Aurora - Wikipedia Jump to content Main menu Main menu move to sidebar hide Navigation Main page Contents Current events Random article About Wikipedia Contact us Contribute Help Learn to edit Community portal Recent changes Upload file Special pages Search Search Appearance Donate Create account Log in Personal tools Donate Create account Log in Contents move to sidebar hide (Top) 1 Etymology 2 Characterisation Toggle Characterisation subsection 2.1 Altitude 2.2 Forms 2.3 Colours and wavelengths of auroral light 2.4 Changes with time 2.5 Other auroral emissions 2.6 Abnormal types 2.6.1 STEVE 2.6.2 Picket-fence aurora 2.6.3 Dune aurora 2.6.4 Fragments of Aurora-like Emission 2.6.5 Horse-collar aurora 2.6.6 Conjugate auroras 3 Causes Toggle Causes subsection 3.1 Auroral particles 3.2 Auroral particle acceleration 3.3 Atmosphere 3.4 Ionosphere 4 Interaction of the solar wind with Earth Toggle Interaction of the solar wind with Earth subsection 4.1 Magnetosphere 5 Extraterrestrial auroras 6 Historically significant events 7 Historical views and folklore 8 In popular culture 9 See also 10 References 11 Further reading 12 External links Toggle External links subsection 12.1 Multimedia Toggle the table of contents Aurora 103 languages Afrikaans العربية অসমীয়া Asturianu Azərbaycanca تۆرکجه Башҡортса Bikol Central Беларуская (тарашкевіца) Беларуская Български বাংলা Brezhoneg Bosanski Català کوردی Čeština Чӑвашла Cymraeg Dansk Deutsch Ελληνικά Esperanto Español Eesti Euskara فارسی Suomi Võro Føroyskt Français Frysk Gaeilge Gàidhlig Galego Hausa עברית हिन्दी Hrvatski Magyar Հայերեն Արեւմտահայերէն Interlingua Bahasa Indonesia Ido Íslenska Italiano 日本語 Jawa ქართული Қазақша ಕನ್ನಡ 한국어 Latina Lëtzebuergesch Lietuvių Latviešu Македонски മലയാളം Монгол मराठी Bahasa Melayu မြန်မာဘာသာ Nederlands Norsk nynorsk Norsk bokmål Occitan ଓଡ଼ିଆ Polski Piemontèis Nawat پښتو Português Română Русский Саха тыла Sicilianu Scots Srpskohrvatski / српскохрватски Simple English Slovenčina Slovenščina Anarâškielâ Shqip Српски / srpski Seeltersk Svenska Kiswahili தமிழ் తెలుగు ไทย Türkçe Татарча / tatarça Українська اردو Oʻzbekcha / ўзбекча Tiếng Việt Winaray 吴语 文言 閩南語 / Bân-lâm-gí 粵語 中文 Edit links Article Talk English Read Edit View history Tools Tools move to sidebar hide Actions Read Edit View history General What links here Related changes Upload file Permanent link Page information Cite this page Get shortened URL Switch to legacy parser Print/export Download as PDF Printable version In other projects Wikimedia Commons Wikiquote Wikivoyage Wikidata item Appearance move to sidebar hide From Wikipedia, the free encyclopedia (Redirected from Aurora borealis) Atmospheric effect caused by the solar wind Several terms redirect here. For other uses, see Aurora (disambiguation), Aurora Borealis (disambiguation), Aurora Australis (disambiguation), Northern Lights (disambiguation), and Southern Lights (disambiguation). Images of auroras from across the world, including those with rarer red and blue lights An aurora (plural</span>"}]],"parts":[{"template":{"target":{"wt":"plural form","href":"./Template:Plural_form"},"params":{},"i":0}}]}'>pl. aurorae or auroras) is a natural light display in Earth's upper atmosphere caused by charged particles from the Sun colliding with atoms in the atmosphere. These collisions excite oxygen and nitrogen, which then emit light of different colors such as green, red, and purple.[1] When observed in high-latitude regions[2] they are called polar lights and aurora polaris. In the Arctic they are called the northern lights or aurora borealis; in the Antarctic, the term southern lights or aurora australis is used.[3][4] Auroras display dynamic patterns of radiant light that appear as curtains, rays, spirals or dynamic flickers covering the entire sky.[5] Auroras are the result of disturbances in the Earth's magnetosphere caused by enhanced speeds of solar wind from coronal holes and coronal mass ejections. These disturbances alter the trajectories of charged particles in the magnetospheric plasma. These particles, mainly electrons and protons, precipitate into the upper atmosphere (thermosphere/exosphere). The resulting ionization and excitation of atmospheric constituents emit light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Other planets in the Solar System, brown dwarfs, comets, and some natural satellites also host auroras.[6][7] Etymology [edit] The term aurora borealis appeared in a 1649 description by Pierre Gassendi of an auroral display visible all over France in 1621. Gassendi had read the works of Galileo Galilei, who used the term in his extensive writings about aurora in 1619.[8][9] The term entered the English language in 1828.[10] The word aurora is derived from the name of the Roman goddess of the dawn, Aurora, who travelled from east to west announcing the coming of the Sun.[10] Aurora was first used in English in the 14th century.[10] The words borealis and australis are derived from the names of the ancient gods of the north wind (Boreas) and the south wind (Auster or australis) in Greco-Roman mythology.[10] Modern style guides recommend that the names of meteorological phenomena, such as aurora borealis, be uncapitalized.[11] The name "auroras" is now the more common plural in the US;[12] however, aurorae is the original Latin plural and is often used by scientists. In some contexts, aurora is an uncountable noun, multiple sightings being referred to as "the aurora". Characterisation [edit] Earth's night-side upper atmosphere appears from the bottom as bands of afterglow illuminating the troposphere in orange with silhouettes of clouds at the top, and the stratosphere in white and blue at the top of the middle. Next, the mesosphere (pink area) extends to the orange and faintly green line of the lowest airglow, at about one hundred kilometres at the edge of space and the lower edge of the thermosphere (invisible). Continuing with green and red bands of auroras stretching over several hundred kilometres. Auroras are most commonly observed in the "auroral zone",[13] a band approximately 6° (~660 km) wide in latitude centred on 67° north and south.[14] The region that currently displays an aurora is called the "auroral oval". The oval is displaced by the solar wind, pushing it about 15° away from the geomagnetic pole (not the geographic pole) in the noon direction and 23° away in the midnight direction.[14] The peak equatorward extent of the oval is displaced slightly from geographic midnight. It is centred about 3–5° nightward of the magnetic pole so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun, which is called magnetic midnight. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860),[15] and later Hermann Fritz (1881)[16] and Sophus Tromholt (1881)[17] in more detail, established that the aurora appeared mainly in the auroral zone. In northern latitudes, the effect is known as the aurora borealis or the northern lights. The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone.[18] The aurora australis is visible from high southern latitudes in Antarctica, Patagonia, southeastern Australia, New Zealand, and the Falkland Islands. The aurora borealis is visible from areas around the Arctic such as Alaska, Canada, Iceland, Greenland, the Faroe Islands, Scandinavia, Finland, Scotland, and Russia. A geomagnetic storm causes the auroral ovals (north and south) to expand, bringing the aurora to lower latitudes or higher in the south. On rare occasions, the aurora borealis can be seen as far south as the Mediterranean, East Asia, and the southern states of the US, while the aurora australis can be seen as far north as New Caledonia, South Africa, the Pilbara region in Western Australia, and Uruguay.[19] During the Carrington Event, the greatest geomagnetic storm ever observed, auroras were seen even in the tropics. Auroras seen within the auroral oval may be directly overhead. From farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs,[20] which can be subvisual. Videos of the aurora australis taken by the crew of Expedition 28 on board the International Space Station This sequence of shots was taken on 17 September 2011 from 17:22:27 to 17:45:12 GMT, on an ascending pass from south of Madagascar to just north of Australia over the Indian Ocean. This sequence of shots was taken on 7 September 2011 from 17:38:03 to 17:49:15 GMT, from the French Southern and Antarctic Lands in the South Indian Ocean to southern Australia. This sequence of shots was taken on 11 September 2011 from 13:45:06 to 14:01:51 GMT, from a descending pass near eastern Australia, rounding about to an ascending pass to the east of New Zealand. p</sub>]]={{hsp}}3''' corresponds to relatively low levels of geomagnetic activity, while '''[[K-index#The&nbsp;Kp-index and estimated&nbsp;Kp-index|''K''_p]]={{hsp}}9''' represents high levels."},"image1":{"wt":"Aurora Kp Map North America.gif"},"alt1":{"wt":"Kp map of North America"},"caption1":{"wt":"North America"},"image2":{"wt":"Aurora Kp Map Eurasia.gif"},"alt2":{"wt":"Kp map of Eurasia"},"caption2":{"wt":"Eurasia"}},"i":0}}]}'>NOAA maps of North America and Eurasia North America Eurasia These maps show the local midnight equatorward boundary of the aurora at different levels of geomagnetic activity as of 28 October 2011 – these maps change as the location of the geomagnetic poles change. A K-index of Kp= 3 corresponds to relatively low levels of geomagnetic activity, while Kp= 9 represents high levels. Auroras are occasionally seen in latitudes below the auroral zone when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or during the three years after the peak.[21][22] An electron spirals (gyrates) about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the "pitch angle" of the particle. The distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the electron travels to a region of greater field strength nearer to the atmosphere. Thus, it is possible for some particles to return, or mirror, if the angle becomes 90° before entering the atmosphere to collide with the denser molecules there. Other particles that do not mirror enter the atmosphere and contribute to the auroral display over a range of altitudes. Other types of auroras have been observed from space; for example, "poleward arcs" stretching sunward across the polar cap, the related "theta aurora",[23] and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as pulsating aurora, "black aurora" and their rarer companion "anti-black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) is obser…