Moon Phase Calculator

import math
from datetime import date, datetime

def calculate_moon_phase(year: int, month: int, day: int) -> dict:
    """
    Calculate moon phase using the Conway algorithm.
    Returns phase name, illumination percentage, and age in days.
    """
    # Julian date calculation
    if month <= 2:
        year -= 1
        month += 12

    A = int(year / 100)
    B = 2 - A + int(A / 4)
    julian = int(365.25 * (year + 4716)) + int(30.6001 * (month + 1)) + day + B - 1524.5

    # Days since known new moon (Jan 6, 2000)
    known_new_moon = 2451549.5
    lunation = 29.53058868

    age = (julian - known_new_moon) % lunation
    illumination = (1 - math.cos(2 * math.pi * age / lunation)) / 2

    # Phase name
    phases = [
        (0.03, "New Moon"), (0.22, "Waxing Crescent"), (0.28, "First Quarter"),
        (0.47, "Waxing Gibbous"), (0.53, "Full Moon"), (0.72, "Waning Gibbous"),
        (0.78, "Last Quarter"), (0.97, "Waning Crescent"), (1.00, "New Moon")
    ]
    fraction = age / lunation
    phase_name = next(name for threshold, name in phases if fraction <= threshold)

    return {
        "age_days": round(age, 2),
        "illumination_pct": round(illumination * 100, 1),
        "phase": phase_name,
        "fraction": round(fraction, 4)
    }

result = calculate_moon_phase(2024, 1, 15)
print(f"Phase: {result['phase']}")
print(f"Age: {result['age_days']} days")
print(f"Illumination: {result['illumination_pct']}%")