A supermoon is a full moon that lines up with the Moon’s closest approach to Earth, making it look a little bigger and noticeably brighter than an ordinary full moon. At its best, a supermoon can appear up to 14% larger and about 30% brighter than the most distant full moon of the year. That’s the whole idea in a sentence.
But there’s a lot of hype wrapped around that simple fact, and a fair amount of confusion too. So let’s separate the real science from the headlines: what actually makes a moon “super,” how much of a difference you can genuinely see, and when you can catch the next one.
What Exactly Makes a Moon “Super”
The key is that the Moon’s orbit around Earth isn’t a perfect circle. It’s a slight oval, so the Moon’s distance from us changes as it goes around. Its closest point is called perigee, and its farthest is apogee.
A supermoon happens when a full moon lands at or near perigee, so we get a full moon that’s also about as close to Earth as it ever gets. When the opposite occurs and a full moon falls near apogee, we get the far less celebrated “micromoon.”
| Detail | Figure |
|---|---|
| Closest point (perigee) | about 363,300 km (226,000 mi) |
| Farthest point (apogee) | about 405,500 km (251,000 mi) |
| Size vs. a distant full moon | up to 14% larger |
| Brightness vs. a distant full moon | about 30% brighter |
| How often | 3 to 4 times a year |
The reason we don’t get a supermoon every single month is that the Moon’s orbit slowly shifts orientation as Earth travels around the Sun. For most of the year, the full moon and perigee simply don’t line up.
How Much Bigger and Brighter, Really?
Here’s where honesty matters, because the headlines oversell it.
That “14% bigger and 30% brighter” figure compares a supermoon to the smallest, most distant full moon of the entire year. Stacked against an ordinary, average full moon, a supermoon is only about 7% wider and 15% brighter. And the blunt truth is that you cannot see a 7% size difference with your naked eye. Without two photos taken side by side at the same zoom, you’d never spot it.
The extra brightness is a little easier to notice, but even that is subtle. So if you’ve ever gone outside for a supermoon and thought “it just looks like a normal full moon,” you weren’t wrong. What really makes a rising full moon look jaw-droppingly huge is a completely separate effect called the Moon illusion, an optical trick of our brains that makes the Moon near the horizon seem gigantic. That happens at every full moon, super or not.
Where the Word “Supermoon” Even Came From
Here’s a fact that surprises people: “supermoon” isn’t an astronomy term at all. Astronomers usually just call it a perigee full moon.
The word was coined in 1979 by an astrologer named Richard Nolle, who defined a supermoon as a full or new moon that falls within 90% of the Moon’s closest approach to Earth. The catchy name stuck, the media ran with it, and now it’s everywhere. That astrological origin is exactly why some astronomers roll their eyes at the term, and why different sources sometimes disagree on how many supermoons a given year has, since there’s no single official cutoff. Worth remembering: the science of the Moon belongs to astronomy, not astrology. If eye-catching lunar events are your thing, our guide to what a blood moon is covers another dramatic one worth chasing.
A supermoon rising near the Lincoln Memorial in Washington, D.C. Near the horizon, a full moon always looks enormous, thanks to a separate trick of the eye. (Image: NASA/Bill Ingalls)
Do Supermoons Actually Affect Earth?
Mostly, no, at least not in the way tabloids suggest. There’s no credible evidence that supermoons trigger earthquakes, disasters, or waves of strange behavior. The old link between the Moon and “lunacy” is folklore, not science.
There is one genuine, gentle effect, though. Because the Moon is closer than usual, its gravity tugs a bit harder on our oceans, producing slightly higher-than-normal tides for a few days. Coastal areas might notice marginally bigger high tides, sometimes called perigean spring tides. It’s real, but it’s modest. To appreciate why the Moon has this pull on us in the first place, our piece on what makes our Moon so special is a good companion read.
When Is the Next Supermoon?
Supermoons come in a little cluster of three or four each year, arriving in consecutive months. According to NASA, the next supermoons fall on November 24 and December 24, 2026, with that December full moon being the closest of the bunch. Because the exact dates shift from year to year, the easiest way to stay ahead of them is to check a running tracker. Our Moon phase and supermoon calculator will tell you what the Moon is doing on any night you like, and NASA keeps its own tidy list on its supermoons page.
Here’s the best advice for actually enjoying one: don’t hunt for a dramatic size difference, because you won’t see it. Instead, catch the supermoon as it rises just above the horizon, when the Moon illusion is working its magic and the golden light is at its most beautiful. That’s when a supermoon truly earns its name, not because of physics, but because of the view.
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