Technically speaking, a supermoon refers to the coincidence of a full moon or a new moon with the closest approach the Moon makes to the Earth on its elliptical orbit, resulting in the largest apparent size of the lunar disk as seen from Earth. The association of the Moon with both oceanic and crustal tides has led to claims that the supermoon phenomenon may be associated with increased risk of events such as earthquakes and volcanic eruptions. Continue reading for more.
5. Name Origin
The name SuperMoon was coined by astrologer Richard Nolle in 1979, arbitrarily defined as: "...a new or full moon which occurs with the Moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, Moon and Sun are all in a line, with Moon in its nearest approach to Earth."
The full moon cycle is the period between alignments of the lunar perigee with the sun and the earth, which is about 13.9443 synodic months (about 411.8 days). Thus approximately every 14th full moon will be a supermoon. However, halfway through the cycle the full moon will be close to apogee, and the new moons immediately before and after can be supermoons. Thus there may be as many as three supermoons per full moon cycle.
The combined effect of the Sun and Moon on the Earth's oceans, the tide, is greatest when the Moon is either new or full. At lunar perigee the tidal force is somewhat stronger, resulting in perigean spring tides. But even at its most powerful this force is still relatively weak causing tidal differences of inches at most.
2. Natural Disasters
There has been speculation that natural disasters, such as the 2011 Tōhoku earthquake and tsunami and the 2004 Indian Ocean earthquake and tsunami, are causally linked with the 1-2 week period surrounding a supermoon.
The opposite phenomenon, an apogee-syzygy, has been called a micromoon, though this term is not as widespread as supermoon.