A Field Guide to Full Moons

It appears we have entered an era of moon near-hysteria, with each month bringing about a rush of excited stories detailing the unique charms of whatever full moon is in the works at the time. And while some fatigued journalists will kvetch about the hype, “It’s just a full moon, for heaven’s sake,” I think it’s great. How wonderful that people are excited to go outside, look up to the heavens, and marvel at the beauty of the sky.

That said, it does get confusing; what with this moon and that moon, the supermoons and blood moons and black moons, and you name it. When we start hearing about events like the “super blue blood moon"—what in the world does that mean?

So, to make sense of all the lunacy, we present some basic definitions of the various full moons.

Black Moon

The black sheep of the moon family, a black moon may not be that much to look at, since it’s the second new moon within a month—and since we can’t see new moons, well we’ll just have to appreciate that it’s there. (And while, yes, a new moon isn't exactly a full moon, per se, it is full on the other side where the sun is illuminating it.) Think of it as the esoteric twin of an exuberant supermoon; see below.

Blood Moon

This one comes with a pretty simple description. A blood moon occurs during a lunar eclipse. NASA explains, “While the Moon is in the Earth’s shadow, it will take on a reddish tint, known as a ‘blood moon.’”

Blue Moon

A blue moon occurs when a single month hosts two full moons. The lunar calendar almost lines up with our monthly calendar, but not exactly. The lunar cycle—the time from one new moon to the next—is, on average, 29.53 days. Usually, this means we get one full moon and one new moon each calendar month. But given that our months are generally longer than 29.53 days, it means that once in a blue moon ... we get a blue moon. (Which is about once every 2.7 years.)

Supermoon

Supermoons occur when a full moon happens during perigee, the point in its orbit when it’s closest to Earth. The result can make the moon appear up to 14% larger and 30% brighter than other full moons. Add in a little "moon illusion"—an optical illusion where the moon looks larger when it's near the horizon—and the appearance is, in a word, super!

Harvest Moon

The harvest moon is the full moon closest in date to the autumnal equinox; it is usually the September full moon that takes the title of harvest moon. But if the October full moon is closer to the date of the equinox, she takes the name.

Hunter’s Moon

The hunter’s moon is the full moon following the harvest moon; which means that it is usually in October, except for when the harvest moon occurs in October—then, the hunter’s moon happens in November.

So there you have it. Now, when you see something like a super blue blood moon in the news, you know that it's simply the second full moon of the month that happens to be occurring during perigee at the time of a lunar eclipse! For more, here's a great crash course in all things moon by PBS.