Moon Phase Calculator
Calculate the approximate lunar phase for any date. Uses the Julian Date method and the 29.53059-day synodic period. Accuracy within ~1 day; use an ephemeris for precise astronomical timing.
Moon Phase
Lunar Phase Cycle
| Phase | Cycle Position | Illumination | Rising/Setting |
|---|---|---|---|
| New Moon 🌑 | Day 0–1 | ~0% | Rises at sunrise, sets at sunset |
| Waxing Crescent 🌒 | Day 1–7 | 1–49% | Visible evening western sky |
| First Quarter 🌓 | Day 7–8 | ~50% | Rises at noon, sets at midnight |
| Waxing Gibbous 🌔 | Day 8–14 | 51–99% | Rises afternoon, sets after midnight |
| Full Moon 🌕 | Day 14–15 | ~100% | Rises at sunset, sets at sunrise |
| Waning Gibbous 🌖 | Day 15–22 | 99–51% | Rises after sunset, visible most of night |
| Last Quarter 🌗 | Day 22–23 | ~50% | Rises at midnight, sets at noon |
| Waning Crescent 🌘 | Day 23–29 | 49–1% | Visible pre-dawn eastern sky |
The synodic period (new moon to new moon) is 29 days, 12 hours, 44 minutes, 3 seconds (29.53059 days average).
References & Methodology
- Meeus, J. — Astronomical Algorithms, 2nd ed. (Willmann-Bell, 1998) — Standard reference for Julian Date calculation and lunar phase algorithms; Chapter 49 covers lunation number and phase determination.
- U.S. Naval Observatory (USNO) — Astronomical Almanac — Authoritative annual ephemeris for lunar phases, rise/set times, and eclipse data.
- Brown, E.W. — Tables of the Motion of the Moon (Yale University Press, 1919) — Historical lunar theory basis for synodic period constants used in simplified phase calculations.