Next Full Moon

This countdown targets the next full moon, computed from the real lunar cycle rather than a rounded date. Unlike calendar holidays, a full moon has a precise time: it is the instant when the Moon sits exactly opposite the Sun as seen from Earth. The countdown therefore points at a universal moment, identical in every time zone.

Every 29 and a half days. A lunation — from one full moon to the next — averages 29 days, 12 hours and 44 minutes. It is not constant: the Moon's orbit is elliptical, so the real interval swings by several hours around that average. An approximate date is not good enough.

Why isn't there an eclipse every month? Because the Moon's orbit is tilted about 5° from Earth's. Most of the time the shadow passes above or below. Alignments close enough for an eclipse happen only two or three times a year.

Supermoon, blue moon. A supermoon is a full moon coinciding with perigee, the closest point of the orbit: the disc looks about 7 % wider than average. A blue moon is not blue at all — it is simply the second full moon within one calendar month, which happens every two or three years.

The Moon illusion. A full moon near the horizon looks enormous, yet photographs show it is the same size as when it is high overhead. The effect is in the brain, not in the sky.