A Supermoon happens when a Full Moon or New Moon coincides with the Moon's closest approach to Earth; also called perigee. A Super Full Moon looks around 12% to 14% bigger than its counterpart, the Micromoon.
The Supermoon on November 14, 2016, will be the closest a Full Moon has been to Earth since January 26, 1948. The next time a Full Moon is even closer to Earth will be on November 25, 2034 (dates based on UTC time).
A Supermoon can be a Full or New Moon. A Super Full Moon is visible to us, but a Super Full Moon is not.
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.
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.
The following definitions are used at timeanddate.com:
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.
The Full Moon near the horizon looks bigger and brighter than when the same Full Moon is higher in the sky.
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.
The tides on Earth are mostly generated by the Moon's gravitational pull from one side of Earth to the other. The Moon's gravity can cause small ebbs and flows in the continents called land tides or solid Earth tides. These are greatest during the Full and New Moons because the Sun and Moon are aligned on the same or opposite sides of Earth.
When the Moon is closer to Earth, the gravitational pull leads to larger variation between high and low tides. It also causes higher spring tides, known as perigean spring tide or the more colloquial term, king tide. It has nothing to do with the season spring, but rather it is a synonym to jump or leap. King tides may cause abnormally high flooding in coastal areas.
The tides are smaller during Micromoon because the Moon is farther away and the lower gravitational pull leads to a smaller variation between high and low tides, known as neaps or neap tide, from Anglo-Saxon, meaning without the power.
Moon's gravitational pull causes tides.
Although the Sun and the Moon's alignment cause a small increase in tectonic activity, the effects of the Supermoon on Earth are minor. Many scientists have conducted studies, and they haven't found anything significant that can link the Super Moon to natural disasters.
According to NASA, the combination of the Moon being at its closest and at Full Moon, should not affect the internal energy balance of the Earth since there are lunar tides every day.