A supermoon is a full moon or a new moon that approximately coincides with the closest distance that the Moon reaches to Earth in its elliptic orbit, resulting in a larger-than-usual apparent size of the lunar disk as seen from Earth. The technical name is the perigee syzygy of the Earth–Moon–Sun system. The term supermoon is not astronomical, but originated in modern astrology. The association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events like earthquakes and volcanic eruptions, but there is no such link.

The opposite phenomenon, an apogee syzygy, has been called a micromoon, though this term is not as widespread as supermoon.

The most recent supermoon occurrence was on December 3, 2017, and the next one will be on January 2, 2018. The one on November 14, 2016 was the closest supermoon since January 26, 1948, and will not be surpassed until November 25, 2034. The closest supermoon of the century will occur on December 6, 2052.