Full moon

In the sky

The Moon is now on the far side of Earth from the Sun, so sunlight falls squarely on the side facing us. The exact full moon is an instant, when the two are 180 degrees apart in longitude, but to the eye the Moon looks full for a night or so either side.

A lunar eclipse can only happen at full moon, when Earth's shadow falls across the Moon and can turn it a coppery red. And a full moon low on the horizon looks bigger than one high overhead. That's the moon illusion, a trick of perception: its size in the sky barely changes.

The Moon usually rises about 50 minutes later each night, but around the autumn equinox the gap shrinks to as little as 20 to 30 minutes at mid-northern latitudes. That's why the Harvest Moon seems to rise near sunset several evenings in a row.

In tradition

Almost every culture names its full moons. North American almanacs use names such as the Wolf Moon in January, the Harvest Moon nearest the autumn equinox and the Hunter's Moon after it. Festivals gather around the full moon too, from the Mid-Autumn Festival in East Asia to the monthly Purnima days of the Hindu calendar.

Astrologers read the full moon as a point of culmination: what began at the new moon comes into view, and feelings can sit closer to the surface. It's often treated as a time to notice what's complete and what you're ready to release.