File:Supermoon comparison.jpg

A supermoon is 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.[1] The technical name is the perigee-syzygy of the Earth-Moon-Sun system. The term "supermoon" is not astronomical, but originated in modern astrology.[2] 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, but the evidence of such a link is widely held to be unconvincing.[3]

The most recent occurrence was on September 9, 2014.[4]

The opposite phenomenon, an apogee-syzygy, has been called a micromoon,[5] though this term is not as widespread as supermoon.


The Moon's distance varies each month between approximately Script error and Script error due to its elliptical orbit around the Earth (distances given are center-to-center).[6][7][8]

According to NASA, a full moon at perigee is up to 14% larger (in area, or almost 7% larger diameter) and 30% brighter than one at its farthest point, or apogee.[9]


The name SuperMoon was coined by astrologer Richard Nolle in 1979, arbitrarily defined as: Template:Quote Nolle also claimed that the moon causes "geophysical stress" during the time of a supermoon. Nolle never outlined why the 90% was chosen.[2]

The term supermoon is not used within the astronomical community, which use the term perigee-syzygy or perigee full/new moon.[10] Perigee is the point at which the Moon is closest in its orbit to the Earth, and syzygy is when the Earth, the Moon and the Sun are aligned, which happens at every full or new moon. Hence, a supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time.


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.

Since 13.9443 differs from 14 by very close to Template:Frac, the supermoons themselves will vary with a period of about 18 full moon cycles (about 251 synodic months or 20.3 years). Thus for about a decade the largest supermoons will be full, and for the next decade the largest supermoons will be new.

Effect on tidesEdit

The combined effect of the Sun and Moon on the Earth's oceans, the tide,[11] is greatest when the Moon is either new or full.[12] At lunar perigee the tidal force is somewhat stronger,[13] resulting in perigean spring tides. But even at its most powerful this force is still relatively weak[7] causing tidal differences of inches at most.[14]

As the tidal force follows an inverse-cube law, that force is 19% greater than average. However, because the actual amplitude of tides varies around the world, this may not translate into a direct effect.

It has been claimed that the supermoon of March 19, 2011 was responsible for the grounding of five ships in the Solent in the UK,[15] but such claims are not supported by any evidence.

Natural disastersEdit

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.[16][17] No evidence has been found of any correlation between supermoons with major earthquakes.[18][19][20]



  1. Staff. "Revisiting the Moon", New York Times, September 7, 2014. Retrieved on September 8, 2014.
  2. 2.0 2.1 Kryptonite for the supermoon | Bad Astronomy | Discover Magazine
  3. "No Link Between 'Super Moon' and Earthquakes" at
  4. The next supermoon in 2014 is July 12. on 11 July 2014.
  6. Meeus, Jean (1997). Mathematical Astronomy Morsels. Richmond, Virginia: Willmann-Bell.
  7. 7.0 7.1 Plait, Phil (March 11, 2011). No, the 'supermoon' didn't cause the Japanese earthquake. Discover Magazine. Retrieved on 14 March 2011.
  8. Hawley, John. Appearance of the Moon Size. Ask a Scientist. Newton. Retrieved on 14 March 2011.
  9. Phillips, Tony, Dr. (March 16, 2011). Super Full Moon. Science@NASA Headline News. NASA. Archived from the original on May 7, 2012. Retrieved on 22 June 2013.
  10. Phillips, Tony (May 2, 2012). Perigee "Super Moon" On May 5-6. NASA Science News. NASA. Retrieved on 6 May 2012.
  11. Plait, Phil (2008). Tides, the Earth, the Moon, and why our days are getting longer. Bad Astronomy. Retrieved on 14 March 2011.
  12. Sumich, J.L. (1996). Animation of spring and neap tides. NOAA's National Ocean Service. Retrieved on June 22, 2013.
  13. Apogee and Perigee of the Moon. Moon Connection. Retrieved on 14 March 2011.
  14. Rice, Tony, "Super moon looms Saturday", 4 May 2012. Retrieved on 5 May 2012.
  15. Andy Bloxham (March 21, 2011). Supermoon blamed for stranding five ships in Solent. Retrieved on June 22, 2013.
  16. Paquette, Mark (March 1, 2011). Extreme Super (Full) Moon to Cause Chaos?. Astronomy Weather Blog. AccuWeather. Retrieved on 14 March 2011.
  17. Is the Japanese earthquake the latest natural disaster to have been caused by a supermoon?. The Daily Mail (March 11, 2011). Retrieved on 14 March 2011.
  18. Can the position of the Moon affect seismicity?. The Berkeley Seismological Laboratory (1999). Retrieved on 14 March 2011.
  19. Fuis, Gary. Can the position of the moon or the planets affect seismicity?. U.S. Geological Survey: Earthquake Hazards Program. Retrieved on 14 March 2011.
  20. Wolchover, Natalie (March 9, 2011). Will the March 19 "SuperMoon" Trigger Natural Disasters?. Life's Little Mysteries. Retrieved on 15 March 2011.

External linksEdit

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