What Is a Supermoon?
A supermoon occurs when the full moon is at or near the part of its orbit that is closest to the earth. The moon's orbit is elliptical with an average distance from the earth is 238,900 miles. At its perigee (the closest approach of its orbit) it could be about 222,000 miles from earth.
The supermoon moniker has detractors because it's not as rare as, say, August's total solar eclipse. Moreover, the difference between an average full moon and a supermoon is noticeable but not massive. With a supermoon, the moon appears about 14% bigger and 30% brighter than when the moon is near its apogee or furthest point of orbit from earth. While that's not the kind of thing causing people to have spiritual awakenings, it is bigger and brighter, so just let us have this, Neil DeGrasse Tyson.
The term supermoon has been around for about 40 years. However, it became popular in 2016 when there were three supermoons in a row, just like you're seeing right now.