A supermoon is a full moon that occurs when the Moon is relatively close to Earth. The nickname describes two things happening together: the Moon is at the full phase, and it is near a closer part of its orbit. It does not mean the Moon suddenly grows, and it is not a separate kind of lunar phase. The Moon’s phases follow a repeating pattern, explained in this guide to how the Moon’s phases work.
The term can be useful, as long as it is not taken to promise a spectacular change in the sky. A nearby full moon is larger in apparent diameter and can look brighter than a more distant one, but the difference is gradual. The Moon’s position, the local horizon, weather and camera settings all affect what an observer sees.
Perigee and full moon are separate events
The Moon travels around Earth in an oval-shaped orbit, so its distance changes. The closest point in an orbit is called perigee, and the farthest is apogee. Typical distances are about 363,300 kilometres at perigee and 405,500 kilometres at apogee; the mean Earth–Moon distance is 384,400 kilometres. These are distances from Earth’s centre to the Moon’s centre, not measurements from the ground to the lunar surface.
A full moon, by contrast, is a phase: the Moon’s Earth-facing side is almost fully lit by the Sun. The full phase comes around every 29.53059 days, while the Moon takes 27.32166 days to circle Earth relative to the stars. Because those cycles differ, a full moon does not happen at the same orbital position each time. Sometimes it falls relatively near perigee, and sometimes it is much farther away.
That distinction explains why a full moon is not automatically a supermoon. The two events must occur close enough together for the Moon’s distance to meet a chosen definition. For a worked example, the full moon on 24 December 2026 is listed at 356,927 kilometres, inside this site’s supermoon threshold. Use the moon phase calendar for dates beyond that fixed example.
How much bigger and brighter is it?
Distance changes apparent size by perspective. A nearby object takes up more of your field of view than the same object farther away. Using typical perigee and apogee distances, the Moon’s apparent diameter at perigee is about 12% greater than at apogee. Its apparent disk area is roughly 24% greater. Those comparisons describe the endpoints of typical orbital distances, not the difference between every pair of full moons.
There is also a physical reason a closer full moon can look brighter: sunlight reflected from the Moon spreads over a larger area as it travels to Earth, so less of it reaches a given patch of ground as the distance increases. In an idealized comparison that ignores changes in surface illumination and viewing conditions, brightness varies approximately with the inverse square of distance. At the 360,000-kilometre cutoff used here, a full moon would be about 7% wider and receive roughly 14% more light than one at the mean distance of 384,400 kilometres.
Those figures are not a promise that the Moon will look 7% larger to your unaided eye. The difference between a supermoon and an ordinary full moon can be hard to judge without a direct comparison. A photograph can make it look much more dramatic through a long focal-length lens, a close foreground or careful framing. Images made with different camera settings are not reliable evidence of how much larger the Moon appeared in the sky.
Why supermoon definitions differ
Supermoon is a popular term, not a single formal astronomical category with one definition used everywhere. Some descriptions focus on a full moon close to perigee; others set a distance cutoff or define closeness as a fraction of the Moon’s orbital range. That means different calendars and articles can label different full moons as supermoons without disagreeing about the Moon’s actual position. They may simply be applying different rules.
For consistency, this site defines a supermoon as a full moon closer than 360,000 kilometres from Earth’s centre. That is a specific, comparatively tight cutoff: the typical perigee distance is about 363,300 kilometres, so not every full moon near perigee qualifies. Under the site’s matching definition, a micromoon is a full moon farther than 405,000 kilometres away.
A label is therefore less informative than the distance behind it. When comparing claims, check whether they refer to a full moon, how distance is measured, and what threshold is being applied. Traditional full-moon names, such as Harvest Moon or Hunter’s Moon, describe a different naming tradition rather than distance; see the guide to full-moon names for that separate topic.
A supermoon is not a lunar eclipse
A supermoon does not cause an eclipse. Both involve the geometry of the Sun, Earth and Moon, but an eclipse needs an additional condition: the Moon must pass through Earth’s shadow. The Moon’s orbit is tilted about 5.14 degrees relative to the plane of Earth’s orbit around the Sun, so most full moons pass above or below that shadow. Only when the geometry lines up near an orbital crossing can a lunar eclipse occur.
A close full moon can coincide with an eclipse if the necessary alignment happens, but closeness by itself is not enough. Likewise, an eclipse does not automatically make the Moon a supermoon under a distance-based definition. The lunar eclipse tracker follows eclipse events, which are a separate reason to watch the Moon.
What to look for when observing
The Moon often seems unusually large when it is near the horizon. This familiar impression, called the Moon illusion, is not evidence that the Moon has moved dramatically closer during the evening. The apparent size change caused by its orbit is real, but the horizon effect is a separate perception. A simple observing test is to hold a small object at arm’s length and compare the Moon’s apparent width at different times; avoid judging size from memory alone.
For a useful comparison, look at two full moons photographed from the same location with the same lens and framing, or compare them in a single sequence that includes a clear scale reference. Keep the horizon and foreground out of the comparison if your goal is to judge the lunar disk itself. Atmospheric haze can make a low Moon look orange or red, but that colour comes from light passing through more air, not from the Moon being closer.
The most grounded expectation is a modest change in apparent size and brightness, set by the Moon’s actual distance and softened by viewing conditions. Knowing the distance, rather than relying on the nickname alone, makes a supermoon easier to understand—and helps separate orbital geometry from the ways photographs and perception can exaggerate it.