Moon Phase Calculator
Pick any date and find out what the moon looks like. This calculator tells you the exact phase, how much of the moon is illuminated, and when the next full moon and new moon will happen. Great for photographers, gardeners, and anyone who just loves looking up.
The moon goes through a complete cycle every 29.53 days (called the synodic month). The eight phases are:
- New Moon -- 0% illuminated, invisible
- Waxing Crescent -- 1-49% illuminated, growing
- First Quarter -- 50% illuminated (right half)
- Waxing Gibbous -- 51-99% illuminated, still growing
- Full Moon -- 100% illuminated
- Waning Gibbous -- 99-51% illuminated, shrinking
- Last Quarter -- 50% illuminated (left half)
- Waning Crescent -- 49-1% illuminated, almost gone
How the Calculation Works
We use a known new moon date (January 6, 2000) as our reference point. By calculating the number of days between that reference and your chosen date, then dividing by the synodic month (29.530588853 days), the remainder tells us where we are in the current lunar cycle.
This method is accurate to within a few hours for dates in the 1900-2100 range. For precise astronomical calculations, factors like lunar orbit eccentricity and solar perturbations would need to be included.