get todays lunation and moon dates for the year, any year

moon.py

#!/usr/bin/env python3
'''
Using PyEphem for some scientific fun http://rhodesmill.org/pyephem/

This script shows lunation and moon dates for the year. Maybe more
in a future.

make alias for your shell
alias moon="python3 /path/to/moon.py"
'''
import datetime
import ephem
from tabulate import tabulate
import argparse


def get_phase_on_day(year, month, day):
    '''
    Returns a floating-point number from 0-1. where 0=new, 0.5=full, 1=new"""
    Ephem stores its date numbers as floating points, which the following uses
    to conveniently extract the percent time between one new moon and the next
    This corresponds (somewhat roughly) to the phase of the moon.

    Use Year, Month, Day as arguments
    '''
    date = ephem.Date(datetime.date(year, month, day))

    nnm = ephem.next_new_moon(date)
    pnm = ephem.previous_new_moon(date)

    lunation = (date - pnm) / (nnm - pnm)

    '''
    Note that there is a ephem.Moon().phase() command, but this returns the
    percentage of the moon which is illuminated. This is not really what we want.
    '''
    return 29.530588853 * lunation


def get_moons_in_year(year):
    '''
    Returns a list of the full and new moons in a year. The list contains tuples
    of either the form (DATE,'full') or the form (DATE,'new')
    '''
    moons = []

    date = ephem.Date(datetime.date(year, 1, 1))
    while date.datetime().year == year:
        date = ephem.next_full_moon(date)
        date1 = ephem.localtime(date)
        date = ephem.next_new_moon(date)
        date2 = ephem.localtime(date)
        moons.append(['{0:%a, %d %b %H:%M}'.format(date1),
            '{0:%a, %d %b %H:%M}'.format(date2)])

    '''
    Note that previous_first_quarter_moon() and previous_last_quarter_moon()
    are also methods
    '''
    # moons.sort(key=lambda x: x[0])

    return moons


def getArgs(argv=None):
    '''
    Command line arguments...
    '''
    parser = argparse.ArgumentParser(description='Play with astral bodies.',
                        formatter_class=argparse.ArgumentDefaultsHelpFormatter)
    parser.add_argument('-y', '--year',
                        default='2017',
                        help='Prints moon phase dates in a given year')
    return parser.parse_args(argv)


if __name__ == '__main__':

    args = getArgs()
    year = int(args.year)
    today = datetime.datetime.now()
    year, month, day = today.year, today.month, today.day
    date = ephem.Date(datetime.date(year, month, day))
    print("Today's lunation: ", '{:02.1f}'.format(get_phase_on_day(year, month, day)))
    # print(get_phase_on_day(2017, 5, 11))

    mp = get_moons_in_year(year)
    headers = ['Full Moon', 'New Moon']
    print(tabulate(mp, headers, tablefmt="simple"))