A juxtaposition of the apparent diameters of a more-average full moon on December 20, 2010 (left), and of the supermoon of March 19, 2011 (right) as viewed from Earth.

A supermoon is a full moon or a new moon that nearly coincides with perigee—the closest that the Moon comes to the Earth in its elliptic orbit—resulting in a slightly larger-than-usual apparent size of the Moon as viewed from Earth.[1] The technical name is a perigee syzygy (of the Earth–Moon–Sun system) or a full (or new) Moon around perigee.[a] Because the term supermoon is astrological in origin, it has no precise astronomical definition.[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 like earthquakes and volcanic eruptions, but no such link has been found.[3]

The opposite phenomenon, an apogee syzygy or a full (or new) Moon around apogee, has been called a micromoon.[4]

Definitions

The name supermoon was coined by astrologer Richard Nolle in 1979, in Dell Horoscope magazine 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.

— Richard Nolle[5]
NASA image showing comparison of a supermoon (left) and a micromoon (right)

He came up with the name while reading Strategic Role Of Perigean Spring Tides in Nautical History and Coastal Flooding published in 1976 by NOAA Hydrologist Fergus Wood.[6][7] Nolle explained in 2011 that he based calculations on 90% of the difference in lunar apsis extremes for the solar year. In other words, a full or new moon is considered a supermoon if where is the lunar distance at syzygy, is the lunar distance at the greatest apogee of the year, and is the lunar distance at the smallest perigee of the year.[8][9]

In practice, there is no official or even consistent definition of how near perigee the full Moon must occur to receive the supermoon label, and new moons rarely receive a supermoon label. Different sources give different definitions.[10][11]

NASA image showing comparison of a supermoon (left) and a micromoon (right)

The term perigee-syzygy or perigee full/new moon is preferred in the scientific community.[12] 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. Astrophysicist Fred Espenak uses Nolle's definition but preferring the label of full Moon at perigee, and using the apogee and perigee nearest in time rather than the greatest and least of the year.[13] Wood used the definition of a full or new moon occurring within 24 hours of perigee and also used the label perigee-syzygy.[7]

Wood also coined the less used term proxigee where perigee and the full or new moon are separated by 10 hours or less.[7] Nolle has also added the concept of extreme supermoon in 2000 describing the concept as any new or full moons that are at "100% or greater of the mean perigee".[14]))

Occurrence

Of the possible 12 or 13 full (or new) moons each year, usually three or four may be classified as supermoons, as commonly defined.

The most recent full supermoon occurred on September 29, 2023, and the next one will be on August 19, 2024.[13]

The supermoon of November 14, 2016, was the closest full occurrence since January 26, 1948, and will not be surpassed until November 25, 2034.[15]

The closest full supermoon of the 21st century will occur on December 6, 2052.[16]

Supermoons will be the marked points nearest the bottom of the graph.

The oscillating nature of the distance to the full or new moon is due to the difference between the synodic and anomalistic months.[13] The period of this oscillation is about 14 synodic months, which is close to 15 anomalistic months. So every 14 lunations there is a Full Moon nearest to perigee.

Occasionally, a supermoon coincides with a total lunar eclipse. The most recent occurrence of this by any definition was in May 2022, and the next occurrence will be in October 2032.[13]

In the Islamic calendar, the occurrence of full supermoons follows a seven-year cycle. In the first year, the full moon is near perigee in month 1 or 2, the next year in month 3 or 4, and so on. In the seventh year of the cycle the full moons are never very near to perigee. Approximately every 20 years the occurrences move to one month earlier. At present such a transition is occurring, so full supermoons occur twice in succession. For example in Hijri year 1446, they occur both in month 3 (Rabīʿ al-ʾAwwal, on September 18, 2024) and in month 4 (Rabīʿ ath-Thānī, on October 17, 2024).

Appearance

Further information: Moon illusion

The supermoon of March 19, 2011 (right), compared to an average full moon of January 18, 2011 (left), as viewed from Earth

A full moon at perigee appears roughly 14% larger in diameter than at apogee.[17] Many observers insist that the Moon looks bigger to them. This is likely due to observations shortly after sunset when the Moon appears near the horizon and the Moon illusion is at its most apparent.[18]

While the Moon's surface luminance remains the same, because it is closer to the Earth the illuminance is about 30% brighter than at its farthest point, or apogee. This is due to the inverse square law of light which changes the amount of light received on Earth in inverse proportion to the distance from the Moon.[19] A supermoon directly overhead could provide up to 0.36 lux.[20]

Effects on Earth

Claims that supermoons can cause natural disasters, and the claim of Nolle that supermoons cause "geophysical stress", have been refuted by scientists.[2][21][22][23]

Despite lack of scientific evidence, 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.[24] A large, 7.5 magnitude earthquake centred 15 km north-east of Culverden, New Zealand at 00:03 NZDT on November 14, 2016, also coincided with a supermoon.[25][26] Tehran earthquake on May 8, 2020, also coincided with a supermoon.

Scientists have confirmed that the combined effect of the Sun and Moon on the Earth's oceans, the tide,[27] is greatest when the Moon is either new or full.[28] and that during lunar perigee, the tidal force is somewhat stronger,[29] resulting in perigean spring tides. However, even at its most powerful, this force is still relatively weak,[30] causing tidal differences of inches at most.[31]

Total lunar eclipses

Total lunar eclipses which fall on supermoon and micromoon days are relatively rare. In the 21st century, there are 87 total lunar eclipses, of which 28 are supermoons and 6 are micromoons. Almost all total lunar eclipses in Lunar Saros 129 are micromoon eclipses. An example of a supermoon lunar eclipse is the September 2015 lunar eclipse.

Annular solar eclipses

Annular solar eclipses occur when the Moon's apparent diameter is smaller than the Sun's. Almost all annular solar eclipses between 1880 and 2060 in Solar Saros 144 and almost all annular solar eclipses between 1940 and 2120 in Solar Saros 128 are micromoon annular solar eclipses.[32]

See also

Notes

  1. ^ See perigee and syzygy

References

  1. ^ Staff (September 7, 2014). "Revisiting the Moon". New York Times. Retrieved September 8, 2014.
  2. ^ a b Plait, Phil. "Kryptonite for the supermoon". Bad Astronomy. Discover. Archived from the original on October 22, 2019. Retrieved August 29, 2015.
  3. ^ Rice, Rachel. "No Link Between 'Super Moon' and Earthquakes". Discovery News. Archived from the original on June 13, 2011. Retrieved March 20, 2015.
  4. ^ "What Is a Micromoon?". timeanddate.com. Stavanger, Norway: Time and Date AS. Retrieved August 6, 2018.
  5. ^ Nolle, Richard. "Supermoon". Astropro (No publication date; modified March 10, 2011). Retrieved March 14, 2011.
  6. ^ "What is a Super Moon". Actforlibraries.org. Retrieved January 10, 2018.
  7. ^ a b c Fergus, Wood (1976). The Strategic Role of Perigean Spring Tides in Nautical History and Coastal Flooding, 1635-1976. Washington DC: NOAA.
  8. ^ "November 2017 full moon a supermoon? | EarthSky.org". earthsky.org. Retrieved January 8, 2018.
  9. ^ Nolle, Richard. "SuperMoon: What It Is, What It Means". www.astropro.com. Retrieved January 8, 2018.
  10. ^ "November 2017 full moon a supermoon? | EarthSky.org". earthsky.org. Retrieved January 8, 2018.
  11. ^ Nolle, Richard. "Astrologer Richard Nolle's Century 21 CE SuperMoon Table". www.astropro.com. Retrieved January 8, 2018.
  12. ^ Phillips, Tony (May 2, 2012). "Perigee "Super Moon" On May 5–6". NASA Science News. NASA. Retrieved May 6, 2012.
  13. ^ a b c d Espenak, Fred. "Full Moon at Perigee (Super Moon): 2001 to 2100". astropixels.com. Archived from the original on February 10, 2020. Retrieved March 12, 2020.
  14. ^ "Astrologer Richard Nolle's Century 21 CE SuperMoon Table". www.astropro.com. 2000. Retrieved March 8, 2020.
  15. ^ "What is a supermoon?". Retrieved November 14, 2016.
  16. ^ "Closest supermoon since 1948!". EarthSky. November 12, 2016. Retrieved November 14, 2016.
  17. ^ "Supermoon 2018: When and How to See January's Two Full Moons". Space.com. Retrieved January 10, 2018.
  18. ^ "What Is A Supermoon? Facts vs. Fiction – Sky & Telescope". Sky & Telescope. November 8, 2016. Retrieved January 10, 2018.
  19. ^ Phillips, Tony (March 16, 2011). "Super Full Moon". Science@NASA Headline News. NASA. Archived from the original on May 7, 2012. Retrieved June 22, 2013.
  20. ^ Kyba, Christopher C M; Mohar, Andrej; Posch, Thomas (February 1, 2017). "How bright is moonlight?" (PDF). Astronomy & Geophysics. 58 (1): 1.31–1.32. doi:10.1093/astrogeo/atx025.
  21. ^ "Can the position of the Moon affect seismicity?". The Berkeley Seismological Laboratory. 1999. Retrieved March 14, 2011.
  22. ^ Fuis, Gary. "Can the position of the moon or the planets affect seismicity?" (No publication date). U.S. Geological Survey: Earthquake Hazards Program. Archived from the original on May 7, 2011. Retrieved March 14, 2011.
  23. ^ Wolchover, Natalie (March 9, 2011). "Will the March 19 "SuperMoon" Trigger Natural Disasters?". Life's Little Mysteries. Archived from the original on March 15, 2011. Retrieved March 15, 2011.
  24. ^ Paquette, Mark (March 1, 2011). "Extreme Super (Full) Moon to Cause Chaos?". Astronomy Weather Blog. AccuWeather. Retrieved March 14, 2011.
  25. ^ "GeoNet – Quakes". Retrieved November 13, 2016.
  26. ^ Andrew Griffin. "Supermoon: Biggest in living memory to appear in the sky, as 2016 ends with three huge full moons in a row". The Independent. Archived from the original on May 25, 2022.
  27. ^ Plait, Phil (2008). "Tides, the Earth, the Moon, and why our days are getting longer". Bad Astronomy (Modified March 5, 2011). Retrieved March 14, 2011.
  28. ^ Sumich, J.L. (1996). "Animation of spring and neap tides". NOAA's National Ocean Service. Retrieved June 22, 2013.
  29. ^ "Apogee and Perigee of the Moon". Moon Connection (No publication date). Retrieved March 14, 2011.
  30. ^ Plait, Phil (March 11, 2011). "No, the 'supermoon' didn't cause the Japanese earthquake". Discover Magazine. Archived from the original on October 22, 2019. Retrieved March 14, 2011.
  31. ^ Rice, Tony (May 4, 2012). "Super moon looms Saturday". WRAL-TV. Retrieved May 5, 2012.
  32. ^ "Moon at Perigee and Apogee: 2001 to 2100". astropixels.com. Retrieved November 19, 2018.

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