sun.py

from math import cos,sin,acos,asin,tan
from math import degrees as deg, radians as rad
from datetime import date,datetime,time

# this module is not provided here. See text.
from timezone import LocalTimezone

class sun:
 """ 
 Calculate sunrise and sunset based on equations from NOAA
 http://www.srrb.noaa.gov/highlights/sunrise/calcdetails.html

 typical use, calculating the sunrise at the present day:
 
 import datetime
 import sunrise
 s = sun(lat=49,long=3)
 print('sunrise at ',s.sunrise(when=datetime.datetime.now())
 """
 def __init__(self,lat=52.37,long=4.90): # default Amsterdam
  self.lat=lat
  self.long=long
  
 def sunrise(self,when=None):
  """
  return the time of sunrise as a datetime.time object
  when is a datetime.datetime object. If none is given
  a local time zone is assumed (including daylight saving
  if present)
  """
  if when is None : when = datetime.now(tz=LocalTimezone())
  self.__preptime(when)
  self.__calc()
  return sun.__timefromdecimalday(self.sunrise_t)
  
 def sunset(self,when=None):
  if when is None : when = datetime.now(tz=LocalTimezone())
  self.__preptime(when)
  self.__calc()
  return sun.__timefromdecimalday(self.sunset_t)
  
 def solarnoon(self,when=None):
  if when is None : when = datetime.now(tz=LocalTimezone())
  self.__preptime(when)
  self.__calc()
  return sun.__timefromdecimalday(self.solarnoon_t)
  
 @staticmethod
 def __timefromdecimalday(day):
  """
  returns a datetime.time object.
  
  day is a decimal day between 0.0 and 1.0, e.g. noon = 0.5
  """
  hours  = 24.0*day
  h      = int(hours)
  minutes= (hours-h)*60
  m      = int(minutes)
  seconds= (minutes-m)*60
  s      = int(seconds)
  return time(hour=h,minute=m,second=s)

 def __preptime(self,when):
  """
  Extract information in a suitable format from when, 
  a datetime.datetime object.
  """
  # datetime days are numbered in the Gregorian calendar
  # while the calculations from NOAA are distibuted as
  # OpenOffice spreadsheets with days numbered from
  # 1/1/1900. The difference are those numbers taken for 
  # 18/12/2010
  self.day = when.toordinal()-(734124-40529)
  t=when.time()
  self.time= (t.hour + t.minute/60.0 + t.second/3600.0)/24.0
  
  self.timezone=0
  offset=when.utcoffset()
  if not offset is None:
   self.timezone=offset.seconds/3600.0
  
 def __calc(self):
  """
  Perform the actual calculations for sunrise, sunset and
  a number of related quantities.
  
  The results are stored in the instance variables
  sunrise_t, sunset_t and solarnoon_t
  """
  timezone = self.timezone # in hours, east is positive
  longitude= self.long     # in decimal degrees, east is positive
  latitude = self.lat      # in decimal degrees, north is positive

  time  = self.time # percentage past midnight, i.e. noon  is 0.5
  day      = self.day     # daynumber 1=1/1/1900
 
  Jday     =day+2415018.5+time-timezone/24 # Julian day
  Jcent    =(Jday-2451545)/36525    # Julian century

  Manom    = 357.52911+Jcent*(35999.05029-0.0001537*Jcent)
  Mlong    = 280.46646+Jcent*(36000.76983+Jcent*0.0003032)%360
  Eccent   = 0.016708634-Jcent*(0.000042037+0.0001537*Jcent)
  Mobliq   = 23+(26+((21.448-Jcent*(46.815+Jcent*(0.00059-Jcent*0.001813))))/60)/60
  obliq    = Mobliq+0.00256*cos(rad(125.04-1934.136*Jcent))
  vary     = tan(rad(obliq/2))*tan(rad(obliq/2))
  Seqcent  = sin(rad(Manom))*(1.914602-Jcent*(0.004817+0.000014*Jcent))+sin(rad(2*Manom))*(0.019993-0.000101*Jcent)+sin(rad(3*Manom))*0.000289
  Struelong= Mlong+Seqcent
  Sapplong = Struelong-0.00569-0.00478*sin(rad(125.04-1934.136*Jcent))
  declination = deg(asin(sin(rad(obliq))*sin(rad(Sapplong))))
  
  eqtime   = 4*deg(vary*sin(2*rad(Mlong))-2*Eccent*sin(rad(Manom))+4*Eccent*vary*sin(rad(Manom))*cos(2*rad(Mlong))-0.5*vary*vary*sin(4*rad(Mlong))-1.25*Eccent*Eccent*sin(2*rad(Manom)))

  hourangle= deg(acos(cos(rad(90.833))/(cos(rad(latitude))*cos(rad(declination)))-tan(rad(latitude))*tan(rad(declination))))

  self.solarnoon_t=(720-4*longitude-eqtime+timezone*60)/1440
  self.sunrise_t  =self.solarnoon_t-hourangle*4/1440
  self.sunset_t   =self.solarnoon_t+hourangle*4/1440

if __name__ == "__main__":
 s=sun(lat=52.37,long=4.90)
 print(datetime.today())
 print(s.sunrise(),s.solarnoon(),s.sunset())