A "Supermoon" is the coincidence of a full moon or a new moon with the closest approach the Moon makes to the Earth on its elliptical orbit, resulting in the largest apparent size of the moon's disk as seen from Earth. The technical name is the perigee-syzygy of the Earth-Moon-Sun system.
"Supermoon" officially arrived at about 7 a.m. Eastern Daylight Time Sunday morning, with the moon making its closest swing by Earth this year. About a half hour later, the moon reached full status, making it appear 12 percent larger and 30 percent brighter than a regular full moon.
Don't worry if you missed it. The effect should still linger for a few nights, meaning Sunday, Monday, and even Tuesday should give a good sense of this year's supermoon.