“The supermoon is a 16-inch pizza compared with a 15-inch pizza. It’s a slightly bigger moon; I ain’t using the adjective ‘supermoon.'” -Neil deGrasse Tyson
Earlier this month, the full Moon was the first “Supermoon” we’ve seen all year, where the bright full Moon coincided nearly perfectly with perigee, or the Moon’s closest approach to Earth. Yet it won’t be the last: November’s and December’s full Moons will also be Supermoons, appearing up to 14% bigger and 30% brighter than the full Moons from, say, March and April of this year.
This isn’t a rarity, either: Supermoons always come in a row, and we usually get three in a row at that. Moreover, they don’t happen at the same time every year, but appear on a cycle that’s 411 days long. What’s the cause of this, and why does the Moon behave as it does?