What Is a Supermoon?

The Moon orbit around Earth is elliptical, with a perigee (closest point) of about 356,500 km and an apogee (farthest) of about 406,700 km. When a full moon occurs within about 90% of perigee, it is popularly called a supermoon. The Moon appears up to 14% larger and 30% brighter than a full moon at apogee (sometimes called a micromoon). The term was coined by astrologer Richard Nolle in 1979 and has no official astronomical definition, though NASA and other agencies now use it widely. Supermoons occur 3–4 times per year. The size difference is subtle to the naked eye but measurable in photographs.