The Supermoon
A supermoon occurs when a full moon coincides with the perigee of the moon’s orbital cycle. A perigee is the point at which the moon moves closest to Earth during orbit. Because the orbit is not a perfect circle, this means the moon typically sits anywhere between 252,000 and 226,000 miles from Earth. That is a difference of 26,000 miles—longer than the entire circumference of the Earth.
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.
A Super Full Moon looks larger.According to NASA, a Super Full Moon looks around 12% to 14% bigger than a Micromoon.
When a Full Moon coincides with its closest approach to Earth, it is called a Super Full Moon. A New Moonthat takes place when the Moon is around its perigee is known as a Super New Moon.
A 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.) 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.
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.
A Full Moon near the horizon looks bigger and brighter than when the same Full Moon is higher in the Sky.
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.
Supermoons during Northern Hemisphere winter months tend to look larger than Supermoons that occur during the rest of the year. 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 any winter Super Full Moons look bigger than summer Super Full Moons.
The best time to enjoy a Super Full Moon is after moonrise when the Moon is just above the horizon, weather permitting. At this position, a Super Full Moon will look bigger and brighter than when it's higher up in the sky because you can compare the apparent size of the Moon with elements in the landscape like hills, foliage, and buildings. This effect is called the Moon Illusion.