What is a micromoon?
Quick Answer: A micromoon is a full (or new) moon that happens when the Moon is near apogee, the farthest point from Earth in its elliptical orbit, making it look slightly smaller and dimmer than usual.
The Moon does not circle Earth in a perfect ring. Its orbit is an ellipse, so its distance changes throughout the month. At apogee the Moon sits roughly 406,700 km away, while at perigee it comes as close as about 356,500 km. A full moon at apogee is a micromoon, and it is the exact opposite of a supermoon, which occurs at perigee.
Compared with a supermoon, a micromoon appears about 14% smaller and up to 30% dimmer. Despite those numbers, the change is very hard to notice with the naked eye, since you have no side-by-side reference in the sky. Keep in mind that micromoon is a popular nickname rather than an official astronomical term.