How Our Moon Becomes A "Supermoon"

A Supermoon happens when a Full Moon or New Moon coincides with the Moon's closest approach to Earth; also called perigee. A Supermoon can be a Full or New Moon. A Super Full Moon looks around 12% to 14% bigger than its counterpart, the Micromoon. How can Full Moon be in the daytime?

Perigee and Apogee

The Moon's orbit around Earth is not a perfect circle, but elliptical, with one side closer to Earth than the other.

As a result of the Moon's elliptical orbit, the distance between the Moon and Earth varies throughout the month and the year. On average the distance is about 382,900 kilometers (238,000 miles).

The point on the Moon's orbit closest to Earth is called the perigee and the point farthest away is the apogee.

When a Full Moon coincides with its closest approach to Earth, it is called a Super Full Moon. A New Moon that takes place when the Moon is around its perigee is known as a Super New Moon.

A Micromoon, on the other hand, is when a Full or a New Moon is farthest from the Earth, around apogee. It's also known as a Minimoon, Mini Full Moon, or a Mini New Moon.

Astronomical terms & definitions
Not an Official Name

Supermoon is not an official astronomical term. It was first coined by an astrologer, Richard Nolle, in 1979. He defined it as ‘a New or a Full Moon that occurs when the Moon is at or near (within 90% of) its closest approach to Earth in its orbit’. It is not clear why he chose the 90% cut off in his definition.

There are no official rules as to how close or far the Moon must be to qualify as a Supermoon or a Micro Moon. Different outlets use different definitions. Due to this, a Full Moon classified as a Supermoon by one source may not qualify as a Super Full Moon by another.

Supermoon: A Full or New Moon that occurs when the center of the Moon is less than 360,000 kilometers (ca. 223,694 miles) from the center of Earth.
Micromoon: A Full Moon or New Moon that takes place when the center of the Moon is farther than 405,000 kilometers (ca. 251,655 miles) from the center of Earth.

Technical Name: Perigee-syzygy

The technical term for a Supermoon is perigee-syzygy of the Earth-Moon-Sun system. In astronomy, the term syzygy refers to the straight-line configuration of three celestial bodies.

When the Moon is close to the lunar nodes of its path during syzygy, it causes a total solar eclipse or a total lunar eclipse.

Because it's so close to Earth, a Super Full Moon looks about 7% bigger than an average Full Moon. When compared to a Micromoon, it looks about 12% to 14% larger.

A Super Full Moon also looks about 30% brighter than a Micro Full Moon and about 16% brighter than an average Full Moon.

Biggest During Winter

At this time of the year, Earth is closer to the Sun. Because of this, the Sun's gravity pulls the Moon closer to Earth, making winter Super Full Moons look bigger.

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