A supermoon is what we call a phenomenon that happens when the Moon is full, positioned on the reverse side of the Earth from the Sun, and when it is as close to the planet as it can be. When all three of those criteria are fulfilled, we get a supermoon. Scientifically, when the Moon is on the opposite side of the Earth from the Sun is called syzygy. When the Moon is at its closest to Earth is called perigee.
The term used by scientists for a supermoon is a combination of those two words - sperigee syzygy. Supermoon, as a term, does not come from astronomy but rather astrology.
How Does A Supermoon Appear?
For a supermoon to occur, two ingredients are of the utmost importance. Firstly the Moon needs to be closest to the Earth in its orbit. It also needs to be at the full phase. A full moon can be seen once every 29.5 days, and the Moon's orbit lasts for 27 days, so it isn't very easy for these two things to align. Once this is set, it is also important that the Sun and Moon are aligned on opposite sides of the Earth. Once all of these conditions are in place, a supermoon is visible in the sky.
For these three things to happen at the same time is a huge coincidence. The positioning of the Moon on the opposite side of Earth as the Sun, and as close to the planet as it can come, while also being full is an event that happens very rarely. Sometimes we only see a supermoon once a year. A supermoon can be up to 30% brighter and 14% larger than a full moon when it is further away from the Earth.
The Astrological Origins Of The Supermoon
The term supermoon was first coined n 1979 by an American astrologist called Richard Nolle. He believed that this phenomenon would be the cause of natural disasters, a claim that was not backed by any scientific data. Some people believe that the appearance of a supermoon can signal upcoming earthquakes. This belief stems from the connection the Moon has with oceanic tides. While that connection is real and scientifically proven, no proof has been found of a supermoon being associated with volcanic eruptions or earthquakes.
Despite this, there is often media speculation of catastrophes being tied to the period leading up to the appearance of a supermoon. Some of the more famous natural disasters that happened around the time of a supermoon are the earthquake and Tsunami in Tōhoku in 2011, and the 2004 Indian Ocean earthquake and tsunami. Scientists have proved the combined effects of the Moon and Sun on the oceans. When the Moon is either full or new, the tides are the highest. Despite all that, this connection isn't strong enough to cause any large scale event, so the possibility of a supermoon being tied to major natural disasters doesn't exist.
There is also a phenomenon called a micromoon, which is the opposite of a supermoon. It happens when the Moon is the farthest point away from the Earth.