# Supermoon

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 lunar disk 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] The term supermoon is astrological in origin and has no precise astronomical definition.[2]

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

The real 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 term supermoon is attributed to astrologer Richard Nolle while reading “Strategic Role Of Perigean Spring Tides in Nautical History and Coastal Flooding published in 1976 by NOAA Hydrologist Fergus Wood.[5][6][7] 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.

### Nolle

Nolle described the concept in a 1979 edition of Dell Horoscope including both full and new moons, but has never outlined why he chose 90% nor has provided a definitive formula for determining if a given full or new moon is "super". The basic 1979 definition read:[2]

... 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, Dell Horoscope Magazine, 1979[8]

Nolle amended his definition in 2000 specifying the distance of a given full or new moon be judged against 90% of the mean distance of perigees. Nolle (incorrectly) referenced

A SuperMoon is a perigee-syzygy, a new or full moon (syzygy) which occurs when the Moon is at 90% or greater of its mean closest approach to Earth (perigee).

— Richard Nolle, 2000, Century 21 CE SuperMoon Table[9]

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

In 2011, Nolle added apogees to consideration explaining that he based calculations on 90% of the difference in lunar apsis extremes for the solar year. EarthSky analyzed Nolle's tables and described the updated definition as a full or new moon is considered a supermoon if ${\displaystyle ld_{s}\leq ld_{p}+0.1*(ld_{a}-ld_{p})}$  where ${\displaystyle ld_{s}}$  is the lunar distance at syzygy, ${\displaystyle ld_{a}}$  is the lunar distance at apogee, and ${\displaystyle ld_{p}}$  is the lunar distance at perigee. Nolle based those the mean apsis extremes referencing (incorrectly) the Wikipedia article on the subject arriving at: [10][11]

any lunation closer than 368,630 km. = SuperMoon.

— Richard Nolle, 2011, Supermoon, What It Is, What It Means[12]

Nolle 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".[13]

### Espenak

The term perigee-syzygy or perigee full/new moon is preferred in the scientific community.[14] 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 on full moons occurring "within 90% of its closest approach to Earth in a given orbit" over Nolle's calculations based on the closest of all orbits during the solar year.[15] Wood used the definition of a full or new moon occurring within 24 hours of perigee and also used the label perigee-syzygy.[7]

### Other definitions

Sky and Telescope magazine chose a definition of 223,000 miles (358,884 km).[16]

TimeandDate.com prefers a definition of 360,000 kilometres (223,694 mi). [17]

EarthSky uses Nolle's definition comparing their calculations to tables published by Nolle in 2000.[18][13]

Wood also coined the less used term proxigee where perigee and the full or new moon are separated by 10 hours or less.[7]

## 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 May 7, 2020, and the next one will be on March 28, 2021.[15] The one on November 14, 2016 was the closest full supermoon since January 26, 1948, and will not be surpassed until November 25, 2034.[19] The closest full supermoon of the 21st century will occur on December 6, 2052.[20]

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.[15] 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 was in January 2019 (same moon diameter as the total solar eclipse of December 5, 2048), and the next will be in May 2021 (same moon diameter as the total solar eclipse of July 11, 1991).[15]

## Appearance

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.[21] Many observers insist that the moon looks bigger to them. This is likely due to observations shortly after sunset when the moon is near the horizon and the moon illusion is at its most apparent.[22]

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.[23] A supermoon directly overhead could provide up to 0.36 lux.[24]

## 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.[25][26][27][28]

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.[29] 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.[30][31] 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,[32] is greatest when the Moon is either new or full.[33] and that during lunar perigee, the tidal force is somewhat stronger,[34] resulting in perigean spring tides. However, even at its most powerful, this force is still relatively weak,[35] causing tidal differences of inches at most.[36]

## 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.

## 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.[37]

## 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. Retrieved August 29, 2015.
3. ^ Rice, Rachel. "No Link Between 'Super Moon' and Earthquakes". Discovery News. Retrieved March 20, 2015.
4. ^ "What Is a Micromoon?". timeanddate.com. Stavanger, Norway: Time and Date AS. Retrieved August 6, 2018.
5. ^ Nolle, Richard. "The SuperMoon and Other Lunar Extremes". Mountain Astrologer. Oct/Nov 2007: 20–21.
6. ^ "What is a Super Moon". Actforlibraries.org. Retrieved 2018-01-10.
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. ^ Nolle, Richard. "Supermoon". Astropro (No publication date; modified March 10, 2011). Retrieved 14 March 2011.
9. ^ "Astrologer Richard Nolle's Century 21 CE SuperMoon Table". www.astropro.com. Retrieved 2020-03-08.
10. ^ "November 2017 full moon a supermoon? | EarthSky.org". earthsky.org. Retrieved 2018-01-08.
11. ^ Nolle, Richard. "SuperMoon: What It Is, What It Means". www.astropro.com. Retrieved 2018-01-08.
12. ^ "Supermoon, What It Is, What It Means". www.astropro.com. Retrieved 2020-03-08.
13. ^ a b Nolle, Richard. "Astrologer Richard Nolle's Century 21 CE SuperMoon Table". www.astropro.com. Retrieved 2018-01-08.
14. ^ Phillips, Tony (May 2, 2012). "Perigee "Super Moon" On May 5–6". NASA Science News. NASA. Retrieved 6 May 2012.
15. ^ a b c d Espenak, Fred. "Full Moon at Perigee (Super Moon): 2001 to 2100". astropixels.com. Retrieved 2020-03-12.
16. ^ "What is a Supermoon? Facts vs. Fiction". Sky & Telescope. 2016-11-08. Retrieved 2020-03-08.
17. ^ "Super Full Worm Moon Lights Up the March Sky". www.timeanddate.com. Retrieved 2020-03-08.
18. ^ "November 2017 full moon a supermoon? | EarthSky.org". earthsky.org. Retrieved 2018-01-08.
19. ^ "What is a supermoon?". Retrieved 14 November 2016.
20. ^ "Closest supermoon since 1948!". EarthSky. Retrieved 14 November 2016.
21. ^ "Supermoon 2018: When and How to See January's Two Full Moons". Space.com. Retrieved 2018-01-10.
22. ^ "What Is A Supermoon? Facts vs. Fiction - Sky & Telescope". Sky & Telescope. 2016-11-08. Retrieved 2018-01-10.
23. ^ Phillips, Tony (March 16, 2011). "Super Full Moon". Science@NASA Headline News. NASA. Archived from the original on May 7, 2012. Retrieved 22 June 2013.
24. ^ Kyba, Christopher C M; Mohar, Andrej; Posch, Thomas (1 February 2017). "How bright is moonlight?". Astronomy & Geophysics. 58 (1): 1.31–1.32. doi:10.1093/astrogeo/atx025.
25. ^ "Kryptonite for the supermoon - Bad Astronomy". Bad Astronomy. 2011-03-18. Retrieved 2018-01-07.
26. ^ "Can the position of the Moon affect seismicity?". The Berkeley Seismological Laboratory. 1999. Retrieved 14 March 2011.
27. ^ 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 7 May 2011. Retrieved 14 March 2011.
28. ^ Wolchover, Natalie (March 9, 2011). "Will the March 19 "SuperMoon" Trigger Natural Disasters?". Life's Little Mysteries. Retrieved 15 March 2011.
29. ^ Paquette, Mark (March 1, 2011). "Extreme Super (Full) Moon to Cause Chaos?". Astronomy Weather Blog. AccuWeather. Retrieved 14 March 2011.
30. ^ "GeoNet - Quakes". Retrieved 13 November 2016.
31. ^
32. ^ 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.
33. ^ Sumich, J.L. (1996). "Animation of spring and neap tides". NOAA's National Ocean Service. Retrieved June 22, 2013.
34. ^ "Apogee and Perigee of the Moon". Moon Connection (No publication date). Retrieved 14 March 2011.
35. ^ Plait, Phil (March 11, 2011). "No, the 'supermoon' didn't cause the Japanese earthquake". Discover Magazine. Retrieved 14 March 2011.
36. ^ Rice, Tony (4 May 2012). "Super moon looms Saturday". WRAL-TV. Retrieved 5 May 2012.
37. ^ "Moon at Perigee and Apogee: 2001 to 2100". astropixels.com. Retrieved 2018-11-19.