![Aurora australis ISS](https://upload.wikimedia.org/wikipedia/commons/5/52/Aurora_australis_ISS.jpg)
An aurora (plural: auroras or aurorae), also commonly known as the polar lights, is a natural light display in
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
's sky, predominantly seen in
high-latitude regions (around the
Arctic
The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
and
Antarctic
The Antarctic ( or , American English also or ; commonly ) is a polar region around Earth's South Pole, opposite the Arctic region around the North Pole. The Antarctic comprises the continent of Antarctica, the Kerguelen Plateau and other ...
). Auroras display dynamic patterns of brilliant lights that appear as curtains, rays, spirals, or dynamic flickers covering the entire sky.
Auroras are the result of disturbances in the
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
caused by the
solar wind. Major disturbances result from enhancements in the speed of the solar wind from
coronal holes
A coronal hole is a temporary region of relatively cool, less dense plasma (physics), plasma in the solar corona where the Sun's magnetic field extends into interplanetary space as an open field.Freedman, Roger A., and William J. Kaufmann III. "Ou ...
and
coronal mass ejections
A coronal mass ejection (CME) is a significant release of plasma (physics), plasma and accompanying magnetic field from the Sun's Solar corona, corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar ac ...
. These disturbances alter the trajectories of
charged particles in the magnetospheric plasma. These particles, mainly
electron
The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family,
and are generally thought to be elementary particles because they have no kn ...
s and
proton
A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...
s,
precipitate into the upper atmosphere (
thermosphere
The thermosphere is the layer in the Earth's atmosphere directly above the mesosphere and below the exosphere. Within this layer of the atmosphere, ultraviolet radiation causes photoionization/photodissociation of molecules, creating ions; the ...
/
exosphere
The exosphere ( grc, ἔξω "outside, external, beyond", grc, σφαῖρα "sphere") is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the densit ...
). 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.
Most of the
planet
A planet is a large, rounded astronomical body that is neither a star nor its remnant. The best available theory of planet formation is the nebular hypothesis, which posits that an interstellar cloud collapses out of a nebula to create a you ...
s in the
Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
, some
natural satellites,
brown dwarf
Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
s, and even
comet
A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
s also host auroras.
Etymology
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. Ancient Greek poets used the corresponding name
Eos
In ancient Greek mythology and religion, Eos (; Ionic and Homeric Greek ''Ēṓs'', Attic ''Héōs'', "dawn", or ; Aeolic ''Aúōs'', Doric ''Āṓs'') is the goddess and personification of the dawn, who rose each morning from her home ...
metaphorically to refer to dawn, often mentioning its play of colors across the otherwise dark sky (''e.g.'', "rosy-fingered dawn").
The words "borealis" and "australis" are derived from the names of the ancient gods of the north wind (
Boreas) and the south wind (
Auster).
Occurrence
Most auroras occur in a band known as the "auroral zone",
which is typically 3° to 6° wide in latitude and between 10° and 20° from the
geomagnetic pole
The geomagnetic poles are antipodal points where the axis of a best-fitting dipole intersects the surface of Earth. This ''theoretical'' dipole is equivalent to a powerful bar magnet at the center of Earth, and comes closer than any other poin ...
s at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the "auroral oval", a band displaced by the solar wind towards the night side of Earth. Early evidence for a geomagnetic connection comes from the statistics of auroral observations.
Elias Loomis (1860),
and later Hermann Fritz (1881) and Sophus Tromholt (1881) in more detail, established that the aurora appeared mainly in the auroral zone.
In northern
latitude
In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north pol ...
s, the effect is known as the aurora borealis or the northern lights. The former term was coined by
Galileo
Galileo di Vincenzo Bonaiuti de' Galilei (15 February 1564 – 8 January 1642) was an Italian astronomer, physicist and engineer, sometimes described as a polymath. Commonly referred to as Galileo, his name was pronounced (, ). He was ...
in 1619, from the
Roman
Roman or Romans most often refers to:
*Rome, the capital city of Italy
*Ancient Rome, Roman civilization from 8th century BC to 5th century AD
*Roman people, the people of ancient Rome
*''Epistle to the Romans'', shortened to ''Romans'', a letter ...
goddess of the dawn and the
Greek name for the north wind. 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. The aurora australis is visible from high southern latitudes in
Antarctica
Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest contine ...
,
Chile
Chile, officially the Republic of Chile, is a country in the western part of South America. It is the southernmost country in the world, and the closest to Antarctica, occupying a long and narrow strip of land between the Andes to the east a ...
,
Argentina
Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
,
South Africa
South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring countri ...
,
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
and
Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
. The aurora borealis is visible from being close to the center of the Arctic Circle such as
Alaska
Alaska ( ; russian: Аляска, Alyaska; ale, Alax̂sxax̂; ; ems, Alas'kaaq; Yup'ik: ''Alaskaq''; tli, Anáaski) is a state located in the Western United States on the northwest extremity of North America. A semi-exclave of the U.S., ...
, the
Canadian Territories,
Iceland
Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
,
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...
,
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
,
Sweden
Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic country located on ...
,
Finland
Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...
and
Russia
Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...
. On rare occasions the aurora borealis can be seen further south, for example in
Estonia
Estonia, formally the Republic of Estonia, is a country by the Baltic Sea in Northern Europe. It is bordered to the north by the Gulf of Finland across from Finland, to the west by the sea across from Sweden, to the south by Latvia, a ...
,
Latvia
Latvia ( or ; lv, Latvija ; ltg, Latveja; liv, Leţmō), officially the Republic of Latvia ( lv, Latvijas Republika, links=no, ltg, Latvejas Republika, links=no, liv, Leţmō Vabāmō, links=no), is a country in the Baltic region of ...
,
Lithuania
Lithuania (; lt, Lietuva ), officially the Republic of Lithuania ( lt, Lietuvos Respublika, links=no ), is a country in the Baltic region of Europe. It is one of three Baltic states and lies on the eastern shore of the Baltic Sea. Lithuania ...
,
Scotland
Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...
,
Ireland
Ireland ( ; ga, Éire ; Ulster Scots dialect, Ulster-Scots: ) is an island in the Atlantic Ocean, North Atlantic Ocean, in Northwestern Europe, north-western Europe. It is separated from Great Britain to its east by the North Channel (Grea ...
,
Denmark
)
, song = ( en, "King Christian stood by the lofty mast")
, song_type = National and royal anthem
, image_map = EU-Denmark.svg
, map_caption =
, subdivision_type = Sovereign state
, subdivision_name = Danish Realm, Kingdom of Denmark
...
, and the northern part of the contiguous
United States
The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
.
A
geomagnetic storm causes the auroral ovals (north and south) to expand, bringing the aurora to lower latitudes. The instantaneous distribution of auroras ("auroral oval")
is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the
magnetic pole
Magnetic pole may refer to:
* One of the two ends of a magnet
* Magnetic monopole, a hypothetical elementary particle
* The magnetic poles of astronomical bodies, a special case of magnets, especially:
** The North Magnetic Pole
The north mag ...
in question is in between the observer and the
Sun. The aurora can be seen best at this time, which is called
magnetic midnight
Within the field of astronomy, Magnetic midnight is the time of day when the North or South Magnetic Pole is exactly in between the sun and an observer on earth's surface. This is the best time for observing auroras.
Because Earth's magnetic pol ...
.
Auroras seen within the auroral oval may be directly overhead, but 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, which can be subvisual.
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
The solar cycle, also known as the solar magnetic activity cycle, sunspot cycle, or Schwabe cycle, is a nearly periodic 11-year change in the Sun's activity measured in terms of variations in the number of observed sunspots on the Sun's surfac ...
or during the three years after the peak. 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", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) observed around the two polar cusps, the field lines separating the ones that close through Earth from those that are swept into the tail and close remotely.
Images
Early work on the imaging of the auroras was done in 1949 by the
University of Saskatchewan
A university () is an institution of higher (or tertiary) education and research which awards academic degrees in several academic disciplines. Universities typically offer both undergraduate and postgraduate programs. In the United States, t ...
using the
SCR-270 radar. The altitudes where auroral emissions occur were revealed by
Carl Størmer and his colleagues, who used cameras to triangulate more than 12,000 auroras. They discovered that most of the light is produced between 90 km (56 mi) and 150 km (93 mi) above the ground, while extending at times to more than 1000 km (620 mi).
Forms
According to Clark (2007), there are four main forms that can be seen from the ground, from least to most visible:
![Aurora shapes](https://upload.wikimedia.org/wikipedia/commons/2/29/Aurora_shapes.jpg)
* A mild ''glow'', near the horizon. These can be close to the limit of visibility, but can be distinguished from moonlit clouds because stars can be seen undiminished through the glow.
* ''Patches'' or ''surfaces'' that look like clouds.
* ''Arcs'' curve across the
sky
The sky is an unobstructed view upward from the surface of the Earth. It includes the atmosphere and outer space. It may also be considered a place between the ground and outer space, thus distinct from outer space.
In the field of astronomy, ...
.
* ''Rays'' are light and dark stripes across arcs, reaching upwards by various amounts.
* ''Coronas'' cover much of the sky and diverge from one point on it.
Brekke (1994) also described some auroras as ''curtains''.
The similarity to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are also known as ''discrete auroras'', which are at times bright enough to read a newspaper by at night.
These forms are consistent with auroras being shaped by Earth's magnetic field. The appearances of arcs, rays, curtains, and coronas are determined by the
shapes of the luminous parts of the atmosphere and a viewer's position.
Colors and wavelengths of auroral light
* Red: At its highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.
* Green: At lower altitudes, the more frequent collisions suppress the 630 nm (red) mode: rather the 557.7 nm emission (green) dominates. A fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to the high stability of the N
2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to
forbidden transition
In spectroscopy, a forbidden mechanism (forbidden transition or forbidden line) is a spectral line associated with absorption or emission of photons by atomic nuclei, atoms, or molecules which undergo a transition that is not allowed by a particul ...
s of atomic oxygen, a slow mechanism responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.
* Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.
* Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars,
Jupiter and Saturn.
* Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.
* Yellow and pink are
a mix of red and green or blue. Other shades of red, as well as orange, may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are linearly independent colors, additive synthesis could, in theory, produce most human-perceived colors, but the ones mentioned in this article comprise a virtually exhaustive list.
Changes with time
![Keogram explainer](https://upload.wikimedia.org/wikipedia/commons/d/d0/Keogram_explainer.gif)
Auroras change with time. Over the night, they begin with glows and progress towards coronas, although they may not reach them. They tend to fade in the opposite order.
Until about 1963 it was thought that these changes are due to the rotation of the Earth under a pattern fixed with respect to the Sun. Later it was found by comparing all-sky films of auroras from different places (collected during the
International Geophysical Year
The International Geophysical Year (IGY; french: Année géophysique internationale) was an international scientific project that lasted from 1 July 1957 to 31 December 1958. It marked the end of a long period during the Cold War when scientific ...
) that they often undergo global changes in a process called
auroral substorm
A substorm, sometimes referred to as a magnetospheric substorm or an auroral substorm, is a brief disturbance in the Earth's magnetosphere that causes energy to be released from the "tail" of the magnetosphere and injected into the high latitude ...
. They change in a few minutes from quiet arcs all along the auroral oval to active displays along the darkside and after 1 – 3 hours they gradually change back. Changes in auroras over time are commonly visualized using
keogram
A keogram ("keo" from "Keoeeit" – Inuit word for "Aurora Borealis") is a way of displaying the intensity of an auroral display, taken from a narrow part of a round screen recorded by a camera, more specifically and ideally in practice a " whole ...
s.
At shorter time scales, auroras can change their appearances and intensity, sometimes so slowly as to be difficult to notice, and at other times rapidly down to the sub-second scale.
The phenomenon of pulsating auroras is an example of intensity variations over short timescales, typically with periods of 2–20 seconds. This type of aurora is generally accompanied by decreasing peak emission heights of about 8 km for blue and green emissions and above average solar wind speeds (~ 500 km/s).
Other auroral radiation
In addition, the aurora and associated currents produce a strong radio emission around 150 kHz known as
auroral kilometric radiation
Auroral kilometric radiation (AKR) is the intense radio radiation emitted in the acceleration zone (at a height of three times the radius of the Earth) of the polar lights. The radiation mainly comes from cyclotron radiation from electrons orbiti ...
(AKR), discovered in 1972. Ionospheric absorption makes AKR only observable from space. X-ray emissions, originating from the particles associated with auroras, have also been detected.
Noise
Aurora
noise
Noise is unwanted sound considered unpleasant, loud or disruptive to hearing. From a physics standpoint, there is no distinction between noise and desired sound, as both are vibrations through a medium, such as air or water. The difference arise ...
, similar to a crackling noise, begins about above Earth's surface and is caused by charged particles in an
inversion
Inversion or inversions may refer to:
Arts
* , a French gay magazine (1924/1925)
* ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas
* Inversion (music), a term with various meanings in music theory and musical set theory
* ...
layer of the atmosphere formed during a cold night. The charged particles discharge when particles from the Sun hit the inversion layer, creating the noise.
Unusual types
STEVE
In 2016, more than fifty
citizen science
Citizen science (CS) (similar to community science, crowd science, crowd-sourced science, civic science, participatory monitoring, or volunteer monitoring) is scientific research conducted with participation from the public (who are sometimes re ...
observations described what was to them an unknown type of aurora which they named "
STEVE
''yes'Steve is a masculine given name, usually a short form (hypocorism) of Steven or Stephen
Notable people with the name include:
steve jops
* Steve Abbott (disambiguation), several people
* Steve Adams (disambiguation), several people
* Steve ...
", for "Strong Thermal Emission Velocity Enhancement". STEVE is not an aurora but is caused by a wide ribbon of hot
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
at an altitude of , with a temperature of and flowing at a speed of (compared to outside the ribbon).
Picket-fence aurora
The processes that cause STEVE also are associated with a picket-fence aurora, although the latter can be seen without STEVE.
It is an aurora because it is caused by precipitation of electrons in the atmosphere but it appears outside the auroral oval, closer to the
equator
The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...
than typical auroras. When the picket-fence aurora appears with STEVE, it is below.
Dune aurora
First reported in 2020 and confirmed in 2021
the dune aurora phenomenon was discovered by Finnish
citizen scientists
Citizen science (CS) (similar to community science, crowd science, crowd-sourced science, civic science, participatory monitoring, or volunteer monitoring) is scientific research conducted with participation from the public (who are sometimes re ...
. It consists of regularly-spaced, parallel stripes of brighter emission in the green diffuse aurora which give the impression of sand dunes. The phenomenon is believed to be caused by the modulation of atomic oxygen density by a large-scale atmospheric wave travelling horizontally in a waveguide through an
inversion
Inversion or inversions may refer to:
Arts
* , a French gay magazine (1924/1925)
* ''Inversion'' (artwork), a 2005 temporary sculpture in Houston, Texas
* Inversion (music), a term with various meanings in music theory and musical set theory
* ...
layer in the
mesosphere
The mesosphere (; ) is the third layer of the atmosphere, directly above the stratosphere and directly below the thermosphere. In the mesosphere, temperature decreases as altitude increases. This characteristic is used to define its limits: it ...
in presence of
electron precipitation.
Horse-collar aurora
Horse-collar aurora (HCA) are auroral features in which the auroral ellipse shifts poleward during the dawn and dusk portions and the polar cap becomes teardrop-shaped. They form during periods when the interplanetary magnetic field (IMF) is permanently northward, when the IMF clock angle is small. Their formation is associated with the closure of the magnetic flux at the top of the dayside magnetosphere by the double lobe reconnection (DLR). There are approximately 8 HCA events per month, with no seasonal dependence, and that the IMF must be within 30 degrees of northwards.
Causes
A full understanding of the physical processes which lead to different types of auroras is still incomplete, but the basic cause involves the interaction of the
solar wind with
Earth's magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dyn ...
. The varying intensity of the solar wind produces effects of different magnitudes but includes one or more of the following physical scenarios.
# A quiescent solar wind flowing past Earth's magnetosphere steadily interacts with it and can both inject solar wind particles directly onto the geomagnetic field lines that are 'open', as opposed to being 'closed' in the opposite hemisphere, and provide diffusion through the
bow shock. It can also cause particles already trapped in the
radiation belts to precipitate into the atmosphere. Once particles are lost to the atmosphere from the radiation belts, under quiet conditions, new ones replace them only slowly, and the loss-cone becomes depleted. In the magnetotail, however, particle trajectories seem constantly to reshuffle, probably when the particles cross the very weak magnetic field near the equator. As a result, the flow of electrons in that region is nearly the same in all directions ("isotropic") and assures a steady supply of leaking electrons. The leakage of electrons does not leave the tail positively charged, because each leaked electron lost to the atmosphere is replaced by a low energy electron drawn upward from the
ionosphere
The ionosphere () is the ionized part of the upper atmosphere of Earth, from about to above sea level, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an ...
. Such replacement of "hot" electrons by "cold" ones is in complete accord with the
second law of thermodynamics
The second law of thermodynamics is a physical law based on universal experience concerning heat and Energy transformation, energy interconversions. One simple statement of the law is that heat always moves from hotter objects to colder objects ( ...
. The complete process, which also generates an electric ring current around Earth, is uncertain.
# Geomagnetic disturbance from an enhanced
solar wind causes distortions of the
magnetotail ("magnetic substorms"). These 'substorms' tend to occur after prolonged spells (on the order of hours) during which the interplanetary magnetic field has had an appreciable southward component. This leads to a higher rate of interconnection between its field lines and those of Earth. As a result, the solar wind moves
magnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
(tubes of magnetic field lines, 'locked' together with their resident plasma) from the day side of Earth to the magnetotail, widening the obstacle it presents to the solar wind flow and constricting the tail on the night-side. Ultimately some tail plasma can separate ("
magnetic reconnection"); some blobs ("
plasmoid
A plasmoid is a coherent structure of plasma and magnetic fields. Plasmoids have been proposed to explain natural phenomena such as ball lightning, magnetic bubbles in the magnetosphere, and objects in cometary tails, in the solar wind, in th ...
s") are squeezed downstream and are carried away with the solar wind; others are squeezed toward Earth where their motion feeds strong outbursts of auroras, mainly around midnight ("unloading process"). A geomagnetic storm resulting from greater interaction adds many more particles to the plasma trapped around Earth, also producing enhancement of the "ring current". Occasionally the resulting modification of Earth's magnetic field can be so strong that it produces auroras visible at middle latitudes, on field lines much closer to the equator than those of the auroral zone.
#:
![Moon and Aurora](https://upload.wikimedia.org/wikipedia/commons/4/4c/Moon_and_Aurora.jpg)
# Acceleration of auroral charged particles invariably accompanies a magnetospheric disturbance that causes an aurora. This mechanism, which is believed to predominantly arise from strong electric fields along the magnetic field or wave-particle interactions, raises the velocity of a particle in the direction of the guiding magnetic field. The pitch angle is thereby decreased and increases the chance of it being precipitated into the atmosphere. Both electromagnetic and electrostatic waves, produced at the time of greater geomagnetic disturbances, make a significant contribution to the energizing processes that sustain an aurora. Particle acceleration provides a complex intermediate process for transferring energy from the solar wind indirectly into the atmosphere.
![Aurora australis 20050911](https://upload.wikimedia.org/wikipedia/commons/9/9a/Aurora_australis_20050911.jpg)
The details of these phenomena are not fully understood. However, it is clear that the prime source of auroral particles is the solar wind feeding the magnetosphere, the reservoir containing the radiation zones and temporarily magnetically-trapped particles confined by the geomagnetic field, coupled with particle acceleration processes.
Auroral particles
The immediate cause of the ionization and excitation of atmospheric constituents leading to auroral emissions was discovered in 1960, when a pioneering rocket flight from Fort Churchill in Canada revealed a flux of electrons entering the atmosphere from above. Since then an extensive collection of measurements has been acquired painstakingly and with steadily improving resolution since the 1960s by many research teams using rockets and satellites to traverse the auroral zone. The main findings have been that auroral arcs and other bright forms are due to electrons that have been accelerated during the final few 10,000 km or so of their plunge into the atmosphere. These electrons often, but not always, exhibit a peak in their energy distribution, and are preferentially aligned along the local direction of the magnetic field.
Electrons mainly responsible for diffuse and pulsating auroras have, in contrast, a smoothly falling energy distribution, and an angular (pitch-angle) distribution favouring directions perpendicular to the local magnetic field. Pulsations were discovered to originate at or close to the equatorial crossing point of auroral zone magnetic field lines. Protons are also associated with auroras, both discrete and diffuse.
Atmosphere
Auroras result from emissions of
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they always ...
s in Earth's upper
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
, above , from
ionized nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
atoms regaining an electron, and
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
atoms and
nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
based molecules returning from an
excited state
In quantum mechanics, an excited state of a system (such as an atom, molecule or nucleus) is any quantum state of the system that has a higher energy than the ground state (that is, more energy than the absolute minimum). Excitation refers to a ...
to
ground state
The ground state of a quantum-mechanical system is its stationary state of lowest energy; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. ...
. They are ionized or excited by the collision of particles precipitated into the atmosphere. Both incoming electrons and protons may be involved. Excitation energy is lost within the atmosphere by the emission of a photon, or by collision with another atom or molecule:
;
Oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
emissions: green or orange-red, depending on the amount of energy absorbed.
;
Nitrogen
Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...
emissions:blue, purple or red; blue and purple if the molecule regains an electron after it has been ionized, red if returning to ground state from an excited state.
Oxygen is unusual in terms of its return to ground state: it can take 0.7 seconds to emit the 557.7 nm green light and up to two minutes for the red 630.0 nm emission. Collisions with other atoms or molecules absorb the excitation energy and prevent emission, this process is called
collisional quenching. Because the highest parts of the atmosphere contain a higher percentage of oxygen and lower particle densities, such collisions are rare enough to allow time for oxygen to emit red light. Collisions become more frequent progressing down into the atmosphere due to increasing density, so that red emissions do not have time to happen, and eventually, even green light emissions are prevented.
This is why there is a color differential with altitude; at high altitudes oxygen red dominates, then oxygen green and nitrogen blue/purple/red, then finally nitrogen blue/purple/red when collisions prevent oxygen from emitting anything. Green is the most common color. Then comes pink, a mixture of light green and red, followed by pure red, then yellow (a mixture of red and green), and finally, pure blue.
Precipitating protons generally produce optical emissions as incident
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic, an ...
atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.
Ionosphere
Bright auroras are generally associated with
Birkeland currents (Schield et al., 1969; Zmuda and Armstrong, 1973), which flow down into the ionosphere on one side of the pole and out on the other. In between, some of the current connects directly through the ionospheric E layer (125 km); the rest ("region 2") detours, leaving again through field lines closer to the equator and closing through the "partial ring current" carried by magnetically trapped plasma. The ionosphere is an
ohmic conductor, so some consider that such currents require a driving voltage, which an, as yet unspecified, dynamo mechanism can supply. Electric field probes in orbit above the polar cap suggest voltages of the order of 40,000 volts, rising up to more than 200,000 volts during intense magnetic storms. In another interpretation, the currents are the direct result of electron acceleration into the atmosphere by wave/particle interactions.
Ionospheric resistance has a complex nature, and leads to a secondary
Hall current
The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was disco ...
flow. By a strange twist of physics, the magnetic disturbance on the ground due to the main current almost cancels out, so most of the observed effect of auroras is due to a secondary current, the auroral
electrojet. An auroral electrojet index (measured in nanotesla) is regularly derived from ground data and serves as a general measure of auroral activity.
Kristian Birkeland[ out-of-print, full text online] deduced that the currents flowed in the east–west directions along the auroral arc, and such currents, flowing from the dayside toward (approximately) midnight were later named "auroral electrojets" (see also
Birkeland currents).
Interaction of the solar wind with Earth
Earth is constantly immersed in the
solar wind, a flow of magnetized hot plasma (a gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree temperature of the Sun's outermost layer, the
corona. The solar wind reaches Earth with a velocity typically around 400 km/s, a density of around 5 ions/cm
3 and a magnetic field intensity of around 2–5 nT (for comparison, Earth's surface field is typically 30,000–50,000 nT). During
magnetic storms, in particular, flows can be several times faster; the
interplanetary magnetic field (IMF) may also be much stronger.
Joan Feynman deduced in the 1970s that the long-term averages of solar wind speed correlated with geomagnetic activity. Her work resulted from data collected by the
Explorer 33
Explorer 33, also known as IMP-D and AIMP-1, was a spacecraft in the Explorer program launched by NASA on 1 July 1966 on a mission of scientific exploration. It was the fourth satellite launched as part of the Interplanetary Monitoring Platform ...
spacecraft.
The solar wind and magnetosphere consist of
plasma
Plasma or plasm may refer to:
Science
* Plasma (physics), one of the four fundamental states of matter
* Plasma (mineral), a green translucent silica mineral
* Quark–gluon plasma, a state of matter in quantum chromodynamics
Biology
* Blood pla ...
(ionized gas), which conducts electricity. It is well known (since
Michael Faraday
Michael Faraday (; 22 September 1791 – 25 August 1867) was an English scientist who contributed to the study of electromagnetism and electrochemistry. His main discoveries include the principles underlying electromagnetic inducti ...
's work around 1830) that when an electrical conductor is placed within a magnetic field while relative motion occurs in a direction that the conductor cuts ''across'' (or is cut ''by''), rather than ''along'', the lines of the magnetic field, an electric current is induced within the conductor. The strength of the current depends on a) the rate of relative motion, b) the strength of the magnetic field, c) the number of conductors ganged together and d) the distance between the conductor and the magnetic field, while the ''direction'' of flow is dependent upon the direction of relative motion.
Dynamos make use of this basic process ("the
dynamo effect"), any and all conductors, solid or otherwise are so affected, including plasmas and other fluids.
The IMF originates on the Sun, linked to the
sunspot
Sunspots are phenomena on the Sun's photosphere that appear as temporary spots that are darker than the surrounding areas. They are regions of reduced surface temperature caused by concentrations of magnetic flux that inhibit convection. Sun ...
s, and its
field lines (lines of force) are dragged out by the solar wind. That alone would tend to line them up in the Sun-Earth direction, but the rotation of the Sun angles them at Earth by about 45 degrees forming a spiral in the ecliptic plane, known as the
Parker spiral. The field lines passing Earth are therefore usually linked to those near the western edge ("limb") of the visible Sun at any time.
The solar wind and the magnetosphere, being two electrically conducting fluids in relative motion, should be able in principle to generate electric currents by dynamo action and impart energy from the flow of the solar wind. However, this process is hampered by the fact that plasmas conduct readily along magnetic field lines, but less readily perpendicular to them. Energy is more effectively transferred by the temporary magnetic connection between the field lines of the solar wind and those of the magnetosphere. Unsurprisingly this process is known as
magnetic reconnection. As already mentioned, it happens most readily when the interplanetary field is directed southward, in a similar direction to the geomagnetic field in the inner regions of both the
north magnetic pole and
south magnetic pole.
Auroras are more frequent and brighter during the intense phase of the solar cycle when
coronal mass ejections
A coronal mass ejection (CME) is a significant release of plasma (physics), plasma and accompanying magnetic field from the Sun's Solar corona, corona into the heliosphere. CMEs are often associated with solar flares and other forms of solar ac ...
increase the intensity of the solar wind.
Magnetosphere
![Structure_of_the_magnetosphere_LanguageSwitch](https://upload.wikimedia.org/wikipedia/commons/b/bb/Structure_of_the_magnetosphere_LanguageSwitch.svg)
Earth's
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
is shaped by the impact of the solar wind on Earth's magnetic field. This forms an obstacle to the flow, diverting it, at an average distance of about 70,000 km (11 Earth radii or Re), producing a
bow shock 12,000 km to 15,000 km (1.9 to 2.4 Re) further upstream. The width of the magnetosphere abreast of Earth is typically 190,000 km (30 Re), and on the night side a long "magnetotail" of stretched field lines extends to great distances (> 200 Re).
The high latitude magnetosphere is filled with plasma as the solar wind passes Earth. The flow of plasma into the magnetosphere increases with additional turbulence, density, and speed in the solar wind. This flow is favored by a southward component of the IMF, which can then directly connect to the high latitude geomagnetic field lines. The flow pattern of magnetospheric plasma is mainly from the magnetotail toward Earth, around Earth and back into the solar wind through the
magnetopause on the day-side. In addition to moving perpendicular to Earth's magnetic field, some magnetospheric plasma travels down along Earth's magnetic field lines, gains additional energy and loses it to the atmosphere in the auroral zones. The cusps of the magnetosphere, separating geomagnetic field lines that close through Earth from those that close remotely allow a small amount of solar wind to directly reach the top of the atmosphere, producing an auroral glow.
On 26 February 2008,
THEMIS probes were able to determine, for the first time, the triggering event for the onset of
magnetospheric substorm
A substorm, sometimes referred to as a magnetospheric substorm or an auroral substorm, is a brief disturbance in the Earth's magnetosphere that causes energy to be released from the "tail" of the magnetosphere and injected into the high latitude ...
s. Two of the five probes, positioned approximately one third the distance to the Moon, measured events suggesting a
magnetic reconnection event 96 seconds prior to auroral intensification.
Geomagnetic storms that ignite auroras may occur more often during the months around the
equinoxes. It is not well understood, but geomagnetic storms may vary with Earth's seasons. Two factors to consider are the tilt of both the solar and Earth's axis to the ecliptic plane. As Earth orbits throughout a year, it experiences an interplanetary magnetic field (IMF) from different latitudes of the Sun, which is tilted at 8 degrees. Similarly, the 23-degree tilt of Earth's axis about which the geomagnetic pole rotates with a diurnal variation changes the daily average angle that the geomagnetic field presents to the incident IMF throughout a year. These factors combined can lead to minor cyclical changes in the detailed way that the IMF links to the magnetosphere. In turn, this affects the average probability of opening a door through which energy from the solar wind can reach Earth's inner magnetosphere and thereby enhance auroras. Recent evidence in 2021 has shown that individual separate substorms may in fact be correlated networked communities.
Auroral particle acceleration
Just as there are many types of aurora, there are many different mechanisms that accelerate auroral particles into the atmosphere. Electron aurora in Earth's auroral zone (i.e. commonly visible aurora) can be split into two main categories with different immediate causes: diffuse and discrete aurora. Diffuse aurora appear relatively structureless to an observer on the ground, with indistinct edges and amorphous forms. Discrete aurora are structured into distinct features with well-defined edges such as arcs, rays and coronas; they also tend to be much brighter than the diffuse aurora.
In both cases, the electrons that eventually cause the aurora start out as electrons trapped by the magnetic field in Earth's
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
. These
trapped particles
Trapped may refer to:
Films
* ''Trapped'' (1931 film), a crime drama short starring Lina Basquette
* ''Trapped'' (1937 film), an American western starring Charles Starrett
* ''Trapped'' (1949 film), a semidocumentary film noir directed by Richar ...
bounce back and forth along
magnetic field lines and are prevented from hitting the atmosphere by the
magnetic mirror formed by the increasing magnetic field strength closer to Earth. The magnetic mirror's ability to trap a particle depends on the particle's
pitch angle: the angle between its direction of motion and the local magnetic field. An aurora is created by processes that decrease the pitch angle of many individual electrons, freeing them from the magnetic trap and causing them to hit the atmosphere.
In the case of diffuse auroras, the electron pitch angles are altered by their interaction with various
plasma waves In plasma physics, waves in plasmas are an interconnected set of particles and fields which propagate in a periodically repeating fashion. A plasma is a quasineutral, electrically conductive fluid. In the simplest case, it is composed of electron ...
. Each interaction is essentially wave-particle
scattering
Scattering is a term used in physics to describe a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including ...
; the electron energy after interacting with the wave is similar to its energy before interaction, but the direction of motion is altered. If the final direction of motion after scattering is close to the field line (specifically, if it falls within the
loss cone) then the electron will hit the atmosphere. Diffuse auroras are caused by the collective effect of many such scattered electrons hitting the atmosphere. The process is mediated by the plasma waves, which become stronger during periods of high
geomagnetic activity
Earth's magnetic field, also known as the geomagnetic field, is the magnetic field that extends from Earth's interior out into space, where it interacts with the solar wind, a stream of charged particles emanating from the Sun. The magnetic fi ...
, leading to increased diffuse aurora at those times.
In the case of discrete auroras, the trapped electrons are accelerated toward Earth by electric fields that form at an altitude of about 4000–12000 km in the "auroral acceleration region". The electric fields point away from Earth (i.e. upward) along the magnetic field line.
[The theory of acceleration by parallel electric fields is reviewed in detail by ] Electrons moving downward through these fields gain a substantial amount of energy (on the order of a few
keV) in the direction along the magnetic field line toward Earth. This field-aligned acceleration decreases the pitch angle for all of the electrons passing through the region, causing many of them to hit the upper atmosphere. In contrast to the scattering process leading to diffuse auroras, the electric field increases the kinetic energy of all of the electrons transiting downward through the acceleration region by the same amount. This accelerates electrons starting from the magnetosphere with initially low energies (10s of eV or less) to energies required to create an aurora (100s of eV or greater), allowing that large source of particles to contribute to creating auroral light.
The accelerated electrons carry an electric current along the magnetic field lines (a
Birkeland current). Since the electric field points in the same direction as the current, there is a net conversion of electromagnetic energy into particle energy in the auroral acceleration region (an
electric load). The energy to power this load is eventually supplied by the magnetized solar wind flowing around the obstacle of Earth's magnetic field, although exactly how that power flows through the magnetosphere is still an active area of research.
[A discussion of 8 theories in use in 2020 as well as several no longer in common use can be found in: ] While the energy to power the aurora is ultimately derived from the solar wind, the electrons themselves do not travel directly from the solar wind into Earth's auroral zone; magnetic field lines from these regions do not connect to the solar wind, so there is no direct access for solar wind electrons.
Some auroral features are also created by electrons accelerated by
Alfvén waves. At small wavelengths (comparable to the
electron inertial length or
ion gyroradius), Alfvén waves develop a significant electric field parallel to the background magnetic field; this can accelerate electrons due to a process of
Landau damping. If the electrons have a speed close to that of the wave's phase velocity, they are accelerated in a manner analogous to a surfer catching an ocean wave. This constantly-changing wave electric field can accelerate electrons along the field line, causing some of them to hit the atmosphere. Electrons accelerated by this mechanism tend to have a broad energy spectrum, in contrast to the sharply-peaked energy spectrum typical of electrons accelerated by quasi-static electric fields.
In addition to the discrete and diffuse electron aurora, proton aurora is caused when magnetospheric protons collide with the upper atmosphere. The proton gains an electron in the interaction, and the resulting neutral hydrogen atom emits photons. The resulting light is too dim to be seen with the naked eye. Other aurora not covered by the above discussion include transpolar arcs (formed poleward of the auroral zone), cusp aurora (formed in two small high-latitude areas on the dayside) and some non-terrestrial auroras.
Historically significant events
The discovery of a 1770 Japanese
diary in 2017 depicting auroras above the ancient Japanese capital of
Kyoto
Kyoto (; Japanese: , ''Kyōto'' ), officially , is the capital city of Kyoto Prefecture in Japan. Located in the Kansai region on the island of Honshu, Kyoto forms a part of the Keihanshin metropolitan area along with Osaka and Kobe. , the ci ...
suggested that the storm may have been 7% larger than the
Carrington event
The Carrington Event was the most intense geomagnetic storm in recorded history, peaking from 1 to 2 September 1859 during solar cycle 10. It created strong auroral displays that were reported globally and caused sparking and even fires in mult ...
, which affected telegraph networks.
The auroras that resulted from the "
great geomagnetic storm" on both 28 August and 2 September 1859, however, are thought to be the most spectacular in recent recorded history. In a paper to the
Royal Society
The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
on 21 November 1861, Balfour Stewart described both auroral events as documented by a self-recording
magnetograph
Magnetograph may refer to:
* Solar magnetograph, an instrument that produces solar magnetogram
In solar observation, a magnetogram is a pictorial representation of the spatial variations in strength of the solar magnetic field.
Solar magnetogram ...
at the
Kew Observatory and established the connection between the 2 September 1859 auroral storm and the
Carrington–Hodgson flare event when he observed that "It is not impossible to suppose that in this case our luminary was taken ''in the act''." The second auroral event, which occurred on 2 September 1859, was a result of the (unseen) coronal mass ejection associated with the exceptionally intense Carrington–Hodgson white light
solar flare on 1 September 1859. This event produced auroras so widespread and extraordinarily bright that they were seen and reported in published scientific measurements, ship logs, and newspapers throughout the United States, Europe, Japan, and Australia. It was reported by ''
The New York Times
''The New York Times'' (''the Times'', ''NYT'', or the Gray Lady) is a daily newspaper based in New York City with a worldwide readership reported in 2020 to comprise a declining 840,000 paid print subscribers, and a growing 6 million paid ...
'' that in
Boston
Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
on Friday 2 September 1859 the aurora was "so brilliant that at about one o'clock ordinary print could be read by the light".
One o'clock EST time on Friday 2 September would have been 6:00 GMT; the self-recording magnetograph at the
Kew Observatory was recording the
geomagnetic storm, which was then one hour old, at its full intensity. Between 1859 and 1862,
Elias Loomis published a series of nine papers on the
Great Auroral Exhibition of 1859 in the ''
American Journal of Science
The ''American Journal of Science'' (''AJS'') is the United States of America's longest-running scientific journal, having been published continuously since its conception in 1818 by Professor Benjamin Silliman, who edited and financed it himself ...
'' where he collected worldwide reports of the auroral event.
[See:
*
*
*
*
*
*
*
*
* ]
That aurora is thought to have been produced by one of the most intense
coronal mass ejections in history. It is also notable for the fact that it is the first time where the phenomena of auroral activity and electricity were unambiguously linked. This insight was made possible not only due to scientific
magnetometer
A magnetometer is a device that measures magnetic field or magnetic dipole moment. Different types of magnetometers measure the direction, strength, or relative change of a magnetic field at a particular location. A compass is one such device, o ...
measurements of the era, but also as a result of a significant portion of the of
telegraph
Telegraphy is the long-distance transmission of messages where the sender uses symbolic codes, known to the recipient, rather than a physical exchange of an object bearing the message. Thus flag semaphore is a method of telegraphy, whereas p ...
lines then in service being significantly disrupted for many hours throughout the storm. Some telegraph lines, however, seem to have been of the appropriate length and orientation to produce a sufficient
geomagnetically induced current from the
electromagnetic field
An electromagnetic field (also EM field or EMF) is a classical (i.e. non-quantum) field produced by (stationary or moving) electric charges. It is the field described by classical electrodynamics (a classical field theory) and is the classical c ...
to allow for continued communication with the telegraph operator power supplies switched off. The following conversation occurred between two operators of the American Telegraph Line between
Boston
Boston (), officially the City of Boston, is the state capital and most populous city of the Commonwealth of Massachusetts, as well as the cultural and financial center of the New England region of the United States. It is the 24th- mo ...
and
Portland, Maine, on the night of 2 September 1859 and reported in the ''Boston Traveler'':
The conversation was carried on for around two hours using no
battery
Battery most often refers to:
* Electric battery, a device that provides electrical power
* Battery (crime), a crime involving unlawful physical contact
Battery may also refer to:
Energy source
*Automotive battery, a device to provide power t ...
power at all and working solely with the current induced by the aurora, and it was said that this was the first time on record that more than a word or two was transmitted in such manner.
Such events led to the general conclusion that
Historical views and folklore
The earliest datable record of an aurora was recorded in the ''
Bamboo Annals
The ''Bamboo Annals'' (), also known as the ''Ji Tomb Annals'' (), is a chronicle of ancient China.
It begins in the earliest legendary time (the age of the Yellow Emperor) and extends to 299 BC, with the later centuries focusing on the history ...
'', a historical chronicle of the history of ancient China, on 977 or 957 BCE.
An aurora was described by the
Greek explorer Pytheas
Pytheas of Massalia (; Ancient Greek: Πυθέας ὁ Μασσαλιώτης ''Pythéas ho Massaliōtēs''; Latin: ''Pytheas Massiliensis''; born 350 BC, 320–306 BC) was a Greeks, Greek List of Graeco-Roman geographers, geographer, explor ...
in the 4th century BC.
Seneca
Seneca may refer to:
People and language
* Seneca (name), a list of people with either the given name or surname
* Seneca people, one of the six Iroquois tribes of North America
** Seneca language, the language of the Seneca people
Places Extrat ...
wrote about auroras in the first book of his ''
Naturales Quaestiones'', classifying them, for instance as ''pithaei'' ('barrel-like'); ''chasmata'' ('chasm'); ''pogoniae'' ('bearded'); ''cyparissae'' ('like
cypress
Cypress is a common name for various coniferous trees or shrubs of northern temperate regions that belong to the family Cupressaceae. The word ''cypress'' is derived from Old French ''cipres'', which was imported from Latin ''cypressus'', the ...
trees'), and describing their manifold colors. He wrote about whether they were above or below the
clouds
In meteorology, a cloud is an aerosol consisting of a visible mass of miniature liquid droplets, frozen crystals, or other particles suspended in the atmosphere of a planetary body or similar space. Water or various other chemicals may com ...
, and recalled that under
Tiberius
Tiberius Julius Caesar Augustus (; 16 November 42 BC – 16 March AD 37) was the second Roman emperor. He reigned from AD 14 until 37, succeeding his stepfather, the first Roman emperor Augustus. Tiberius was born in Rome in 42 BC. His father ...
, an aurora formed above the port city of
Ostia
Ostia may refer to:
Places
*Ostia (Rome), a municipio (also called ''Ostia Lido'' or ''Lido di Ostia'') of Rome
*Ostia Antica, a township and port of ancient Rome
*Ostia Antica (district), a district of the commune of Rome
Arts and entertainment ...
that was so intense and red that a cohort of the army, stationed nearby for fire duty, galloped to the rescue. It has been suggested that
Pliny the Elder
Gaius Plinius Secundus (AD 23/2479), called Pliny the Elder (), was a Roman author, naturalist and natural philosopher, and naval and army commander of the early Roman Empire, and a friend of the emperor Vespasian. He wrote the encyclopedic '' ...
depicted the aurora borealis in his ''
Natural History'', when he refers to ''trabes'', ''chasma'', 'falling red flames' and 'daylight in the night'.
The earliest depiction of the aurora may have been a
Cro-Magnon
Early European modern humans (EEMH), or Cro-Magnons, were the first early modern humans (''Homo sapiens'') to settle in Europe, migrating from Western Asia, continuously occupying the continent possibly from as early as 56,800 years ago. They ...
cave painting
In archaeology, Cave paintings are a type of parietal art (which category also includes petroglyphs, or engravings), found on the wall or ceilings of caves. The term usually implies prehistoric origin, and the oldest known are more than 40,000 ye ...
dated to 30,000 BC.
The oldest known written record of the aurora was in a Chinese legend written around 2600 BC. On an autumn around 2000 BC,
according to a legend, a young woman named Fubao was sitting alone in the wilderness by a bay, when suddenly a "magical band of light" appeared like "moving clouds and flowing water", turning into a bright
halo around the
Big Dipper, which cascaded a pale silver brilliance, illuminating the earth and making shapes and shadows seem alive. Moved by this sight, Fubao became pregnant and gave birth to a son, the Emperor
Xuanyuan
The Yellow Emperor, also known as the Yellow Thearch or by his Chinese name Huangdi (), is a deity ('' shen'') in Chinese religion, one of the legendary Chinese sovereigns and culture heroes included among the mytho-historical Three Sovereign ...
, known legendarily as the initiator of
Chinese culture
Chinese culture () is one of the world's oldest cultures, originating thousands of years ago. The culture prevails across a large geographical region in East Asia and is extremely diverse and varying, with customs and traditions varying grea ...
and the ancestor of all Chinese people. In the ''
Shanhaijing'', a creature named 'Shilong' is described to be like a red dragon shining in the night sky with a body a thousand miles long. In ancient times, the Chinese did not have a fixed word for the aurora, so it was named according to the different shapes of the aurora, such as "Sky Dog ("天狗")", "Sword/Knife Star ("刀星")", "Chiyou banner ("蚩尤旗")", "Sky's Open Eyes ("天开眼")", and "Stars like Rain ("星陨如雨")".
In
Japanese folklore,
pheasants were considered messengers from heaven. However, researchers from Japan's Graduate University for Advanced Studies and National Institute of Polar Research claimed in March 2020 that red pheasant tails witnessed across the night sky over Japan in 620 A.D., might be a red aurora produced during a magnetic storm.
![Aurora australis](https://upload.wikimedia.org/wikipedia/commons/7/7f/Aurora_australis.jpg)
In the traditions of
Aboriginal Australians
Aboriginal Australians are the various Indigenous peoples of the Australian mainland and many of its islands, such as Tasmania, Fraser Island, Hinchinbrook Island, the Tiwi Islands, and Groote Eylandt, but excluding the Torres Strait Islands ...
, the Aurora Australis is commonly associated with fire. For example, the
Gunditjmara people
The Gunditjmara or Gunditjamara, also known as Dhauwurd Wurrung, are an Aboriginal Australian people of southwestern Victoria (Australia), Victoria. They are the traditional owners of the areas now encompassing Warrnambool, Port Fairy, Woolsthorp ...
of western
Victoria called auroras ''puae buae'' ('ashes'), while the
Gunai people of eastern Victoria perceived auroras as
bushfires in the spirit world. The
Dieri
The Diyari (), alternatively transcribed as Dieri (), is an Indigenous Australian group of the South Australian desert originating in and around the delta of Cooper Creek to the east of Lake Eyre.
Language
Diyari is classified as one of the Ka ...
people of
South Australia
South Australia (commonly abbreviated as SA) is a state in the southern central part of Australia. It covers some of the most arid parts of the country. With a total land area of , it is the fourth-largest of Australia's states and territories ...
say that an auroral display is ''kootchee'', an evil spirit creating a large fire. Similarly, the
Ngarrindjeri people
The Ngarrindjeri people are the traditional Aboriginal Australian people of the lower Murray River, eastern Fleurieu Peninsula, and the Coorong of the southern-central area of the state of South Australia. The term ''Ngarrindjeri'' means "belo ...
of South Australia refer to auroras seen over
Kangaroo Island as the campfires of spirits in the 'Land of the Dead'. Aboriginal people in southwest
Queensland
)
, nickname = Sunshine State
, image_map = Queensland in Australia.svg
, map_caption = Location of Queensland in Australia
, subdivision_type = Country
, subdivision_name = Australia
, established_title = Before federation
, established_ ...
believe the auroras to be the fires of the ''Oola Pikka'', ghostly spirits who spoke to the people through auroras. Sacred law forbade anyone except male elders from watching or interpreting the messages of ancestors they believed were transmitted through an aurora.
Among the
Māori people
The Māori (, ) are the indigenous Polynesian people of mainland New Zealand (). Māori originated with settlers from East Polynesia, who arrived in New Zealand in several waves of canoe voyages between roughly 1320 and 1350. Over several ce ...
of
New Zealand
New Zealand ( mi, Aotearoa ) is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and over 700 smaller islands. It is the sixth-largest island count ...
, aurora australis or ''Tahunui-a-rangi'' ("great torches in the sky") were alight by ancestors who sailed south to a "land of ice" (or their descendants);
said people were said to be
Ui-te-Rangiora's expedition party who had reached the Antarctic
Southern Ocean
The Southern Ocean, also known as the Antarctic Ocean, comprises the southernmost waters of the World Ocean, generally taken to be south of 60° S latitude and encircling Antarctica. With a size of , it is regarded as the second-small ...
around the 7th century.
![Utsjoki](https://upload.wikimedia.org/wikipedia/commons/e/e6/Utsjoki.vaakuna.svg)
In Scandinavia, the first mention of ''norðrljós'' (the northern lights) is found in the Norwegian chronicle ''
Konungs Skuggsjá
''Konungs skuggsjá'' (Old Norse for "King's mirror"; Latin: ''Speculum regale'', modern Norwegian: ''Kongsspegelen'' (Nynorsk) or ''Kongespeilet'' (Bokmål)) is a Norwegian didactic text in Old Norse from around 1250, an example of speculum lite ...
'' from AD 1230. The chronicler has heard about this phenomenon from compatriots returning from
Greenland
Greenland ( kl, Kalaallit Nunaat, ; da, Grønland, ) is an island country in North America that is part of the Kingdom of Denmark. It is located between the Arctic and Atlantic oceans, east of the Canadian Arctic Archipelago. Greenland is t ...
, and he gives three possible explanations: that the ocean was surrounded by vast fires; that the sun flares could reach around the world to its night side; or that
glacier
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...
s could store energy so that they eventually became
fluorescent
Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, tha ...
.
Walter William Bryant wrote in his book
''Kepler'' (1920) that
Tycho Brahe "seems to have been something of a
homœopathist, for he recommends
sulfur
Sulfur (or sulphur in British English) is a chemical element with the symbol S and atomic number 16. It is abundant, multivalent and nonmetallic. Under normal conditions, sulfur atoms form cyclic octatomic molecules with a chemical formula ...
to cure infectious diseases 'brought on by the sulphurous vapours of the Aurora Borealis.
In 1778,
Benjamin Franklin
Benjamin Franklin ( April 17, 1790) was an American polymath who was active as a writer, scientist, inventor, statesman, diplomat, printer, publisher, and political philosopher. Encyclopædia Britannica, Wood, 2021 Among the leading inte ...
theorized in his paper ''Aurora Borealis, Suppositions and Conjectures towards forming an Hypothesis for its Explanation'' that an aurora was caused by a concentration of electrical charge in the polar regions intensified by the snow and moisture in the air:
Observations of the rhythmic movement of compass needles due to the influence of an aurora were confirmed in the Swedish city of
Uppsala
Uppsala (, or all ending in , ; archaically spelled ''Upsala'') is the county seat of Uppsala County and the List of urban areas in Sweden by population, fourth-largest city in Sweden, after Stockholm, Gothenburg, and Malmö. It had 177,074 inha ...
by
Anders Celsius and
Olof Hiorter
Olof Petrus (or Peter) Hiorter (or Hjorter) (1696–1750) was a Swedish astronomer. After studying in the Netherlands, he was appointed lecturer at the University of Uppsala in 1732 to fill the vacant position of Anders Celsius then on his grand to ...
. In 1741, Hiorter was able to link large magnetic fluctuations with an aurora being observed overhead. This evidence helped to support their theory that 'magnetic storms' are responsible for such compass fluctuations.
![Aurora Borealis by Frederic Edwin Church](https://upload.wikimedia.org/wikipedia/commons/2/28/Aurora_Borealis_by_Frederic_Edwin_Church.jpg)
A variety of
Native American myths surround the spectacle. The European explorer
Samuel Hearne traveled with
Chipewyan Dene in 1771 and recorded their views on the ''ed-thin'' ('caribou'). According to Hearne, the Dene people saw the resemblance between an aurora and the sparks produced when
caribou
Reindeer (in North American English, known as caribou if wild and ''reindeer'' if domesticated) are deer in the genus ''Rangifer''. For the last few decades, reindeer were assigned to one species, ''Rangifer tarandus'', with about 10 subspe ...
fur is stroked. They believed that the lights were the spirits of their departed friends dancing in the sky, and when they shone brightly it meant that their deceased friends were very happy.
During the night after the
Battle of Fredericksburg
The Battle of Fredericksburg was fought December 11–15, 1862, in and around Fredericksburg, Virginia, in the Eastern Theater of the American Civil War. The combat, between the Union Army of the Potomac commanded by Maj. Gen. Ambrose Burnsi ...
, an aurora was seen from the battlefield. The
Confederate Army
The Confederate States Army, also called the Confederate Army or the Southern Army, was the military land force of the Confederate States of America (commonly referred to as the Confederacy) during the American Civil War (1861–1865), fighting ...
took this as a sign that God was on their side, as the lights were rarely seen so far south. The painting ''
Aurora Borealis'' by
Frederic Edwin Church
Frederic Edwin Church (May 4, 1826 – April 7, 1900) was an American landscape painter born in Hartford, Connecticut. He was a central figure in the Hudson River School of American landscape painters, best known for painting large landscapes, ...
is widely interpreted to represent the conflict of the
American Civil War
The American Civil War (April 12, 1861 – May 26, 1865; also known by other names) was a civil war in the United States. It was fought between the Union ("the North") and the Confederacy ("the South"), the latter formed by states th ...
.
A mid 19th-century British source says auroras were a rare occurrence before the 18th century. It quotes
Halley as saying that before the aurora of 1716, no such phenomenon had been recorded for more than 80 years, and none of any consequence since 1574. It says no appearance is recorded in the
''Transactions of the French Academy of Sciences'' between 1666 and 1716. And that one aurora recorded in ''Berlin Miscellany'' for 1797 was called a very rare event. One observed in 1723 at
Bologna
Bologna (, , ; egl, label= Emilian, Bulåggna ; lat, Bononia) is the capital and largest city of the Emilia-Romagna region in Northern Italy. It is the seventh most populous city in Italy with about 400,000 inhabitants and 150 different nat ...
was stated to be the first ever seen there.
Celsius
The degree Celsius is the unit of temperature on the Celsius scale (originally known as the centigrade scale outside Sweden), one of two temperature scales used in the International System of Units (SI), the other being the Kelvin scale. The ...
(1733) states the oldest residents of
Uppsala
Uppsala (, or all ending in , ; archaically spelled ''Upsala'') is the county seat of Uppsala County and the List of urban areas in Sweden by population, fourth-largest city in Sweden, after Stockholm, Gothenburg, and Malmö. It had 177,074 inha ...
thought the phenomenon a great rarity before 1716. The period between approximately 1645 to 1715 corresponds to the
Maunder minimum in sunspot activity.
In
Robert W. Service's satirical poem "
The Ballad of the Northern Lights" (1908) a Yukon prospector discovers that the aurora is the glow from a radium mine. He stakes his claim, then goes to town looking for investors.
In the early 1900s, the Norwegian scientist
Kristian Birkeland laid the foundation for current understanding of geomagnetism and polar auroras.
In
Sami mythology the northern lights are caused by the deceased who bled to death cutting themselves, their blood spilling on the sky, many aborigine peoples of northern Eurasia and North-America share similar beliefs of northern lights being the blood of the deceased, some believing they are caused by dead warriors' blood spraying on the sky as they engage in playing games, riding horses or having fun in some other way.
On other planets
![Saturns Northern Aurora still](https://upload.wikimedia.org/wikipedia/commons/b/b1/Saturns_Northern_Aurora_still.jpg)
Both
Jupiter
Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a mass more than two and a half times that of all the other planets in the Solar System combined, but ...
and
Saturn
Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...
have magnetic fields that are stronger than Earth's (Jupiter's equatorial field strength is 4.3
Gauss, compared to 0.3 Gauss for Earth), and both have extensive radiation belts. Auroras have been observed on both gas planets, most clearly using the
Hubble Space Telescope
The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
, and the
''Cassini'' and
''Galileo'' spacecraft, as well as on
Uranus
Uranus is the seventh planet from the Sun. Its name is a reference to the Greek god of the sky, Uranus (mythology), Uranus (Caelus), who, according to Greek mythology, was the great-grandfather of Ares (Mars (mythology), Mars), grandfather ...
and
Neptune
Neptune is the eighth planet from the Sun and the farthest known planet in the Solar System. It is the fourth-largest planet in the Solar System by diameter, the third-most-massive planet, and the densest giant planet. It is 17 times ...
.
The aurorae on Saturn seem, like Earth's, to be powered by the solar wind. However, Jupiter's aurorae are more complex. Jupiter's main auroral oval is associated with the plasma produced by the volcanic moon
Io, and the transport of this plasma within the planet's
magnetosphere
In astronomy and planetary science, a magnetosphere is a region of space surrounding an astronomical object in which charged particles are affected by that object's magnetic field. It is created by a celestial body with an active interior dynam ...
. An uncertain fraction of Jupiter's aurorae are powered by the solar wind. In addition, the moons, especially Io, are also powerful sources of aurora. These arise from electric currents along field lines ("field aligned currents"), generated by a dynamo mechanism due to the relative motion between the rotating planet and the moving moon. Io, which has active
volcanism
Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called ...
and an ionosphere, is a particularly strong source, and its currents also generate radio emissions, which have been studied since 1955. Using the Hubble Space Telescope, auroras over Io, Europa and Ganymede have all been observed.
Auroras have also been observed on
Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never fa ...
and
Mars
Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
. Venus has no magnetic field and so Venusian auroras appear as bright and diffuse patches of varying shape and intensity, sometimes distributed over the full disc of the planet. A Venusian aurora originates when electrons from the solar wind collide with the night-side atmosphere.
An aurora was detected on Mars, on 14 August 2004, by the SPICAM instrument aboard
Mars Express. The aurora was located at
Terra Cimmeria
Terra Cimmeria is a large Martian region, centered at and covering at its broadest extent. It covers latitudes 15 N to 75 S and longitudes 170 to 260 W. It lies in the Eridania quadrangle. Terra Cimmeria is one part of the heavily cratered, s ...
, in the region of 177° East, 52° South. The total size of the emission region was about 30 km across, and possibly about 8 km high. By analyzing a map of crustal magnetic anomalies compiled with data from
Mars Global Surveyor, scientists observed that the region of the emissions corresponded to an area where the strongest magnetic field is localized. This correlation indicated that the origin of the light emission was a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars.
Between 2014 and 2016, cometary auroras were observed on comet
67P/Churyumov–Gerasimenko by multiple instruments on the
Rosetta
Rosetta or Rashid (; ar, رشيد ' ; french: Rosette ; cop, ϯⲣⲁϣⲓⲧ ''ti-Rashit'', Ancient Greek: Βολβιτίνη ''Bolbitinē'') is a port city of the Nile Delta, east of Alexandria, in Egypt's Beheira governorate. The Ro ...
spacecraft.
The auroras were observed at
far-ultraviolet
Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...
wavelengths.
Coma
A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...
observations revealed atomic emissions of hydrogen and oxygen caused by the
photodissociation
Photodissociation, photolysis, photodecomposition, or photofragmentation is a chemical reaction in which molecules of a chemical compound are broken down by photons. It is defined as the interaction of one or more photons with one target molecule. ...
(not
photoionization, like in terrestrial auroras) of water molecules in the comet's coma.
The interaction of accelerated electrons from the solar wind with gas particles in the coma is responsible for the aurora.
Since comet 67P has no magnetic field, the aurora is diffusely spread around the comet.
Exoplanet
An exoplanet or extrasolar planet is a planet outside the Solar System. The first possible evidence of an exoplanet was noted in 1917 but was not recognized as such. The first confirmation of detection occurred in 1992. A different planet, init ...
s, such as
hot Jupiter
Hot Jupiters (sometimes called hot Saturns) are a class of gas giant exoplanets that are inferred to be physically similar to Jupiter but that have very short orbital periods (). The close proximity to their stars and high surface-atmosphere temp ...
s, have been suggested to experience ionization in their upper atmospheres and generate an aurora modified by
weather
Weather is the state of the atmosphere, describing for example the degree to which it is hot or cold, wet or dry, calm or stormy, clear or cloudy. On Earth, most weather phenomena occur in the lowest layer of the planet's atmosphere, the ...
in their turbulent
troposphere
The troposphere is the first and lowest layer of the atmosphere of the Earth, and contains 75% of the total mass of the planetary atmosphere, 99% of the total mass of water vapour and aerosols, and is where most weather phenomena occur. From ...
s. However, there is no current detection of an exoplanet aurora.
The first ever
extra-solar auroras were discovered in July 2015 over the
brown dwarf
Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most ...
star
LSR J1835+3259 LSR may refer to:
Computing
* Label switch router, a type of router located in the middle of an MPLS network
* '' Lego Stunt Rally'', a video game
* Link-state routing protocol, one of the two main classes of routing protocols used in packet switch ...
. The mainly red aurora was found to be a million times brighter than the Northern Lights, a result of the charged particles interacting with hydrogen in the atmosphere. It has been speculated that stellar winds may be stripping off material from the surface of the brown dwarf to produce their own electrons. Another possible explanation for the auroras is that an as-yet-undetected body around the dwarf star is throwing off material, as is the case with Jupiter and its moon Io.
See also
*
Airglow
*
Aurora (heraldry)
100px, Aurora in arm of Murmansk Oblast (on the silhouette of a trimount)">trimount.html" ;"title="Murmansk Oblast (on the silhouette of a trimount">Murmansk Oblast (on the silhouette of a trimount)
Aurora is used as a charge in heraldry. The u ...
*
Heliophysics
*
List of plasma physics articles
*
List of solar storms
*
Paschen's law
*
Space tornado
A space tornado is a solar windstorm and is exceptionally larger and more powerful than conventional tornadoes on Earth. They are also thought to produce the ''aurora borealis'' phenomenon.
Tornadoes on Earth are formed within the atmosphere by ...
*
Space weather
Explanatory notes
References
Further reading
* This includes a highly detailed description of historical observations and descriptions.
*
*
*
*
*
*
Alt URL*
*
*
*
External links
Aurora forecast – Will there be northern lights?Current global map showing the probability of visible auroraAurora – ForecastingOfficial MET aurora forecasting in IcelandAurora Borealis – Predicting– Online Converter – ''Northern Lights'' Latitude.
Aurora Service Europe– Aurora forecasts for Europe.
Live Northern Lights webstreamWorld's Best Aurora – The Northwest Territories is the world's Northern Lights mecca.
Multimedia
Amazing time-lapse video of Aurora Borealis– Shot in Iceland over the winter of 2013/2014.
Popular video of Aurora Borealis– Taken in Norway in 2011.
Aurora Photo Gallery– Views taken 2009–2011.
– "Full-Sky Aurora" over Eastern
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
. December 2011.
Videos and Photos – Auroras at Night
Video (04:49)– Aurora Borealis – How The ''Northern Lights'' Are Created.
Video (47:40)– ''Northern Lights'' – Documentary.
Video (5:00)– Northern lights video in real time
Video (01:42)– ''Northern Light – Story of
Geomagnetc Storm (
Terschelling Island – 6/7 April 2000).
Video (01:56)(Time-Lapse) − Auroras – Ground-Level View from
Finnish Lapland
Lapland ( fi, Lappi ; se, Lappi; smn, Laapi; sv, Lappland; la, Lapponia, links=no) is the largest and northernmost region of Finland. The 21 municipalities in the region cooperate in a Regional Council. Lapland borders the region of North O ...
2011.
Video (02:43)(Time-Lapse) − Auroras – Ground-Level View from
Tromsø
Tromsø (, , ; se, Romsa ; fkv, Tromssa; sv, Tromsö) is a List of municipalities of Norway, municipality in Troms og Finnmark county, Norway. The administrative centre of the municipality is the Tromsø (city), city of Tromsø.
Tromsø lies ...
,
Norway
Norway, officially the Kingdom of Norway, is a Nordic country in Northern Europe, the mainland territory of which comprises the western and northernmost portion of the Scandinavian Peninsula. The remote Arctic island of Jan Mayen and t ...
. 24 November 2010.
Video (00:27)(Time-Lapse) –
Earth
Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
and Auroras – Viewed from
The International Space Station.
{{DEFAULTSORT:Aurora
Space plasmas
Polar regions of the Earth
Atmospheric optical phenomena
Earth phenomena
Electrical phenomena
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Planetary science
Sources of electromagnetic interference
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Space weather
Geomagnetism