# Supermoon

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

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 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 never outlined why he chose 90%,[2] but 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 ${\displaystyle ld_{s}\leq ld_{p}+0.1*(ld_{a}-ld_{p})}$ 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.[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. Sky and Telescope magazine refers to full Moon which comes within 223,000 miles (359,000 km), TimeandDate.com prefers a definition of 360,000 kilometres (220,000 mi). EarthSky uses Nolle's definition comparing their calculations to tables published by Nolle in 2000.[10][11]

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.[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]

Other Languages
Afrikaans: Supermaan
العربية: قمر عملاق
বাংলা: সুপারমুন
беларуская (тарашкевіца)‎: Супэрмесяц
भोजपुरी: सुपरमून
català: Superlluna
Deutsch: Supermond
español: Superluna
Esperanto: Superluno
فارسی: ابرماه
français: Super lune
galego: Superlúa
한국어: 슈퍼문
հայերեն: Գերլուսին
हिन्दी: सुपरमून
Bahasa Indonesia: Bulan super
íslenska: Ofurmáni
italiano: Superluna
עברית: ירח-על
Basa Jawa: Supermoon
ქართული: სუპერმთვარე
Kiswahili: Mwezi mpevu sana
latviešu: Supermēness
Limburgs: Supermaon
magyar: Szuperhold
मैथिली: सुपर मुन
മലയാളം: സൂപ്പർമൂൺ
Bahasa Melayu: Fenomena Supermoon
မြန်မာဘာသာ: စူပါမွန်း
Nederlands: Supermaan
नेपाली: सुपर मुन
norsk: Supermåne
português: Superlua
română: SuperLuna
русский: Суперлуние
Scots: Supermuin
српски / srpski: Супермесец
suomi: Superkuu
svenska: Supermåne
українська: Супермісяць
اردو: بدر کامل
Tiếng Việt: Mặt Trăng Lớn