Scientists Say: Supermoon

Supermoon (noun, “SOOP-er-moon”)

A supermoon is a full moon that appears larger and brighter than usual. It occurs when the moon is full and at its closest point to Earth. The word can also refer to a new moon — normally not visible — that occurs when Earth and the moon are closest together.

Our moon doesn’t remain at a constant distance from Earth. That’s because it orbits Earth in the shape of an ellipse — like a squashed oval. Sometimes the moon’s orbit takes it farther away. Sometimes it draws the moon closer. When the moon swings closer to Earth, it can appear larger than usual. Sometimes this event coincides with phases of the moon that amplify the effect.

A supermoon comes in two forms: a full supermoon and a new supermoon. Both happen when the moon comes within about 90 percent of its closest point to Earth. This point — when the moon’s orbit is closest to Earth — is called perigee. When it’s so close to Earth, the moon’s disk is about 14 percent larger in the sky than normal.

The moon makes no light of its own. What we call moonlight is actually sunlight reflecting off the moon’s surface. A full moon is when the side of the moon facing Earth is completely lit up. It looks like a full circle, or disk. When a supermoon occurs during a full moon, astronomers call it a full supermoon. With the moon’s fully illuminated disk looking supersized, it really stands out in the night sky.

A new moon occurs when the side of the moon facing Earth is not lit up, so we cannot see it at night. When a supermoon occurs during a new moon, scientists call it a new supermoon.

In a sentence

Particles ejected from an Indonesian volcano painted a 2019 supermoon with rosy-red hues.

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