Skip to content
πŸ› οΈToolsShed

Moon Phase Calculator

Calculate the current moon phase, illumination percentage, and lunar cycle information for any date.

About this tool

The Moon Phase Calculator helps you discover the current moon phase, illumination percentage, and detailed lunar cycle information for any dateβ€”past, present, or future. Understanding the moon's appearance and position in its 29.5-day cycle is valuable for astronomy enthusiasts, gardeners following lunar calendars, photographers planning night shoots, and anyone curious about our natural satellite's behavior.

Simply enter any date using the calendar picker, and the tool instantly displays the moon phase name, how much of the lunar disk is illuminated, the number of days into the current cycle, and the next full or new moon date. You can explore the moon's appearance on your birthday, check conditions for upcoming astronomical events, or track how lunar cycles affect activities like planting or fishing.

This calculator uses astronomical algorithms to compute lunar positions with high accuracy, making it reliable for educational projects, creative planning, and casual stargazing. Keep in mind that illumination percentages are approximate snapshots; actual visibility depends on your location, local weather, and time of night.

Frequently Asked Questions

Code Implementation

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']}%")

Comments & Feedback

Comments are powered by Giscus. Sign in with GitHub to leave a comment.