Moon phases: how they work and when the full moons are

The Moon doesn’t make its own light; we see the half of it that faces the Sun. As the Moon orbits Earth, the angle between Sun, Earth and Moon changes, and so does how much of the sunlit half we can see. That changing view is what we call the phases of the Moon.

The four principal phases

• New moon — the Moon is roughly between Earth and Sun, and its lit side faces away from us.
• First quarter — about a week later, the right half is lit (seen from the Northern Hemisphere).
• Full moon — Earth is roughly between Sun and Moon, and the whole face is lit.
• Last quarter — the left half is lit, and the Moon rises around midnight.

Between them are the crescent and gibbous phases. A full cycle, from new moon to new moon, is called a synodic month and lasts about 29.53 days, so the principal phases come roughly every 7.4 days.

Full moons in 2027

There is no “blue moon” (a second full moon in one calendar month) in 2027. The traditional names come from North American and European folklore; the Harvest Moon is the full moon closest to the September equinox, so it sometimes falls in October.

How accurate are calendar moon phases?

The exact moment of a phase is a single instant, so the calendar date depends on your time zone. Our calendars calculate phases from the average lunar cycle, which is accurate to within about a day; for astronomy, photography or tide planning, check an observatory or almanac for the exact time.

Moon phases on printable calendars

Every monthly calendar here shows the four principal phases as small icons beside the date and in the header. Try the current monthly calendar or browse 2027 monthly calendars; you can hide the icons with the “Moon phases” switch.