didier/functions/sunrise.py

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from math import cos, sin, acos, asin, tan
from math import degrees as deg, radians as rad
from datetime import date, datetime, time
import pytz
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()
print('sunrise at ',s.sunrise(when=datetime.datetime.now())
"""
def __init__(self):
self.lat = 51.027169
self.long = 3.710359
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=pytz.timezone("Europe/Brussels"))
self.__preptime(when)
self.__calc()
return Sun.__timefromdecimalday(self.sunrise_t)
def sunset(self, when=None):
if when is None: when = datetime.now(tz=pytz.timezone("Europe/Brussels"))
self.__preptime(when)
self.__calc()
return Sun.__timefromdecimalday(self.sunset_t)
def solarnoon(self, when=None):
if when is None: when = datetime.now(tz=pytz.timezone("Europe/Brussels"))
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