How long is a lunar cycle?

The synodic month—the time from one New Moon to the next—averages about 29.53 days.

What causes lunar phases?

Phases result from the changing geometry of the Sun–Earth–Moon system, which alters how much of the Moon’s sunlit side we see.

Why does the Moon look different in each hemisphere?

Viewers in the Southern Hemisphere see the lunar disk rotated relative to Northern Hemisphere viewers, so the waxing/waning orientation appears flipped.

Informally, a Full Moon near perigee (closest approach to Earth), appearing slightly larger and brighter than average.

Can I see the Moon during the day?

Yes. The Moon is above the horizon in daylight during many phases; check the rise/set times for your location.

Lunar Phase Calculator

Calculate lunar phases and visibility for specific geographic locations.

Today's Moon

9/29/2025 - Check any date below

Select Date

Select date to calculate moon phase

Methodology

This calculator uses the standard astronomical synodic month of 29.53058770576 days with January 6, 2000 (12:24 PM) as the reference new moon. Moon phases are determined based on the lunar day position within the cycle, following the same methodology used by professional astronomical software.

Important Disclaimers:

This calculator provides accuracy suitable for amateur astronomy and general purposes
Results are based on standard astronomical algorithms and reference dates
For professional astronomical research, more precise ephemeris data may be required
Moon phase times are approximate and may vary slightly from other sources
Local viewing conditions and atmospheric effects are not considered

About This Calculator

1. How accurate is this moon phase calculator?

This calculator uses the standard astronomical synodic month of 29.53058770576 days and is accurate for most practical purposes. The calculations are based on the same methods used by professional astronomical software, with accuracy suitable for amateur astronomy, photography, and general interest.

2. What is the difference between lunar day and calendar day?

A lunar day in this context refers to the number of days elapsed since the last new moon in the current lunar cycle. It ranges from 0 to about 29.5 days. This is different from a calendar day, which is a 24-hour period in our standard timekeeping system.

3. Why do moon phases repeat every 29.53 days?

This period, called a synodic month, is the time it takes for the Moon to return to the same phase as seen from Earth. It's longer than the Moon's orbital period (27.3 days) because Earth is also moving in its orbit around the Sun, so the Moon needs extra time to 'catch up' to the same Sun-Earth-Moon alignment.

4. Can I use this calculator for historical dates?

Yes, this calculator works for dates both in the past and future, though accuracy may decrease for dates very far from the reference point (January 6, 2000). For historical astronomical research, more sophisticated calculations accounting for long-term orbital variations might be needed.