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60 lines
1.8 KiB
Python
60 lines
1.8 KiB
Python
"""
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https://en.wikipedia.org/wiki/Computus#Gauss'_Easter_algorithm
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"""
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import math
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from datetime import datetime, timedelta
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def gauss_easter(year: int) -> datetime:
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"""
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Calculation Gregorian easter date for given year
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>>> gauss_easter(2007)
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datetime.datetime(2007, 4, 8, 0, 0)
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>>> gauss_easter(2008)
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datetime.datetime(2008, 3, 23, 0, 0)
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>>> gauss_easter(2020)
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datetime.datetime(2020, 4, 12, 0, 0)
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>>> gauss_easter(2021)
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datetime.datetime(2021, 4, 4, 0, 0)
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"""
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metonic_cycle = year % 19
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julian_leap_year = year % 4
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non_leap_year = year % 7
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leap_day_inhibits = math.floor(year / 100)
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lunar_orbit_correction = math.floor((13 + 8 * leap_day_inhibits) / 25)
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leap_day_reinstall_number = leap_day_inhibits / 4
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secular_moon_shift = (
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15 - lunar_orbit_correction + leap_day_inhibits - leap_day_reinstall_number
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) % 30
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century_starting_point = (4 + leap_day_inhibits - leap_day_reinstall_number) % 7
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# days to be added to March 21
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days_to_add = (19 * metonic_cycle + secular_moon_shift) % 30
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# PHM -> Paschal Full Moon
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days_from_phm_to_sunday = (
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2 * julian_leap_year
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+ 4 * non_leap_year
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+ 6 * days_to_add
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+ century_starting_point
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) % 7
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if days_to_add == 29 and days_from_phm_to_sunday == 6:
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return datetime(year, 4, 19)
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elif days_to_add == 28 and days_from_phm_to_sunday == 6:
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return datetime(year, 4, 18)
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else:
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return datetime(year, 3, 22) + timedelta(
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days=int(days_to_add + days_from_phm_to_sunday)
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)
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if __name__ == "__main__":
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for year in (1994, 2000, 2010, 2021, 2023):
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tense = "will be" if year > datetime.now().year else "was"
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print(f"Easter in {year} {tense} {gauss_easter(year)}")
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