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(The phrasing "within 90% of its closest approach" is unclear, but [http://www.astropro.com/features/articles/supermoon/#13 an example] on Nolle's website shows that he means that the Earth–Moon distance is in the lowest tenth of its range.)
(The phrasing "within 90% of its closest approach" is unclear, but [http://www.astropro.com/features/articles/supermoon/#13 an example] on Nolle's website shows that he means that the Earth–Moon distance is in the lowest tenth of its range.)


The term ''supermoon'' is not widely accepted or used within the astronomy or scientific community, who prefer the term ''perigee-syzygy''.<ref>{{cite web |last=Ledermann |first=Tug |title={{-'}}Perigee-syzygy' caused full moon to look bigger, brighter in October |url=http://www.highbeam.com/doc/1P1-146006378.html |work=University Wire |accessdate=14 March 2011 |date=November 13, 2007}}</ref> ''[[Perigee]]'' is the point at which the Moon is closest in its orbit to the Earth, and ''[[syzygy]]'' is a [[full moon|full]] or [[new moon]], when the Earth, the Moon and the Sun are aligned. Hence, ''supermoon'' can be regarded as a combination of the two, although they do not perfectly coincide each time.<ref name="HolleSupermoon"/>
The term ''supermoon'' is not widely accepted or used within the astronomy or scientific community, who prefer the term ''perigee-syzygy''.<ref>{{cite web |last=Ledermann |first=Tug |title={{-'}}Perigee-syzygy' caused full moon to look bigger, brighter in October |url=http://www.highbeam.com/doc/1P1-146006378.html |work=University Wire |accessdate=14 March 2011 |date=November 13, 2007}}</ref> ''[[Perigee]]'' is the point at which the Moon is closest in its orbit to the Earth, and ''[[syzygy]]'' is a [[full moon|full]] or [[new moon]], when the Earth, the Moon and the Sun are aligned. Hence, ''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. <ref name="HolleSupermoon"/>


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 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.

Revision as of 22:50, 21 March 2011

A NASA image of the perigee moon of March 19, 2011 over Washington D.C. near the Lincoln Memorial.

A perigee-syzygy of the Earth-Moon-Sun system or "supermoon" is a full or new moon that coincides with a close approach by the Moon to the Earth. 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).[1][2][3]

Definition

The supermoon of March 19, 2011 (right) compared to a more average moon of December 20, 2010 (left)

The name SuperMoon was coined by astrologer Richard Nolle in 1979, 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.[4]

(The phrasing "within 90% of its closest approach" is unclear, but an example on Nolle's website shows that he means that the Earth–Moon distance is in the lowest tenth of its range.)

The term supermoon is not widely accepted or used within the astronomy or scientific community, who prefer the term perigee-syzygy.[5] 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, 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. [4]

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.

Effect on tides

March 2011 supermoon rising over the Atlantic Ocean

The combined effect of the Sun and Moon on the Earth's oceans, the tide,[6] is greatest when the Moon is new or full. At lunar perigee the tidal force is even stronger,[7] resulting in larger high and low tides on average, but even at its most powerful this force is still weak.[2]

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.

File:Supermoon ESO VLT.jpg
Supermoon on ESO's VLT.

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.[4] 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.[8][9] 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.[2]

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.[10][11][12] 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,[13][14][15] suggesting that the claim of a supermoon effect on the incidence of large-scale earthquakes is unjustified.

Dates of supermoons between 1950 and 2050

A supermoon image of March 19, 2011

There are approximately four to six supermoons annually.[4] The following is a list of past and predicted extreme supermoons[13][14]:

  • November 10, 1954
  • November 20, 1972
  • January 8, 1974
  • February 26, 1975
  • December 2, 1990
  • January 19, 1992
  • March 8, 1993
  • January 10, 2005
  • December 12, 2008
  • January 30, 2010
  • March 19, 2011[16]
  • November 14, 2016
  • January 2, 2018
  • January 21, 2023
  • November 25, 2034
  • January 13, 2036

References

  1. ^ Meeus, Jean (1997). Mathematical Astronomy Morsels. Richmond, Virginia: Willmann-Bell. p. 15. ISBN 0-943396-51-4.
  2. ^ a b c Plait, Phil (March 11, 2011). "No, the 'supermoon' didn't cause the Japanese earthquake". Discover Magazine. Retrieved 14 March 2011.
  3. ^ Hawley, John. "Appearance of the Moon Size". Ask a Scientist. Newton. Retrieved 14 March 2011; no publication date. {{cite web}}: Check date values in: |accessdate= (help)
  4. ^ a b c d Nolle, Richard. "Supermoon". Astropro. Retrieved 14 March 2011; no publication date; modified March 10, 2011. {{cite web}}: Check date values in: |accessdate= (help)
  5. ^ Ledermann, Tug (November 13, 2007). "'Perigee-syzygy' caused full moon to look bigger, brighter in October". University Wire. Retrieved 14 March 2011.
  6. ^ Plait, Phil (2008). "Tides, the Earth, the Moon, and why our days are getting longer". Bad Astronomy. Retrieved 14 March 2011; modified March 5, 2011. {{cite web}}: Check date values in: |accessdate= (help)
  7. ^ "Apogee and Perigee of the Moon". Moon Connection. Retrieved 14 March 2011; no publication date. {{cite web}}: Check date values in: |accessdate= (help)
  8. ^ Paquette, Mark (March 1, 2011). "Extreme Super (Full) Moon to Cause Chaos?". Astronomy Weather Blog. AccuWeather. Retrieved 14 March 2011;. {{cite web}}: Check date values in: |accessdate= (help)CS1 maint: extra punctuation (link)
  9. ^ "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.
  10. ^ "Can the position of the moon affect seismicity?". The Berkeley Seismological Laboratory. 1999. Retrieved 14 March 2011.
  11. ^ Fuis, Gary. "Can the position of the moon or the planets affect seismicity?". U.S. Geological Survey: Earthquake Hazards Program. Retrieved 14 March 2011; no publication date. {{cite web}}: Check date values in: |accessdate= (help)
  12. ^ Wolchover, Natalie (March 9, 2011). "Will the March 19 'Supermoon' Trigger Natural Disasters?". Life's Little Mysteries. Retrieved 15 March 2011.
  13. ^ a b Nolle, Richard. "20th Century SuperMoon Alignments". Astropro. Retrieved 14 March 2011; no publication date. {{cite web}}: Check date values in: |accessdate= (help)
  14. ^ a b Nolle, Richard. "21st Century SuperMoon Alignments". Astropro. Retrieved 20 March 2011; no publication date. {{cite web}}: Check date values in: |accessdate= (help)
  15. ^ "Magnitude 8 and Greater Earthquakes Since 1900". Earthquake Hazards Program. U.S. Geological Survey. Retrieved 20 March 2011; no publication date; modified March 11, 2011. {{cite web}}: Check date values in: |accessdate= (help)
  16. ^ Fazekas, Andrew (March 17, 2011). "-'Supermoon': Biggest Full Moon in 18 Years Saturday". National Geographic. Retrieved 20 March 2011.
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