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The supermoon of March 19, 2011 (right), compared to a more average moon of December 20, 2010 (left), as viewed from Earth
The March 19, 2011, supermoon was 356,577 kilometers (221,567 miles) away from Earth. The last time the full moon approached so close to Earth was in 1993. It was about 30 percent brighter and 14 percent bigger than a full moon in apogee.

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 opposite phenomenon, an apogee-syzygy, has been called a micromoon,[4] though this term is not as widespread as supermoon.

Occasionally, a supermoon coincides with a total lunar eclipse. The most recent occurrence of this was on September 27–28, 2015, while the next time will be in 2033.[5]


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 centre-to-centre).[6][7][8]

A full moon at perigee is visually larger up to 14% in diameter (or about 30% in area) and shines 30% more light than one at its farthest point, or apogee.[9]


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.[10]

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 uses the term perigee-syzygy or perigee full/new moon.[11] 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 118, 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 tides[edit]

The combined effect of the Sun and Moon on the Earth's oceans, the tide,[12] is greatest when the Moon is either new or full.[13] At lunar perigee the tidal force is somewhat stronger,[14] 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.[15]

As the tidal force follows an inverse-cube law, that force is 19% greater than average.[citation needed] 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,[16] but such claims are not supported by any evidence.

Natural disasters[edit]

There has been media 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.[17][18] No evidence has been found of any correlation between supermoons with major earthquakes.[19][20][21]

Image gallery[edit]


  1. ^ Staff (September 7, 2014). "Revisiting the Moon". New York Times. Retrieved September 8, 2014. 
  2. ^ a b Phil Plait. "Kryptonite for the supermoon". Bad Astronomy. Discover. Retrieved August 29, 2015. 
  3. ^ Rachel Rice. "No Link Between 'Super Moon and Earthquakes". Discovery News. Retrieved March 20, 2015. 
  4. ^ What is a micromoon?, accessed 1 Oct 2015.
  5. ^ "'Supermoon' coincides with lunar eclipse". BBC News. 28 September 2015. Retrieved 29 September 2015. 
  6. ^ Meeus, Jean (1997). Mathematical Astronomy Morsels. Richmond, Virginia: Willmann-Bell. p. 15. ISBN 0-943396-51-4. 
  7. ^ a b Plait, Phil (March 11, 2011). "No, the 'supermoon' didn't cause the Japanese earthquake". Discover Magazine. Retrieved 14 March 2011. 
  8. ^ Hawley, John. "Appearance of the Moon Size". Ask a Scientist (No publication date). Newton. Retrieved 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 22 June 2013. 
  10. ^ Nolle, Richard. "Supermoon". Astropro (No publication date; modified March 10, 2011). Retrieved 14 March 2011. 
  11. ^ Phillips, Tony (May 2, 2012). "Perigee "Super Moon" On May 5–6". NASA Science News. NASA. Retrieved 6 May 2012. 
  12. ^ Plait, Phil (2008). "Tides, the Earth, the Moon, and why our days are getting longer". Bad Astronomy (Modified March 5, 2011). Retrieved 14 March 2011. 
  13. ^ Sumich, J.L. (1996). "Animation of spring and neap tides". NOAA's National Ocean Service. Retrieved June 22, 2013. 
  14. ^ "Apogee and Perigee of the Moon". Moon Connection (No publication date). Retrieved 14 March 2011. 
  15. ^ Rice, Tony (4 May 2012). "Super moon looms Saturday". WRAL-TV. Retrieved 5 May 2012. 
  16. ^ Andy Bloxham (March 21, 2011). "Supermoon blamed for stranding five ships in Solent". Retrieved June 22, 2013. 
  17. ^ Paquette, Mark (March 1, 2011). "Extreme Super (Full) Moon to Cause Chaos?". Astronomy Weather Blog. AccuWeather. Retrieved 14 March 2011. 
  18. ^ "Is the Japanese earthquake the latest natural disaster to have been caused by a supermoon?". The Daily Mail. March 11, 2011. Retrieved 14 March 2011. 
  19. ^ "Can the position of the Moon affect seismicity?". The Berkeley Seismological Laboratory. 1999. Retrieved 14 March 2011. 
  20. ^ Fuis, Gary. "Can the position of the moon or the planets affect seismicity?" (No publication date). U.S. Geological Survey: Earthquake Hazards Program. Retrieved 14 March 2011. 
  21. ^ Wolchover, Natalie (March 9, 2011). "Will the March 19 "SuperMoon" Trigger Natural Disasters?". Life's Little Mysteries. Retrieved 15 March 2011. 

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