Using ephem
's sidereal_time()
method:
import ephem # pip install pyephem (on Python 2)
# pip install ephem (on Python 3)
def solartime(observer, sun=ephem.Sun()):
sun.compute(observer)
# sidereal time == ra (right ascension) is the highest point (noon)
hour_angle = observer.sidereal_time() - sun.ra
return ephem.hours(hour_angle + ephem.hours('12:00')).norm # norm for 24h
Note: ephem.hours
is a float number that represents an angle in radians and converts to/from a string as "hh:mm:ss.ff".
For comparison, here's the "utc + longitude" formula:
import math
from datetime import timedelta
def ul_time(observer):
utc_dt = observer.date.datetime()
longitude = observer.long
return utc_dt + timedelta(hours=longitude / math.pi * 12)
Example
from datetime import datetime
# "solar time" for some other cities
for name in ['Los Angeles', 'New York', 'London',
'Paris', 'Moscow', 'Beijing', 'Tokyo']:
city = ephem.city(name)
print("%-11s %11s %s" % (name, solartime(city),
ul_time(city).strftime('%T')))
# set date, longitude manually
o = ephem.Observer()
o.date = datetime(2012, 4, 15, 1, 0, 2) # some utc time
o.long = '00:00:00.0' # longitude (you could also use a float (radians) here)
print("%s %s" % (solartime(o), ul_time(o).strftime('%T')))
Output
Los Angeles 14:59:34.11 14:44:30
New York 17:56:31.27 17:41:27
London 22:52:02.04 22:36:58
Paris 23:01:56.56 22:46:53
Moscow 1:23:00.33 01:07:57
Beijing 6:38:09.53 06:23:06
Tokyo 8:11:17.81 07:56:15
1:00:00.10 01:00:01
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