Phase of the moon

moonphase.py

#!/usr/bin/env python
# http://en.wikipedia.org/wiki/Lunar_phase#Calculating_phase

import math, decimal, datetime
dec = decimal.Decimal

def position(now=None): 
   if now is None: 
      now = datetime.datetime.now()

   diff = now - datetime.datetime(2011, 11, 25, 6, 9, 35)
   days = dec(diff.days) + (dec(diff.seconds) / dec(86400))
   lunations = days % dec("29.530588853")

   return lunations

def phase(pos): 
   sixteenth = dec("29.530588853") / dec(16)
   if pos < sixteenth: 
      return "New Moon"
   elif pos < sixteenth * 3: 
      return "Waxing Crescent"
   elif pos < sixteenth * 5: 
      return "First Quarter"
   elif pos < sixteenth * 7: 
      return "Waxing Gibbous"
   elif pos < sixteenth * 9: 
      return "Full Moon"
   elif pos < sixteenth * 11: 
      return "Waning Gibbous"
   elif pos < sixteenth * 13: 
      return "Last Quarter"
   elif pos < sixteenth * 15: 
      return "Waning Crescent"
   else: return "New Moon"

def main(): 
   pos = position()
   phasename = phase(pos)

   roundedpos = round(float(pos / dec("29.530588853")), 3)
   print "%s (%s)" % (phasename, roundedpos)

if __name__=="__main__": 
   main()