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Encyclopedia > Aurora (phenomenon)
Aurora borealis
Aurora borealis
Aurora borealis
Aurora borealis
For other uses, see Aurora (disambiguation).

The aurora is a glow observed in the night sky, usually in the polar zone. For this reason scientists sometimes call it a "polar aurora" (or "aurora polaris"). In northern latitudes, it is known as "aurora borealis" which is Latin for "northern dawn" since in Europe especially, it often appears as a reddish glow on the northern horizon as if the sun were rising from an unusual direction. The aurora borealis is also called the "northern lights". The aurora borealis most often occurs from September to October and March to April. Its southern counterpart, "aurora australis", has similar properties. Image File history File links Download high resolution version (1024x696, 51 KB) Summary Photo by Craig M. Groshek Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high resolution version (1024x696, 51 KB) Summary Photo by Craig M. Groshek Licensing File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Polarlicht. ... Image File history File links Polarlicht. ... // Arts Literature Aurora (comics), superhero in the Marvel Universe Aurora (planet), Spacer world in Isaac Asimovs fiction Aurora Award (Prix Aurora), Canadian science-fiction and fantasy Aurora consurgens, manuscripts Aurora Leigh, a lengthy poem by Elizabeth Barrett Browning Aurora, SF society, a science fiction & fantasy society from Rijeka, Croatia...

Contents


Auroral mechanism

The aurora is now known to be caused by electrons of typical energy of 1-15 keV, i.e. the energy obtained by the electrons passing through a voltage difference of 1,000-15,000 volts. The light is produced when they collide with atoms of the upper atmosphere, typically at altitudes of 80-150 km. It tends to be dominated by emissions of atomic oxygen--the greenish line at 557.7 nm and (especially with electrons of lower energy and higher altitude) the dark-red line at 630.0 nm. Both these represent "forbidden" transitions of atomic oxygen from energy levels which (in absence of collisions) persist for a long time, accounting for the slow brightening and fading (0.5-1 sec) of auroral rays. Many other lines can also be observed, especially those of molecular nitrogen, and these vary much faster, revealing the true dynamic nature of the aurora.


Auroras can also be observed in the ultra-violet (UV) light, a very good way of observing it from space (but not from ground--the atmosphere absorbs UV). The "Polar" spacecraft even observed it in X-rays. The image is very rough, but precipitation of high-energy electrons can be identified.


Auroral forms and magnetism

A corona
A corona

Typically the aurora appears either as a diffuse glow or as "curtains" that approximately extend in the east-west direction. At some times, they form "quiet arcs", at others ("active aurora") they evolve and change constantly. Each curtain consists of many parallel rays, each lined up with the local direction of the magnetic field lines, suggesting that aurora is shaped by the Earth's magnetic field, Indeed, satellites show auroral electrons to be guided by magnetic field lines, spiraling around them while moving earthwards. Image File history File links Aurora2. ... Image File history File links Aurora2. ... This article or section does not cite its references or sources. ...


The curtains often show folds called "striations". When the field line guiding a bright auroral patch leads to a point directly above the observer, the aurora may appear as a "corona" of diverging rays, an effect of perspective.


In 1741 Hiorter and Celsius first noticed other evidence for magnetic control, namely, large magnetic fluctuations occurred whenever the aurora was observed overhead. This indicates (it was later realized) that large electric currents were associated with the aurora, flowing in the region where auroral light originated. Kristian Birkeland (1903) deduced that the currents flowed in the east-west directions along the auroral arc, and such currents, flowing from the dayside towards (approximately) midnight were later named "auroral electrojets" (see also Birkeland currents). A degree Celsius (°C) is a unit of temperature named after the Swedish astronomer Anders Celsius (1701-1744), who first proposed a similar system in 1742. ... In electricity, current refers to electric current, which is the flow of electric charge. ... Kristian Birkeland Kristian Birkeland (December 13, 1867 - June 15, 1917) was born in Christiania (Oslo today) and wrote his first scientific paper at the age of 18. ... The aurora on Jupiter, powered by Jovian Birkeland currents [Ref. ...


Still another evidence for a magnetic connection are the statistics of auroral observations. Elias Loomis (1860) and later in more detail Hermann Fritz (1881) established that the aurora appeared mainly in the "auroral zone", a ring-shaped region of approx. radius 2500 km around the magnetic pole of the Earth, not its geographic one. It was hardly ever seen near that pole itself. The instantaneous distribution of auroras ("auroral oval", Yasha Feldstein 1963) is slightly different, centered about 3-5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest equatorward around midnight.

Aurora australis
Aurora australis

Image File history File links Download high resolution version (5109x1200, 412 KB) Aurora Australis appearing in the night sky (10:50 pm Australian time (GMT = 8:50 am) at Swifts Creek, 100km north of Lakes Entrance, Victoria, Australia. ... Image File history File links Download high resolution version (5109x1200, 412 KB) Aurora Australis appearing in the night sky (10:50 pm Australian time (GMT = 8:50 am) at Swifts Creek, 100km north of Lakes Entrance, Victoria, Australia. ...

Frequency of occurrence

Aurora australis 1994 from latitude 47 degrees south
Aurora australis 1994 from latitude 47 degrees south

The aurora is a common occurrence in the ring-shaped zone. It is occasionally seen in temperate latitudes, when a strong magnetic storm temporarily expands the auroral oval. Large magnetic storms are most common during the peak of the 11-year sunspot cycle, or during the 3 years after that peak. However, within the auroral zone the likelihood of an aurora occurring depends mostly on the slant of interplanetary magnetic field lines (further below), being greater with southward slants. Image File history File links AuroraAustralisPaulMoss. ... Image File history File links AuroraAustralisPaulMoss. ... A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings and intense magnetic activity, which inhibits convection, forming areas of low surface temperature. ...


Geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes -- that is, early autumn and spring. It's a bit puzzling because polar activity normally does not depend on the Earth's seasons. Why should geomagnetic storms?


"We've known about this seasonal effect for more than 100 years," says Dennis Gallagher, a space physicist at the NASA Marshall Space Flight Center. "Some aspects of it are understood, but not all." Spring and autumn are good times to spot Northern Lights, and scientists would like to know why. "At such times the two fields (Earth's and the IMF) link up," says Christopher Russell, a Professor of Geophysics and Space Physics at UCLA. "You can then follow a magnetic field line from Earth directly into the solar wind." South-pointing Bz's open a door through which energy from the solar wind can reach Earth's inner magnetosphere.


In the early 1970s Russell and colleague R. L. McPherron recognized a connection between Bz and Earth's changing seasons: The average size of Bz is greatest each year in early Spring and Autumn. What remains is a puzzle that space scientists are still trying to solve. "This is an area of active research," notes Tony Lui, a space physicist at the Johns Hopkins University Applied Physics Lab. "We don't have all the answers yet, because it's a complicated problem." ref NASA


The solar wind and magnetosphere

Schematic of Earth's magnetosphere
Schematic of Earth's magnetosphere

The Earth is constantly immersed in the solar wind, a rarefied flow of hot [1] plasma (gas of free electrons and positive ions) emitted by the sun in all directions, a result of the million-degree heat of the sun's outermost layer, the solar corona. The solar wind usually reaches Earth with a velocity around 400 km/s, density around 5 ions/cc and magnetic field intensity around 2–5 nT (nanoteslas; the Earth's surface field is typically 30,000–50,000 nT). These are typical values. During magnetic storms, in particular, flows can be several times faster; the interplanetary magnetic field (IMF) may also be much stronger. Image File history File links Schematic of magnetosphere. ... Image File history File links Schematic of magnetosphere. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ... The corona is the luminous plasma atmosphere of the Sun extending millions of kilometres into space, most easily seen during a total solar eclipse, but also observable in a coronagraph. ... The tesla (symbol T) is the SI derived unit of magnetic flux density (or magnetic induction). ...


The IMF originates on the sun, related to the field of sunspots, 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 skews them (at Earth) by about 45 degrees, so that field lines passing Earth may actually start near the western edge ("limb") of the visible sun. A sunspot is a region on the Suns surface (photosphere) that is marked by a lower temperature than its surroundings and intense magnetic activity, which inhibits convection, forming areas of low surface temperature. ... In physics, magnetism is one of the phenomena by which materials exert an attractive or repulsive force on other materials. ...


The Earth's "magnetosphere" is the space region dominated by its magnetic field. It forms an obstacle in the path of the solar wind, causing it to be diverted around it, at a distance of about 70,000 km (before it reaches that boundary, typically 12,000–15,000 km upstream, a bow shock forms). The width of the magnetospheric obstacle, abreast of Earth is typically 190,000 km, and on the night side a long "magnetotail" of stretched field lines extends to great distances. Schematic of Earths magnetosphere. ... In a planetary magnetosphere, the bow shock is the boundary at which the solar wind abruptly drops as a result of its approach to the magnetopause. ...


The origin of the aurora

Aurora australis (September 11, 2005) as captured by NASA's IMAGE satellite.
Enlarge
Aurora australis (September 11, 2005) as captured by NASA's IMAGE satellite.

The ultimate energy source of the aurora is undoubtedly the solar wind flowing past the Earth. For images in Wikipedia, see Wikipedia:Images. ...


Both the magnetosphere and the solar wind consist of plasma, which can conduct electricity. It is well known (since Faraday's work around 1830) that if two electric conductors are immersed in a magnetic field and one moves relative to the other, while a closed electric circuit exists which threads both conductors, then an electric current will (usually) arise in that circuit. Electric generators of dynamos make use of this process ("the dynamo effect"), but the conductors can also be plasmas or other fluids. A Plasma lamp, illustrating some of the more complex phenomena of a plasma, including filamentation A solar coronal mass ejection blasts plasma throughout the solar system. ... In physics, the faraday (not to be confused with the farad) is a unit of electrical charge; one faraday is equal to the charge of 6. ... The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ...


In particular the solar wind and the magnetosphere are two electrically conducting fluids with such relative motion, and should be able (in principle) to generate electric currents by "dynamo action", in the process also extracting energy from the flow of the solar wind. The process is hampered by the fact plasmas conduct easily along magnetic field lines but not so perpendicular to them. It is therefore important that a temporary interconnection be established between the field lines of the solar wind and those of the magnetosphere, by a process known as magnetic merging or reconnection. It happens most easily with a southward slant of interplanetary field lines, because then field lines north of Earth approximately match the direction of field lines near the north magnetic pole (namely, into the earth), and similarly near the southern pole. Indeed, active auroras (and related "substorms") are much more likely at such times.


Electric currents originating in such fashion apparently give auroral electrons their energy. The magnetospheric plasma has an abundance of electrons: some are magnetically trapped, some reside in the magnetotail, and some exists in the upwards extension of the ionosphere, which may extend (with diminishing density) some 25,000 km around the Earth. Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... Schematic of Earths magnetosphere. ... Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ...


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 such currents require a driving voltage, which some 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. The aurora on Jupiter, powered by Jovian Birkeland currents [Ref. ... Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ... Relationship of the atmosphere and ionosphere The ionosphere is the part of the atmosphere that is ionized by solar radiation. ... A voltage source, V, drives an electric current I through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law, named after its discoverer Georg Ohm [1], states that the potential difference between two points along a connected path (i. ...


Ionospheric resistance has a complex nature, and leads to a secondary "Hall current" 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" (AE) index (measured in nanotesla) is regularly derived from ground data, and serves as a general measure of auroral activity. The Hall effect refers to the potential difference (voltage) on opposite sides of a thin sheet of conducting or semiconducting material in the form of a Hall bar or a van der Pauw element through which an electric current is flowing, created by a magnetic field applied perpendicular to the...


However, ohmic resistance is not the only obstacle to current flow in this circuit. The convergence of magnetic field lines near Earth creates a "mirror effect" which turns back most of the down-flowing electrons (where currents flow upwards), inhibiting current-carrying capacity. To overcome this, part of the available voltage appears along the field line ("parallel to the field"), helping electrons overcome that obstacle by widening the bundle of trajectories reaching Earth; a similar "parallel voltage" is used in "tandem mirror" plasma containment devices. A feature of such voltage is that it is concentrated near Earth (potential proportional to field intensity; Persson, 1963) and indeed, as deduced by Evans (1974) and confirmed by satellites, most auroral acceleration occurs below 10,000 km. Another indicator of "parallel electric fields" along field lines are beams of upwards flowing O+ ions observed on auroral field lines. A voltage source, V, drives an electric current I through resistor, R, the three quantities obeying Ohms law: V = IR Ohms law, named after its discoverer Georg Ohm [1], states that the potential difference between two points along a connected path (i. ...


While this mechanism is probably the main source of the familiar auroral arcs, formations conspicuous from the ground, more energy might go to other, less prominent types of aurora, e.g. the diffuse aurora (below) and the low-energy electrons precipitated in magnetic storms (also below).


Some O+ ions ("conics") also seem accelerated in different ways by plasma processes associated with the aurora. These ions are accelerated by plasma waves, in directions mainly perpendicular to the field lines. They therefore start at their own "mirror points" and can travel only upwards. As they do so, the "mirror effect" transforms their directions of motion, from perpendicular to the line to lying on a cone around it, which gradually narrows down.)


In addition, the aurora and associated currents produce a strong radio emission around 150 kHz (AKR or "auroral kilometric radiation") discovered in 1972. Ionospheric absorption makes AKR observable from space only.


These "parallel voltages" accelerate electrons to auroral energies and seem to be a major source of aurora. Other mechanisms have also been proposed, in particular, Alfvén waves, wave modes involving the magnetic field first noted by Hannes Alfvén (1942), which have been observed in the lab and in space. The question is however whether this might just be a different way of looking at the above process, because this approach does not point out a different energy source, and many plasma bulk phenomena can also be described in terms of Alfvén waves. A cluster of double layers forming in an Alfvén wave, about a sixth of the distance from the left. ... Hannes Olof Gösta Alfvén (May 30, 1908; Norrköping, Sweden - April 2, 1995; Djursholm, Sweden) was a Swedish electrical power engineer. ...


Other processes are also involved in the aurora, and much remains to be learned. Auroral electrons created by large magnetic storms often seem to have energies below 1 keV, and are stopped higher up, near 200 km. Such low energies excite mainly the red line of oxygen, so that often such auroras are red. On the other hand, positive ions also reach the ionosphere at such time, with energies of 20-30 keV, suggesting they might be an "overflow" along magnetic field lines of the copious "ring current" ions accelerated at such times, by processes different from the ones described above. A geomagnetic storm is a temporary disturbance of the Earths magnetosphere. ...

Image File history File links Aurora_Borealis_from_Expedition_6. ...

Sources and types of aurora

Again, our understanding is very incomplete. A rough guess may point out three main sources:

  1. Dynamo action with the solar wind flowing past Earth, possibly producing quiet auroral arcs ("directly driven" process). The circuit of the accelerating currents and their connection to the solar wind are uncertain.
  2. Dynamo action involving plasma squeezed earthward by sudden convulsions of the magnetotail ("magnetic substorms"). Substorms tend to occur after prolonged spells (hours) during which the interplanetary magnetic field has an appreciable southward component, leading to a high rate of interconnection between its field lines and those of Earth. As a result the solar wind moves magnetic flux (tubes of magnetic field lines, moving 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 causing it to be squeezed harder. Ultimately the tail plasma is torn ("magnetic reconnection") --some blobs ("plasmoids") are squeezed tailwards and are carried away with the solar wind, others are squeezed earthwards where their motion feeds large outbursts of aurora, mainly around midnight ("unloading process").

    Magnetic storms have similar effects, but with greater vigor. The big difference is the addition of many particles to the plasma trapped around Earth, enhancing the "ring current" which it carries. The resulting modification of the Earth's field allows aurora to be visible at middle latitudes, on field lines much closer to the equator. The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ... The Dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a magnetic field. ... Schematic of Earths magnetosphere. ... A geomagnetic storm is a temporary disturbance of the Earths magnetosphere. ...

  3. Satellite images of the aurora from above show a "ring of fire" along the auroral oval (see above), often widest at midnight. That is the "diffuse aurora", not distinct enough to be seen by the eye. It does not seem to be associated with acceleration by electric currents (although currents and their arcs may be embedded in it) but to be due to electrons leaking out of the magnetotail.

Any magnetic trapping is leaky--there always exists a bundle of directions ("loss cone") around the guiding magnetic field lines where particles are not trapped but escape. In the radiation belts of Earth, once particles on such trajectories are gone, new ones only replace them very slowly, leaving such directions nearly "empty". In the magnetotail, however, particle trajectories seem to be constantly reshuffled, probably when the particles cross the very weak field near the equator. As a result the flow of electrons in all directions is nearly the same ("isotropic"), and that assures a steady supply of leaking electrons. Image File history File links DEaurora. ... Van Allen radiation belts The Van Allen radiation belt is a torus of energetic charged particles ( a plasma) around Earth, trapped by Earths magnetic field. ...


The energization of such electrons comes from magnetotail processes. The leakage of negative electrons does not leave the tail positively charged, because each leaked the electron lost to the atmosphere is quickly replaced by a low energy electron drawn upwards from the ionosphere. Such replacement of "hot" electrons by "cold" ones is in complete accord with the 2nd law of thermodynamics. The second law of thermodynamics, in its most concise form, states that the total entropy of any isolated thermodynamic system tends to increase over time, approaching a maximum value. ...


Other types of aurora have been observed from space, e.g. "poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Space does not allow discussion of other effects such as flickering aurora, "black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) has been observed around the two polar cusps, the "funnels" of field lines separating the ones that close on the day side of Earth from lines swept into the tail. The cusps allow a small amount of solar wind to reach the top of the atmosphere, producing an auroral glow.


Auroras on other planets

Jupiter aurora. The bright spot at far left is the end of field line to Io, spots at bottom lead to Ganymede and Europa
Jupiter aurora. The bright spot at far left is the end of field line to Io, spots at bottom lead to Ganymede and Europa

Both Jupiter and Saturn have magnetic fields much stronger than Earth's (Uranus, Neptune and Mercury are also magnetic), and both have large radiation belts. Aurora has been observed on both, most clearly with the Hubble telescope. Image File history File links Jupiter. ... Image File history File links Jupiter. ... Atmospheric characteristics Atmospheric pressure 70 kPa Hydrogen ~86% Helium ~14% Methane 0. ... Atmospheric characteristics Atmospheric pressure 140 kPa Hydrogen >93% Helium >5% Methane 0. ...


These auroras seem, like Earth's, to be powered by the solar wind. In addition, however, Jupiter's moons, especially Io, are also powerful sources of auroras. These arise from electric currents along field lines ("field aligned currents"), generated by a dynamo mechanism due to relative motion between the rotating planet and the moving moon. Io, which has active volcanism and an ionosphere, is a particularly strong source, and its currents also generate radio emissions, studied since 1955. Atmospheric characteristics Atmospheric pressure trace Sulfur dioxide 90% Io (eye-oe, IPA: , Greek Ῑώ) is the innermost of the four Galilean moons of Jupiter. ...


An aurora has recently been detected on Mars, even though it was thought that the lack of a strong magnetic field would not make one possible. [2]


Obsolete theories

  • Auroral electrons come from beams emitted by the sun. That was claimed around 1900 by Kristian Birkeland, whose experiments in a vacuum chamber with electron beams and magnetized spheres (miniature models of the Earth or "terrellas") showed that such electrons would be guided towards the polar regions. Problems with this model included absence of aurora at the poles themselves, self-dispersal of such beams by their negative charge, and more recently, lack of any observational evidence in space.
  • The aurora is the overflow of the radiation belt ("leaky bucket theory"). This was first disproved around 1962 by James Van Allen and co-workers, who showed that the high rate at which energy was dissipated by the aurora would quickly drain all that was available in the radiation belt. Soon afterwards it became clear that most of the energy in trapped particles resided in positive ions, while auroral particles were almost always electrons, of relatively low energy.
  • The aurora is produced by solar wind particles guided by the Earth's field lines to the top of the atmosphere. That holds true for the cusp aurora, but outside the cusp, the solar wind has no direct access. In addition, the main energy in the solar wind resides in positive ions; electrons only have about 0.5 eV (electron volt), and while in the cusp this may be raised to 50–100 eV, that still falls short of auroral energies.

Kristian Birkeland Kristian Birkeland (December 13, 1867 - June 15, 1917) was born in Christiania (Oslo today) and wrote his first scientific paper at the age of 18. ... Van Allen radiation belts The Van Allen radiation belt is a torus of energetic charged particles ( a plasma) around Earth, trapped by Earths magnetic field. ... James Van Allen at National Air & Space Museum (NASM), 1981, Photo courtesy of NASM. Explorer I model and Pioneer H probe in background James Alfred Van Allen (born September 7, 1914) is considered Americas foremost space scientist. ... The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ...

Auroral sounds

Throughout history people have written and spoken of sounds associated with auroral displays, often describing them as crackling, hissing, buzzing, or whistling. Danish explorer Knud Rasmussen mentioned them indirectly in 1932 while describing the folk traditions of Greenland Eskimos. The same sounds in the same context are mentioned in an account written by Canadian anthropologist Ernest Hawkes in 1916. Cornelius Tacitus (AD 56-120), an ancient Roman historian, wrote that people from the north of (modern) Germany claimed to hear them. Knud Johan Victor Rasmussen (June 7, 1879–December 21, 1933) was a Greenlandic polar explorer and anthropologist. ... 1932 (MCMXXXII) was a leap year starting on Friday (the link will take you to a full 1932 calendar). ... Inuit (ᐃᓄᐃᑦ, singular Inuk or Inuq / ᐃᓄᒃ) is a general term for a group of culturally similar indigenous peoples of the Arctic who descended from the Thule. ... Anthropology (from the Greek word άνθρωπος, human or person) consists of the study of humanity (see genus Homo). ... 1916 (MCMXVI) was a leap year starting on Saturday (link will take you to calendar). ... This article is about the historian Tacitus. ... Dionysius Exiguus invented Anno Domini years to date Easter. ... For other uses, see number 56. ... For other uses, see number 120. ... The Roman Forum was the central area around which ancient Rome developed. ...


Today, many people continue to report these sounds, but despite their many anecdotal reports, nobody has yet managed to record the sounds, and there are scientific problems with the idea of the sounds being true sound waves originating in the auroras. The energy of the auroras and other factors make it extremely improbable that any sounds directly produced by auroral discharges would reach the ground, and the coincidence of sounds with the visible changes in the auroras conflicts with the necessary propagation time for any sounds from the discharges themselves. Some people speculate that local electrostatic phenomena induced by the auroras might explain the sounds; theories associated with brush discharges seem to fit the reported observations best, although no theory thus far provides a completely satisfactory explanation.


Aurora in folklore

In Bulfinch's Mythology from 1855 by Thomas Bulfinch there is the claim that in Norse mythology: Thomas Bulfinch (July 15, 1796 - May 27, 1867) was an American writer, born in Newton, Massachusetts to a highly-educated but not rich Bostonian merchant family. ... 1855 was a common year starting on Monday (see link for calendar). ... Thomas Bulfinch (July 15, 1796 - May 27, 1867) was an American writer, born in Newton, Massachusetts to a highly-educated but not rich Bostonian merchant family. ... Norse or Scandinavian mythology comprises the pre-Christian religion, beliefs and legends of the Scandinavian people, including those who settled on Iceland, where the written sources for Norse mythology were assembled. ...

The Valkyrior are warlike virgins, mounted upon horses and armed with helmets and spears. /.../ When they ride forth on their errand, their armour sheds a strange flickering light, which flashes up over the northern skies, making what men call the "aurora borealis", or "Northern Lights". [3]

While a striking notion, there is nothing in the Old Norse literature supporting this assertion. Although auroral activity is common over Scandinavia and Iceland today, it is possible that the Magnetic North Pole was considerably further away from this region during the centuries before the documentation of Norse mythology, thus explaining the absent references. [4] A statue from 1908 by Stephan Sinding located in Copenhagen, presents an active image of a valkyrie. ...


The first Old Norse account of norðurljós is instead found in the Norwegian chronicle Konungs Skuggsjá from AD 1250. The chronicler has heard about this phenomenon from compatriots returning from Greenland, 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 glaciers could store energy so that they eventually became fluorescent. [5] A page from Konungs skuggsjá. Konungs skuggsjá (Old Norse for Kings mirror; Latin: Speculum regale, modern Norwegian: Kongespeilet) is a Norwegian educational scripture from around 1250, dealing with politics and moral. ... Aletsch glacier, Switzerland A glacier is a large, long-lasting river of ice that is formed on land and moves in response to gravity. ... Fluorescence induced by exposure to ultraviolet light in vials containing various sized Cadmium selenide (CdSe) quantum dots. ...


An old Scandinavian name for northern lights translates as herring flash. It was believed that northern lights were the reflections cast by large swarms of herring onto the sky. Scandinavia is a region in Northern Europe named after the Scandinavian Peninsula. ... Species Clupea alba Clupea bentincki Clupea caspiopontica Clupea chrysotaenia Clupea elongata Clupea halec Clupea harengus Clupea inermis Clupea leachii Clupea lineolata Clupea minima Clupea mirabilis Clupea pallasii Clupea sardinacaroli Clupea sulcata Herrings are small oily fish of the genus Clupea found in the temperate, shallow waters of the North Atlantic...


Another Scandinavian source refers to 'the fires that surround the North and South edges of the world'. This has been put forward as evidence that the Norse ventured as far as Antarctica, although this is pure conjecture.


The Finnish name for northern lights is revontulet, fox fires. According to legend, foxes made of fire lived in Lapland, and revontulet were the sparks they whisked up into the atmosphere with their tails. // A Red Fox (Vulpes vulpes) A fox is a member of any of 27 species of small omnivorous canids. ... National anthem Sámi soga lávlla Languages Sami, Norwegian, Swedish, Finnish, Russian Area ca. ...


The Sami people believed that one should be particularly careful and quiet when observed by the guovssahasat. The Sami people (also Sámi, Saami, Lapps and Laplanders) are the indigenous people of Sápmi, which encompasses parts of northern Sweden, Norway, Finland and the Kola Peninsula of Russia. ...


In Inuit folklore, northern lights were the spirits of the dead playing football with a walrus skull over the sky. Inuit (Inuktitut syllabics: ᐃᓄᐃᑦ, singular Inuk or Inuq / ᐃᓄᒃ) is a general term for a group of culturally similar indigenous peoples inhabiting the Arctic coasts of Siberia, Alaska, the Northwest Territories, Nunavut, Quebec, Labrador and Greenland. ... The English word spirit comes from the Latin spiritus, meaning breath. ... Binomial name Odobenus rosmarus (Linnaeus, 1758) Subspecies Walruses (From Dutch: wal meaning shore,and r(e)us meaning giant. ...


In Latvian folklore northern lights, especially if red and observed in winter, are believed to be fighting souls of dead warriors, an omen foretelling disaster (especially war or famine). Red is any of a number of similar colors at the lowest frequencies of light discernible by the human eye. ... Winter is one of the four seasons of temperate zones. ... This page is about the core essence of a being. ... This page deals with the cessation of life. ... A warrior is a person habitually engaged in combat. ... This article is about Omens as divinatory portents. ... The only atomic weapons ever used in war - the atomic bombing of Nagasaki, Japan by the United States on August 9, 1945, effectively ending World War II. The bombs over Hiroshima (August 6) and Nagasaki immediately killed over 120,000 people. ... A famine is a phenomenon in which a large percentage of the population of a region or country are so undernourished that death by starvation becomes increasingly common. ...


In Scotland, the northern lights were known as "the merry dancers" or na fir-chlis. There are many old sayings about them, including the Scottish Gaelic proverb "When the merry dancers play, they are like to slay." The playfulness of the merry dancers was supposed to end occasionally in quite a serious fight, and next morning when children saw patches of red lichen on the stones, they say amongst themselves that "the merry dancers bled each other last night". The appearance of these lights in the sky was considered a sign of the approach of unsettled weather. Motto: Nemo me impune lacessit (English: No one provokes me with impunity) Scotlands location within Europe Scotlands location within the United Kingdom Languages English, Gaelic, Scots Capital Edinburgh Largest city Glasgow First Minister Jack McConnell Area - Total - % water Ranked 2nd UK 78,782 km² 1. ... An adage is a short, but memorable saying, which holds some important fact of experience that is considered true by many people, or it has gained some credibility through its long use. ... Note: This page contains phonetic information presented in the International Phonetic Alphabet (IPA) using Unicode. ... A proverb (from the Latin proverbium) is a pithy saying which gained credence through widespread or frequent use. ... A fight is an act to establish dominance over an opposition by causing harm by physical or mental damage. ... A male Caucasian toddler child A child (plural: children) is a young human. ... Crustose and foliose lichens on a wall A foliose lichen on basalt. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... Find more information on Weather by searching Wikipedias sister projects: Dictionary definitions from Wiktionary Textbooks from Wikibooks Quotations from Wikiquote Source texts from Wikisource Images and media from Commons News stories from Wikinews Weather is an all-encompassing term used to describe all of the many and varied phenomena...


See also

This page is a list of sources of light. ...

References

  • "Secrets of the Polar Aurora"
  • "Exploration of the Earth's magnetosphere" - overview of the magnetosphere, including auroras; and including extensive bibliographies of scientific articles
  • Robert H. Eather, Majestic Lights, American Geophysical Union, Washington, DC, 1980 (323 pages)
  • Syun-Ichi Akasofu, “Secrets of the Aurora Borealis”, Alaska Geographic Series, Volume 29, No. 1, Graphic Arts Center Publishing Company, April 2002
  • Candace S. Savage, Aurora: The Mysterious Northern Lights, Firefly Books, July 2001 (144 pages)

External links

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Aurora Watch, at the university of Lancshire, gives email warnings of coronal mass ejections and geomagnetic storms for aurora watching enthusiasts: http://www.dcs.lancs.ac.uk/iono/aurorawatch/cgi-bin/subscribe Image File history File links Commons-logo. ... The Wikimedia Commons (also called Commons or Wikicommons) is a repository of free content images, sound and other multimedia files. ...


 
 

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