Comments on: Phases Of The Moon

By: Mike

Mike — Mon, 12 Apr 2010 20:51:43 +0000

[sourcecode lang="python"] import datetime from math import fmod def moonphase( date=None ): '''return phase of the moon on a given date. date is a datetime.date object. Defaults to today. ''' if date is None: date = datetime.date.today() known_new_moon = datetime.date(2000,1,6) lunar_cycle = 29.530588853 # days per lunation phase_length = lunar_cycle/8 # days per phase days = (date - known_new_moon).days days = fmod(days + phase_length/2, lunar_cycle) phase = int( days * ( 8 / lunar_cycle ) ) phasetext = ("new", "waxing crescent", "first quarter", "waxing gibbous", "full", "waning gibbous", "last quater", "waning crescent") return phase, phasetext[ phase ] [/sourcecode]

By: Maurits

Maurits — Wed, 03 Feb 2010 22:21:32 +0000

A quibble – the phases of the moon are only four:

1) waxing crescent
2) waxing gibbous
3) waning gibbous
4) waning crescent

The other four states (new, first quarter, full, third quarter) are more in the nature of events than phases… that is to say, the moon is only new for an instant.

By: Mark VandeWettering

Mark VandeWettering — Mon, 25 Jan 2010 18:22:55 +0000

Sorry, hit the wrong button.

… was January 6, 18:14 UTC.

By: Mark VandeWettering

Mark VandeWettering — Mon, 25 Jan 2010 18:21:44 +0000

I didn’t have any time for actually coding this up, but John Conway has a way of computing the phase of the moon that can be done in your head as part of his (formerly two vollume, now republished by AK Peterson as 4 volume) series Winning Ways. The “nice” feature of this is that it doesn’t actually require any conversion to julian dates. I think that most of these proposed solutions are slightly off: some don’t perform proper rounding, and most seem to ignore the fact that the first new moon of January 2000 was January 6,

By: iyo

iyo — Sat, 23 Jan 2010 15:09:02 +0000

There's my python version. I'm surprised python's math.fmod(num, n) doesn't give results into <0;n) but it is simple remainder - results are from interval (-n;n). Inverse indexing of list is also possible. Listing of the code:


from datetime import date
from math import fmod


def phaseOfMoon(day):
	period = 29.530588853
	referenceDate = date(2000, 1, 6)
	phases = ["new", "waxing crescent", "first quarter", "waxing gibbous",
		"full", "waning gibbous", "last quarter", "waning crescent"]

	daysDelta = (day - referenceDate).days
	moonAge = fmod(daysDelta, period)

	phaseNum = int( moonAge / (period / len(phases)) )

	return phases[phaseNum]

if __name__ == "__main__":
	samples = [date(2000, 1, 1), date(2000, 1, 6), date(2000, 2, 8), date.today()]
	for sample in samples:
		print sample, "=", phaseOfMoon(sample)

By: novatech

novatech — Fri, 22 Jan 2010 23:48:04 +0000

ruby version [sourcecode lang="ruby"] def julian (year, month, day) a = (14-month)/12 y = year+4800-a m = (12*a)-3+month return day + (153*m+2)/5 + (365*y) + y/4 - y/100 + y/400 - 32045 end def phase (year,month,day) p=(julian(year,month,day)-julian(2000,1,6))%29.530588853 if p<1.84566: return "New" elsif p<5.53699: return "Waxing crescent" elsif p<9.22831: return "First quarter" elsif p<12.91963: return "Waxing gibbous" elsif p<16.61096: return "Full" elsif p<20.30228: return "Waning gibbous" elsif p<23.99361: return "Last quarter" elsif p<27.68493: return "Waning crescent" else return "New" end end print "#{phase(2020,1,23)}\n" print "#{phase(1999,1,6)}\n" print "#{phase(2010,2,10)}\n" print "#{phase(1987,5,10)}\n" [/sourcecode]

By: Remco Niemeijer

Remco Niemeijer — Fri, 22 Jan 2010 09:44:08 +0000

My Haskell solution (see http://bonsaicode.wordpress.com/2010/01/22/programming-praxis-phases-of-the-moon/ for a version with comments):

import Data.Time
import Data.Time.Calendar.Julian
import Data.Fixed

moonPhase :: Integer -> Int -> Int -> String
moonPhase y m d = phase . flip mod' 29.530588853 . fromIntegral $
    diffDays (fromJulian y m d) (fromJulian 2000 1 6) where
    phase x | x <  1.84566 = "New"
            | x <  5.53699 = "Waxing crescent"
            | x <  9.22831 = "First quarter"
            | x < 12.91963 = "Waxing gibbous"
            | x < 16.61096 = "Full"
            | x < 20.30228 = "Waning gibbous"
            | x < 23.99361 = "Last quarter"
            | x < 27.68493 = "Waning crescent"
            | otherwise    = "New"