Calculate Lunar Phase

moonphase.py

#!/usr/bin/env python
"""
moonphase.py - Calculate Lunar Phase
Author: Sean B. Palmer, inamidst.com
Cf. http://en.wikipedia.org/wiki/Lunar_phase#Lunar_phase_calculation
"""

import math, decimal, datetime
dec = decimal.Decimal

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

   diff = now - datetime.datetime(2001, 1, 1)
   days = dec(diff.days) + (dec(diff.seconds) / dec(86400))
   lunations = dec("0.20439731") + (days * dec("0.03386319269"))

   return lunations % dec(1)

def phase(pos): 
   index = (pos * dec(8)) + dec("0.5")
   index = math.floor(index)
   return {
      0: "New Moon", 
      1: "Waxing Crescent", 
      2: "First Quarter", 
      3: "Waxing Gibbous", 
      4: "Full Moon", 
      5: "Waning Gibbous", 
      6: "Last Quarter", 
      7: "Waning Crescent"
   }[int(index) & 7]

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

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

if __name__=="__main__": 
   main()

@sbp howdy! I did leave credit in the script and I honestly don't remember where I came across it or why I originally shared it. I posted this gist 9 years ago! Thanks for pointing folks to the original source and offering support.