Questions and bridges

What Is a Supermoon?

A supermoon is a full (or new) Moon that happens close to perigee, the point where the Moon’s orbit brings it nearest to Earth. It can look slightly larger and brighter than usual, though the difference is subtle to the naked eye. The word is popular rather than strictly scientific.

The short answer

A supermoon is a full Moon that occurs near perigee (the closest point of the Moon’s orbit to Earth). The orbit is an ellipse, not a circle, so the distance changes over each month. When a full Moon coincides with a close approach, it appears a bit bigger and brighter.

How big is the difference?

According to NASA, at best the Moon looks up to about 14% wider and up to about 30% brighter than the smallest full Moon, which happens near apogee (the farthest point). With nothing to compare it to in the sky, most people barely notice. A Moon low on the horizon looks especially large because of the moon illusion, a perceptual effect rather than an astronomical one.

Is it a scientific term?

The word “supermoon” came from astrology in the 1970s and is now widely used in news. Astronomers more often say “perigee full Moon”. There is no single official cutoff for how close counts, so the number of supermoons per year depends on the threshold you choose.

How to enjoy one

No equipment is needed. Step outside at moonrise and compare it with photos from other full Moons. Read more about the Moon, lunar phases and the blue moon.

In the astrological tradition, the full Moon is a time of culmination and awareness, and a supermoon is sometimes described as a more intense version of that theme. This is a cultural interpretation for reflection, not a proven effect.

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