lat):
"""
This macro computes the start and end times of nautical twilight.
Nautical twilight starts/ends when the Sun's center is 12 degrees
below the horizon.
"""
return self.__sunriset__(year, month, day, lon, lat, -12.0, 0)
def astronomicalTwilight(self, year, month, day, lon, lat):
"""
This macro computes the start and end times of astronomical twilight.
Astronomical twilight starts/ends when the Sun's center is 18 degrees
below the horizon.
"""
return self.__sunriset__(year, month, day, lon, lat, -18.0, 0)
# The "workhorse" function for sun rise/set times
def __sunriset__(self, year, month, day, lon, lat, altit, upper_limb):
"""
Note: year,month,date = calendar date, 1801-2099 only.
Eastern longitude positive, Western longitude negative
Northern latitude positive, Southern latitude negative
The longitude value IS critical in this function!
altit = the altitude which the Sun should cross
Set to -35/60 degrees for rise/set, -6 degrees
for civil, -12 degrees for nautical and -18
degrees for astronomical twilight.
upper_limb: non-zero -> upper limb, zero -> center
Set to non-zero (e.g. 1) when computing rise/set
times, and to zero when computing start/end of
twilight.
*rise = where to store the rise time
*set = where to store the set time
Both times are relative to the specified altitude,
and thus this function can be used to compute
various twilight times, as well as rise/set times
Return value: 0 = sun rises/sets this day, times stored at
*trise and *tset.
+1 = sun above the specified 'horizon' 24 hours.
*trise set to time when the sun is at south,
minus 12 hours while *tset is set to the south
time plus 12 hours. 'Day' length = 24 hours
-1 = sun is below the specified 'horizon' 24 hours
'Day' length = 0 hours, *trise and *tset are
both set to the time when the sun is at south.
"""
# Compute d of 12h local mean solar time
d = self.daysSince2000Jan0(year,month,day) + 0.5 - (lon/360.0)
# Compute local sidereal time of this moment
sidtime = self.revolution(self.GMST0(d) + 180.0 + lon)
# Compute Sun's RA + Decl at this moment
res = self.sunRADec(d)
sRA = res[0]
sdec = res[1]
sr = res[2]
# Compute time when Sun is at south - in hours UT
tsouth = 12.0 - self.rev180(sidtime - sRA)/15.0;
# Compute the Sun's apparent radius, degrees
sradius = 0.2666 / sr;
# Do correction to upper limb, if necessary
if upper_limb:
altit = altit - sradius
# Compute the diurnal arc that the Sun traverses to reach
# the specified altitude altit:
cost = (self.sind(altit) - self.sind(lat) * self.sind(sdec))/\
(self.cosd(lat) * self.cosd(sdec))
if cost >= 1.0:
rc = -1
t = 0.0 # Sun always below altit
elif cost <= -1.0:
rc = +1
t = 12.0; # Sun always above altit
else:
t = self.acosd(cost)/15.0 # The diurnal arc, hours
# Store rise and set times - in hours UT
return (tsouth-t, tsouth+t)
def __daylen__(self, year, month, day, lon, lat, altit, upper_limb):
"""
Note: year,month,date = calendar date, 1801-2099 only.
Eastern longitude positive, Western longitude negative
Northern latitude positive, Southern latitude negative
The longitude value is not critical. Set it to the correct
longitude if you're picky, otherwise set to, say, 0.0
The latitude however IS critical - be sure to get it correct
altit = the altitude which the Sun should cross
Set to -35/60 degrees for rise/set, -6 degrees
for civil, -12 degrees for nautical and -18
degrees for astronomical twilight.
upper_limb: non-zero -> upper limb, zero -> center
Set to non-zero (e.g. 1) when computing day length
and to zero when computing day+twilight length.
"""
# Compute d of 12h local mean solar time
d = self.daysSince2000Jan0(year,month,day) + 0.5 - (lon/360.0)
# Compute obliquity of ecliptic (inclination of Earth's axis)
obl_ecl = 23.4393 - 3.563E-7 * d
# Compute Sun's position
res = self.sunpos(d)
slon = res[0]
sr = res[1]
# Compute sine and cosine of Sun's declination
sin_sdecl = self.sind(obl_ecl) * self.sind(slon)
cos_sdecl = math.sqrt(1.0 - sin_sdecl * sin_sdecl)
# Compute the Sun's apparent radius, degrees
sradius = 0.2666 / sr
# Do correction to upper limb, if necessary
if upper_limb:
altit = altit - sradius
cost = (self.sind(altit) - self.sind(lat) * sin_sdecl) / \
(self.cosd(lat) * cos_sdecl)
if cost >= 1.0:
t = 0.0 # Sun always below altit
elif cost <= -1.0:
t = 24.0 # Sun always above altit
else:
t = (2.0/15.0) * self.acosd(cost); # The diurnal arc, hours
return t
def sunpos(self, d):
"""
Computes the Sun's ecliptic longitude and distance
at an instant given in d, number of days since
2000 Jan 0.0. The Sun's ecliptic latitude is not
computed, since it's always very near 0.
"""
# Compute mean elements
M = self.revolution(356.0470 + 0.9856002585 * d)
w = 282.9404 + 4.70935E-5 * d
e = 0.016709 - 1.151E-9 * d
# Compute true longitude and radius vector
E = M + e * self.RADEG * self.sind(M) * (1.0 + e * self.cosd(M))
x = self.cosd(E) - e
y = math.sqrt(1.0 - e*e) * self.sind(E)
r = math.sqrt(x*x + y*y) #Solar distance
v = self.atan2d(y, x) # True anomaly
lon = v + w # True solar longitude
if lon >= 360.0:
lon = lon - 360.0 # Make it 0..360 degrees
return (lon,r)
def sunRADec(self, d):
"""
Returns the angle of the Sun (RA)
the declination (dec) and the distance of the Sun (r)
for a given day d.
"""
# Compute Sun's ecliptical coordinates
res = self.sunpos(d)
lon = res[0] # True solar longitude
r = res[1] # Solar distance
# Compute ecliptic rectangular coordinates (z=0)
x = r * self.cosd(lon)
y = r * self.sind(lon)
# Compute obliquity of ecliptic (inclination of Earth's axis)
obl_ecl = 23.4393 - 3.563E-7 * d
# Convert to equatorial rectangular coordinates - x is unchanged
z = y * self.sind(obl_ecl)
y = y * self.cosd(obl_ecl)
# Convert to spherical coordinates
RA = self.atan2d(y, x)
dec = self.atan2d(z, math.sqrt(x*x + y*y))
return (RA, dec, r)
def revolution(self, x):
"""
This function reduces any angle to within the first revolution
by subtracting or adding even multiples of 360.0 until the
result is >= 0.0 and < 360.0
Reduce angle to within 0..360 degrees
"""
return (x - 360.0 * math.floor(x * self.INV360))
def rev180(self, x):
"""
Reduce angle to within +180..+180 degrees
"""
return (x - 360.0 * math.floor(x * self.INV360 + 0.5))
def GMST0(self, d):
"""
This function computes GMST0, the Greenwich Mean Sidereal Time
at 0h UT (i.e. the sidereal time at the Greenwhich meridian at
0h UT). GMST is then the sidereal time at Greenwich at any
time of the day. I've generalized GMST0 as well, and define it
as: GMST0 = GMST - UT -- this allows GMST0 to be computed at
other times than 0h UT as well. While this sounds somewhat
contradictory, it is very practical: instead of computing
GMST like:
GMST = (GMST0) + UT * (366.2422/365.2422)
where (GMST0) is the GMST last time UT was 0 hours, one simply
computes:
GMST = GMST0 + UT
where GMST0 is the GMST "at 0h UT" but at the current moment!
Defined in this way, GMST0 will increase with about 4 min a
day. It also happens that GMST0 (in degrees, 1 hr = 15 degr)
is equal to the Sun's mean longitude plus/minus 180 degrees!
(if we neglect aberration, which amounts to 20 seconds of arc
or 1.33 seconds of time)
"""
# Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr
# L = M + w, as defined in sunpos(). Since I'm too lazy to
# add these numbers, I'll let the C compiler do it for me.
# Any decent C compiler will add the constants at compile
# time, imposing no runtime or code overhead.
sidtim0 = self.revolution((180.0 + 356.0470 + 282.9404) +
(0.9856002585 + 4.70935E-5) * d)
return sidtim0;
def solar_altitude(self, latitude, year, month, day):
"""
Compute the altitude of the sun. No atmospherical refraction taken
in account.
Altitude of the southern hemisphere are given relative to
true north.
Altitude of the northern hemisphere are given relative to
true south.
Declination is between 23.5° North and 23.5° South depending
on the period of the year.
Source of formula for altitude is PhysicalGeography.net
http://www.physicalgeography.net/fundamentals/6h.html
"""
# Compute declination
N = self.daysSince2000Jan0(year, month, day)
res = self.sunRADec(N)
declination = res[1]
sr = res[2]
# Compute the altitude
altitude = 90.0 - latitude + declination
# In the tropical and in extreme latitude, values over 90 may occurs.
if altitude > 90:
altitude = 90 - (altitude-90)
if altitude < 0:
altitude = 0
return altitude
def get_max_solar_flux(self, latitude, year, month, day):
"""
Compute the maximal solar flux to reach the ground for this date and
latitude.
Originaly comes from Environment Canada weather forecast model.
Information was of the public domain before release by Environment Canada
Output is in W/M^2.
"""
(fEot, fR0r, tDeclsc) = self.equation_of_time(year, month, day, latitude)
fSF = (tDeclsc[0]+tDeclsc[1])*fR0r
# In the case of a negative declinaison, solar flux is null
if fSF < 0:
fCoeff = 0
else:
fCoeff = -1.56e-12*fSF**4 + 5.972e-9*fSF**3 -\
8.364e-6*fSF**2 + 5.183e-3*fSF - 0.435
fSFT = fSF * fCoeff
if fSFT < 0:
fSFT=0
return fSFT
def equation_of_time(self, year, month, day, latitude):
"""
Description: Subroutine computing the part of the equation of time
needed in the computing of the theoritical solar flux
Correction originating of the CMC GEM model.
Parameters: int nTime : cTime for the correction of the time.
Returns: tuple (double fEot, double fR0r, tuple tDeclsc)
dEot: Correction for the equation of time
dR0r: Corrected solar constant for the equation of time
tDeclsc: Declinaison
"""
# Julian date
nJulianDate = self.Julian(year, month, day)
# Check if it is a leap year
if(calendar.isleap(year)):
fDivide = 366.0
else:
fDivide = 365.0
# Correction for "equation of time"
fA = nJulianDate/fDivide*2*pi
fR0r = self.__Solcons(fA)*0.1367e4
fRdecl = 0.412*math.cos((nJulianDate+10.0)*2.0*pi/fDivide-pi)
fDeclsc1 = self.sind(latitude)*math.sin(fRdecl)
fDeclsc2 = self.cosd(latitude)*math.cos(fRdecl)
tDeclsc = (fDeclsc1, fDeclsc2)
# in minutes
fEot = 0.002733 -7.343*math.sin(fA)+ .5519*math.cos(fA) \
- 9.47*math.sin(2.0*fA) - 3.02*math.cos(2.0*fA) \
- 0.3289*math.sin(3.*fA) -0.07581*math.cos(3.0*fA) \
-0.1935*math.sin(4.0*fA) -0.1245*math.cos(4.0*fA)
# Express in fraction of hour
fEot = fEot/60.0
# Express in radians
fEot = fEot*15*pi/180.0
return (fEot, fR0r, tDeclsc)
def __Solcons(self, dAlf):
"""
Name: __Solcons
Parameters: [I] double dAlf : Solar constant to correct the excentricity
Returns: double dVar : Variation of the solar constant
Functions Called: cos, sin
Description: Statement function that calculates the variation of the
solar constant as a function of the julian day. (dAlf, in radians)
Notes: Comes from the
Revision History:
Author Date Reason
Miguel Tremblay June 30th 2004
"""
dVar = 1.0/(1.0-9.464e-4*math.sin(dAlf)-0.01671*math.cos(dAlf)- \
+ 1.489e-4*math.cos(2.0*dAlf)-2.917e-5*math.sin(3.0*dAlf)- \
+ 3.438e-4*math.cos(4.0*dAlf))**2
return dVar
def Julian(self, year, month, day):
"""
Return julian day.
"""
if calendar.isleap(year): # Bissextil year, 366 days
lMonth = [0, 31, 60, 91, 121, 152, 182, 213, 244, 274, 305, 335, 366]
else: # Normal year, 365 days
lMonth = [0, 31, 59, 90, 120, 151, 181, 212, 243, 273, 304, 334, 365]
nJulian = lMonth[month-1] + day
return nJulian
if __name__ == "__main__":
k = Sun()
print k.get_max_solar_flux(46.2, 2004, 01, 30)
# print k.sunRiseSet(2002, 3, 22, 25.42, 62.15)
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