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, or perigee, leading to the technical name for a supermoon of the perigee-syzygy of the Earth-Moon-Sun system. 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. However, the evidence of such a link is widely held to be unconvincing.
The Moon's distance varies each month between approximately 357,000 kilometers (222,000 mi) and 406,000 km (252,000 mi) due to its elliptical orbit around the Earth (distances given are center-to-center).
The size and brightness of an object follows an inverse-square law, which means that a full moon at perigee is 12% larger and brighter than an average full moon. However, because the offset of the moon's orbit versus its phases is only two days, this change in appearance is gradual from month to month and therefore is not usually noticeable to a casual observer.
The name SuperMoon was coined by astrologer Richard Nolle in 1979, defined as:
The term supermoon is not widely accepted or used within the astronomy or scientific community, who prefer the term perigee-syzygy. Perigee is the point at which the Moon is closest in its orbit to the Earth, and syzygy is a full or new moon, when the Earth, the Moon and the Sun are aligned. Hence, a supermoon can be regarded as a combination of the two, although they do not perfectly coincide each time. Syzygy may occur within a maximum of 12 hours from perigee during a supermoon, and 1 hour from perigee during an extreme supermoon.
 Effect on tides
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 even stronger, resulting in larger high and low tides on average, but even at its most powerful this force is still weak causing tidal differences of inches at most.
As the tidal force follows an inverse-cube law, that force is 18% greater than average. However, because the actual amplitude of tides varies around the world, this may not translate into a direct effect.
 Speculative link to natural disasters
Richard Nolle has argued that within ±3 days of a supermoon, the Earth is more subject to natural disasters such as earthquakes and volcanic activity due to the Moon's increased gravitational force. Speculations have moved the goalposts to within 1 or 2 weeks of a supermoon to suggest a causal relationship with specific natural disasters such as the 2011 Tōhoku earthquake and tsunami and the 2004 Indian Ocean earthquake and tsunami. Such a widening of the effect window is unjustified as in both cases the Moon was farther from the Earth than average, making a supermoon effect impossible.
Some studies have reported a weak correlation between lunar activity and shallow, very low intensity earthquakes. However, no evidence has been found of any correlation with major earthquakes. Unjustified claims that the lunar tides trigger earthquakes are rooted in a lack of appreciation that the stress in the Earth is described by a tensor with six independent parameters and that earthquakes occur as slip on existing, weak fault planes. Any change in stress, by lunar tides, by impounding a reservoir, or by a large nearby earthquake, changes the local stress tensor in specific directions. If one wishes to estimate whether a given change advances or hinders slip on a fault, one has to know the orientation of the fault. It is equally likely that the change of the stress due to the moon clamps the fault shut, rather than advancing slip on it. This is why Ohtake has carefully considered the orientation of the fault planes in earthquakes that he showed were correlated with lunar tides.
The 2011 Tōhoku earthquake and tsunami is the only earthquake of 8.0 magnitude or greater to have occurred within 2 weeks of the 14 extreme supermoons from 1900 to the present date, suggesting that the claim of a supermoon effect on the incidence of large-scale earthquakes is unjustified.
- ^ http://news.discovery.com/earth/super-moon-earthquake-no-link-110318.html
- ^ Meeus, Jean (1997). Mathematical Astronomy Morsels. Richmond, Virginia: Willmann-Bell. p. 15. ISBN 0-943396-51-4.
- ^ a b c Plait, Phil (March 11, 2011). "No, the 'supermoon' didn't cause the Japanese earthquake". Discover Magazine. http://blogs.discovermagazine.com/badastronomy/2011/03/11/no-the-supermoon-didnt-cause-the-japanese-earthquake/. Retrieved 14 March 2011.
- ^ Hawley, John. "Appearance of the Moon Size". Ask a Scientist. Newton. http://www.newton.dep.anl.gov/askasci/phy99/phy99371.htm. Retrieved 14 March 2011; no publication date.
- ^ a b c Nolle, Richard. "Supermoon". Astropro. http://www.astropro.com/features/articles/supermoon/. Retrieved 14 March 2011; no publication date; modified March 10, 2011.
- ^ Plait, Phil (2008). "Tides, the Earth, the Moon, and why our days are getting longer". Bad Astronomy. http://www.badastronomy.com/bad/misc/tides.html. Retrieved 14 March 2011; modified March 5, 2011.
- ^ "Apogee and Perigee of the Moon". Moon Connection. http://www.moonconnection.com/apogee_perigee.phtml. Retrieved 14 March 2011; no publication date.
- ^ Rice, Tony (4 May 2012). "Super moon looms Saturday". WRAL-TV. http://www.wral.com/weather/blogpost/11061791/. Retrieved 5 May 2012.
- ^ Supermoon blamed for stranding five ships in Solent” at.telegraph.co.uk, retrieved 23 March 2011
- ^ Paquette, Mark (March 1, 2011). "Extreme Super (Full) Moon to Cause Chaos?". Astronomy Weather Blog. AccuWeather. http://www.accuweather.com/blogs/astronomy/story/46417/extreme-super-full-moon-to-cause-chaos.asp. Retrieved 14 March 2011;.
- ^ "Is the Japanese earthquake the latest natural disaster to have been caused by a supermoon?". The Daily Mail. March 11, 2011. http://www.dailymail.co.uk/sciencetech/article-1365225/Japan-earthquake-tsunami-Did-supermoon-cause-todays-natural-disaster.html. Retrieved 14 March 2011.
- ^ "Can the position of the Moon affect seismicity?". The Berkeley Seismological Laboratory. 1999. http://seismo.berkeley.edu/faq/planets.html. Retrieved 14 March 2011.
- ^ Fuis, Gary. "Can the position of the moon or the planets affect seismicity?". U.S. Geological Survey: Earthquake Hazards Program. http://earthquake.usgs.gov/learn/faq/?faqID=109. Retrieved 14 March 2011; no publication date.
- ^ Wolchover, Natalie (March 9, 2011). "Will the March 19 "SuperMoon" Trigger Natural Disasters?". Life's Little Mysteries. http://www.lifeslittlemysteries.com/will-supermoon-cause-earthquake-storm-natural-disasters-1442/. Retrieved 15 March 2011.
- ^ Ohtake, M. & Tsuruoka, H. (1995). Tidal effect on earthquake occurrence, Kagaku, 65, 285-287.
- ^ Nolle, Richard. "20th Century "SuperMoon" Alignments". Astropro. http://www.astropro.com/features/tables/cen20ce/suprmoon.html. Retrieved 14 March 2011; no publication date.
- ^ Nolle, Richard. "21st Century "SuperMoon" Alignments". Astropro. http://www.astropro.com/features/tables/cen21ce/suprmoon.html. Retrieved 20 March 2011; no publication date.
- ^ "Magnitude 8 and Greater Earthquakes Since 1900". Earthquake Hazards Program. U.S. Geological Survey. http://earthquake.usgs.gov/earthquakes/eqarchives/year/mag8/magnitude8_1900_date.php. Retrieved 20 March 2011; no publication date; modified March 11, 2011.
 External links
Look up supermoon in Wiktionary, the free dictionary.
Wikimedia Commons has media related to: Supermoon
- CBC News, Gallery of the March 19, 2011 supermoon, viewed from across Canada
- BBC News, Gallery of shared pictures
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