WHAT IS SUPERMOON ?
A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the lunar disk as viewed from Earth. . The term supermoon is astrological in origin and has no precise astronomical definition.supermoon" isn't a scientific term. By several accounts, it was first coined back in the late 1970s by an astrologer, Richard Nolle, who defined it as a new or full moon that occurs when the moon is within 90 percent of its closest approach to Earth in a given orbit — 224,641 miles or 361,524 kilometers from the planet. Given the change in distance between the moon’s farthest and closest points, the full moon can appear as much as 14% larger in the sky and 30% brighter to our eyes than at minimum size and brightness.
The technical name of Supermoon is a perigee syzygy (of the Earth–Moon–Sun system) or a full (or new) Moon around perigee .
WHAT CAUSES A SUPERMOON ?
Supermoons happen because the moon doesn't orbit the earth in a perfect circle, but rather in an elliptical path. That means its distance from the Earth can vary in the course of a month, from 252,000 miles at its farthest point, which is called the apogee, to roughly 225,800 miles at its closest approach, which is called the perigee.
But the lunar orbit isn't perfectly regular, either, because it's affected by the sun's gravity. So on some occasions, the moon's perigee is closer than others.
Perigees happen on average every 29.53 days .
But a few times a year, the sun, moon and Earth line up just right, so that a perigee coincides with the most dramatic phases of the moon — the new moon, when the orb is just a sliver — or the full moon. That's when we notice because the moon can appear to be slightly bigger and significantly brighter than normal .


