moonphase.py

#!/usr/bin/python3
import datetime
import bisect
import ephem

DAY = 1.0/29.33
MOONPHASE = [
    (0.0/4.0 + DAY, '🌑', 'New moon'),
    (1.0/4.0 - DAY, '🌒', 'Waxing crescent moon'),
    (1.0/4.0 + DAY, '🌓', 'First quarter moon'),
    (2.0/4.0 - DAY, '🌔', 'Waxing gibbous moon'),
    (2.0/4.0 + DAY, '🌕', 'Full moon'),
    (3.0/4.0 - DAY, '🌖', 'Waning gibbous moon'),
    (3.0/4.0 + DAY, '🌗', 'Last quarter moon'),
    (4.0/4.0 - DAY, '🌘', 'Waning crescent moon'),
    (4.0/4.0,       '🌑', 'New moon'),
]
RANGES = [x[0] for x in MOONPHASE]

def get_phase_on_day(ddata):
    """Returns a floating-point number from 0-1. where 0=new, 0.5=full, 1=new"""
    date = ephem.Date(ddata)

    # The following extract the percent time between one new moon and the next
    # This corresponds (somewhat roughly) to the phase of the moon.
    # Note that there is a ephem.Moon().phase(), but this returns the
    # percentage of the moon which is illuminated. This is not really what we
    # want.
    nnm = ephem.next_new_moon    (date)
    pnm = ephem.previous_new_moon(date)
    lunation = (date-pnm)/(nnm-pnm)
    return lunation

lunation = get_phase_on_day(datetime.date.today())
phase = bisect.bisect_right(RANGES, lunation)
print('%.0f%% %s %s' % (lunation * 100.0, MOONPHASE[phase][1], MOONPHASE[phase][2]))