Auroras (North/South Polar Lights; or aurorae, sing.: aurora) are natural colored light displays in the sky, usually observed at night, particularly in the polar zone. Bear Lake (one of a dozen Lakes by this name in Alaska is near the town of Seward and Resurrection Bay, in the Kenai Peninsula Borough Fairbanks (ˈfɛrbæŋks is a Home Rule City in Fairbanks North Star Borough, Alaska, United States. SINGULAR is a Computer algebra system for Polynomial computations with special emphasis on the needs of Commutative algebra, Algebraic geometry The sky is the part of the Atmosphere or of Outer space visible from the surface of any Astronomical object. A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based They typically occur in the ionosphere. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation Some scientists call them "polar auroras" (or "aurorae polares"). In northern latitudes, the effect is known as the aurora borealis, named after the Roman goddess of dawn, Aurora, and the Greek name for north wind, Boreas. Latitude, usually denoted symbolically by the Greek letter phi ( Φ) gives the location of a place on Earth (or other planetary body north or south of the Ancient Rome was a Civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC Roman mythology, or more appropriately Latin mythology, refers to the mythological beliefs of the Italic people inhabiting the region of Latium and its Dawn refers to the Twilight before Sunrise. It is recognized by the presence of weak sunlight while the sun itself is still below the horizon This article is about the Roman goddess of dawn for the asteroid see 94 Aurora. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Wind is the flow of Air or other Gases that compose an Atmosphere (including but not limited to the Earth's) In Greek Mythology, the Anemoi (in Greek, Άνεμοι &mdash " winds " were Wind gods who were each ascribed It often appears as a greenish glow or sometimes a faint red, as if the sun was rising from an unusual direction. The aurora borealis is also called the northern polar lights, as it is only visible in the North sky from the Northern Hemisphere. Earth's polar regions are the areas of the globe surrounding the poles also known as frigid zones. Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' The aurora borealis most often occurs from September to October and from March to April. The Cree call this phenomenon the Dance of the Spirits. Not to be confused with the Creek. Cree is an Exonym applied to various people indigenous to North America namely the Nehiyaw Nehithaw Nehilaw

Its southern counterpart, the aurora australis/southern polar lights, has similar properties. Australis is the Latin word for "of the South". Latin ( lingua Latīna, laˈtiːna is an Italic language, historically spoken in Latium and Ancient Rome.

Benjamin Franklin first brought attention to the "mystery of the Northern Lights. " He theorized the shifting lights to a concentration of electrical charges in the polar regions intensified by the snow and other moisture[1].

Contents 1 Auroral mechanism 2 Auroral forms and magnetism 3 Solar wind and magnetosphere 4 Frequency of occurrence 4.1 Auroral events of historical significance 5 Origin 6 Sources and types 6.1 Magnetic ropes 7 On other planets 8 History of Aurora theories 9 Images 10 In folklore 11 References 11.1 Footnotes 12 See also 13 External links

Auroral mechanism

Auroras are produced by the collision of charged particles from Earth's magnetosphere, mostly electrons but also protons and heavier particles, with atoms and molecules of Earth's upper atmosphere (at altitudes above 80 km). EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J The proton ( Greek πρῶτον / proton "first" is a Subatomic particle with an Electric charge of one positive History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " The kilometre ( American spelling: kilometer) symbol km is a unit of Length in the Metric system, equal to one thousand The particles have energies of 1 to 100 keV. They originate from the Sun and arrive at the vicinity of Earth in the relatively low-energy solar wind. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. When the trapped magnetic field of the solar wind is favourably oriented (principally southwards) it reconnects with Earth's magnetic field, and solar particles enter the magnetosphere and are swept to the magnetotail. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges Further magnetic reconnection accelerates the particles towards Earth.

The collisions in the atmosphere electronically excite atoms and molecules in the upper atmosphere. The excitation energy can be lost by light emission or collisions. Most aurorae are green and red emission from atomic oxygen. Green is a Color, the perception of which is evoked by light having a spectrum dominated by energy with a Wavelength of roughly 520–570- nm. Red is any of a number of similar Colors evoked by light consisting predominantly of the longest wavelengths of Light discernible by the human eye in the wavelength Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Molecular nitrogen and nitrogen ions produce some low level red and very high blue/violet aurorae. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 An ion is an Atom or Molecule which has lost or gained one or more Valence electrons giving it a positive or negative electrical charge Blue is a Colour, the Perception of which is evoked by As the name of a color violet (named after the flower violet) is used in two senses first referring to the color of Light at the short- Wavelength The light blue colors are produced by ionic nitrogen and the neutral nitrogen gives off the red and purple color with the rippled edges. Different gases interacting with the upper atmosphere will produce different colors, caused by the different compounds of oxygen and nitrogen.

Auroral forms and magnetism

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 Earth's magnetic field. Indeed, satellites show electrons to be guided by magnetic field lines, spiraling around them while moving towards Earth.

The curtains often show folds called "striations", which are curtain-like. 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. Perspective, in context of vision and Visual perception, is the way in which objects appear to the Eye based on their spatial attributes or

Although it was first mentioned by Ancient Greek explorer/geographer Pytheas, Hiorter and Celsius first described in 1741 evidence for magnetic control, namely, large magnetic fluctuations occurred whenever the aurora was observed overhead. The Ancient Greek language is the historical stage in the development of the Hellenic language family spanning the Archaic (c A geographer is a Scientist whose area of study is Geography, the study of Earth 's physical environment and Human habitat Dates Pliny says that Timaeus (born about 350 BC believed Pytheas' story of the discovery of Amber. Olof Petrus (Peter Hiorter (1696-1750 was a Swedish Astronomer. Anders Celsius ( November 27, 1701 &ndash April 25, 1744 in Uppsala) was a Swedish astronomer. This indicates (it was later realized) that large electric currents were associated with the aurora, flowing in the region where auroral light originated. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. Kristian Birkeland (1908)^[1] 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). Kristian Olaf Birkeland ( December 13, 1867 - June 15, 1917) was born in Christiania ( Oslo today and wrote his first A Birkeland current is a specific magnetic field aligned current in the Earth’s Magnetosphere which flows from the Magnetotail towards the Earth on the dawn side

Still more evidence for a magnetic connection are the statistics of auroral observations. Elias Loomis (1860) and later in more detail Hermann Fritz (1881)^[2] established that the aurora appeared mainly in the "auroral zone", a ring-shaped region with a radius of approximately 2500 km around Earth's magnetic pole, not its geographic pole. Elias Loomis (August 7 1811 &ndash August 15 1889 was an American Mathematician. It was hardly ever seen near that pole itself. The instantaneous distribution of auroras ("auroral oval", Yasha/Jakob Feldstein 1963^[3]) is slightly different, centered about 3-5 degrees nightward of the magnetic pole, so that auroral arcs reach furthest towards the equator around midnight. The aurora can be seen best at this time.

Solar wind and magnetosphere

The Earth is constantly immersed in the solar wind, a rarefied flow of hot 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 is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. A corona is a type of plasma " atmosphere " of the Sun or other celestial body extending millions of Kilometres into space most easily 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; Earth's surface field is typically 30,000–50,000 nT). The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic 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. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. The Interplanetary Magnetic Field (IMF is the term for the Sun ’s Magnetic field carried by the Solar wind among the Planets of the Solar

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. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming In Physics, magnetism is one of the Phenomena by which Materials exert attractive or repulsive Forces on other Materials. 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. ^[4]

Earth's magnetosphere is the space region dominated by its magnetic field. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. 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). A bow shock is a boundary between a Magnetosphere and an ambient medium 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.

When the solar wind is perturbed, it easily transfers energy and material into the magnetosphere. The electrons and ions in the magnetosphere that are thus energized move along the magnetic field lines to the polar regions of the atmosphere.

Frequency of occurrence

The aurora is a common occurrence in the Poles. 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 eleven-year sunspot cycle or during the three years after that peak. A sunspot is a region on the Sun 's surface ( Photosphere) that is marked by intense magnetic activity which inhibits Convection, forming However, within the auroral zone the likelihood of an aurora occurring depends mostly on the slant of IMF lines (known as B_z, pronounced "bee-sub-zed" or "bee-sub-zee"), being greater with southward slants.

Geomagnetic storms that ignite auroras actually happen more often during the months around the equinoxes. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. An equinox is the event of the Sun passing over the Earth's equator in its annual cycle It is not well understood why geomagnetic storms are tied to Earth's seasons while polar activity is not. But it is known that during spring and autumn, the interplanetary magnetic field and that of Earth link up. At the magnetopause, Earth's magnetic field points north. A magnetopause flows along the boundary between a Magnetic field, (see Magnetosphere) and surrounding plasma. When B_z becomes large and negative (i. e. , the IMF tilts south), it can partially cancel Earth's magnetic field at the point of contact. South-pointing B_z's open a door through which energy from the solar wind can reach Earth's inner magnetosphere.

The peaking of B_z during this time is a result of geometry. The interplanetary magnetic field (IMF) comes from the Sun and is carried outward the solar wind. Because the Sun rotates the IMF has a spiral shape. The Parker spiral is the shape of the Sun 's magnetic field as it extends through the solar system Earth's magnetic dipole axis is most closely aligned with the Parker spiral in April and October. As a result, southward (and northward) excursions of B_z are greatest then.

However, B_z is not the only influence on geomagnetic activity. The Sun's rotation axis is tilted 8 degrees with respect to the plane of Earth's orbit. Because the solar wind blows more rapidly from the Sun's poles than from its equator, the average speed of particles buffeting Earth's magnetosphere waxes and wanes every six months. The solar wind speed is greatest — by about 50 km/s, on average — around September 5 and March 5 when Earth lies at its highest heliographic latitude. Events 1590 - Alexander Farnese 's army forces Henry IV of France to raise the siege of Paris. Events 363 - Roman Emperor Julian moves from Antioch with an army of 90000 to attack the Sassanid Empire, in a

Still, neither B_z nor the solar wind can fully explain the seasonal behavior of geomagnetic storms. Those factors together contribute only about one-third of the observed semiannual variation.

Auroral events of historical significance

The auroras which occurred as a result of the "great geomagnetic storm" on both August 28, 1859 and September 2, 1859 are thought to be perhaps the most spectacular ever witnessed throughout recent recorded history. Events 475 - The Roman General Orestes forces western Roman Emperor Julius Nepos to flee his Capital Year 1859 ( MDCCCLIX) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Balfour Stewart, in a paper ^[5][6] to the Royal Society on November 21, 1861, described both auroral events as documented by a self-recording magnetograph at the Kew Observatory and established the connection between the September 2, 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. Balfour Stewart ( 1 November 1828 &ndash 19 December 1887) was a Scottish physicist The Royal Society of London for the Improvement of Natural Knowledge, known simply as The Royal Society, is a Learned society for science that was founded in 1660 Events 164 BC - Judas Maccabaeus, son of Mattathias of the Hasmonean family restores the Temple in Jerusalem. Year 1861 ( MDCCCLXI) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a Common A magnetograph is one of two types of Scientific instrument: A special type of Magnetometer that records a time plot of the local magnetic field Kew Observatory was an astronomical and terrestrial magnetic Observatory located in Kew, London, England. Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Year 1859 ( MDCCCLIX) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common Richard Christopher Carrington ( May 26 1826 &ndash November 27 1875) was an English amateur Astronomer who discovered ” The second auroral event, which occurred on September 2, 1859 as a result of the exceptionally intense Carrington-Hodgson white light solar flare on September 1, 1859 produced aurora so widespread and extraordinarily brilliant that they were seen and reported in published scientific measurements, ship's logs and newspapers throughout the United States, Europe, Japan and Australia. Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Richard Christopher Carrington ( May 26 1826 &ndash November 27 1875) was an English amateur Astronomer who discovered A solar flare is a violent explosion in a star's (like the Sun 's atmosphere releasing as much Energy as 6 × 1025 Joules Solar flares Events 462 - Possible start of first Byzantine indiction cycle. The United States of America —commonly referred to as the For a topic outline on this subject see List of basic Japan topics. For a topic outline on this subject see List of basic Australia topics. It was reported by the New York Times ^{[7] [8] [9]} that in Boston on Friday September 2, 1859 the Aurora was "so brilliant that at about one o'clock ordinary print could be read by the light"^[8]. Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. Year 1859 ( MDCCCLIX) was a Common year starting on Saturday (link will display the full calendar of the Gregorian calendar (or a Common One o’clock Boston time on Friday September 2, would have been 6:00 GMT and the self-recording magnetograph at the Kew Observatory was recording the geomagnetic storm, which was then one hour old, at its full intensity; this is amazingly accurate news reporting. A magnetograph is one of two types of Scientific instrument: A special type of Magnetometer that records a time plot of the local magnetic field Kew Observatory was an astronomical and terrestrial magnetic Observatory located in Kew, London, England. A geomagnetic storm or solar storm is a temporary disturbance of the Earth 's Magnetosphere caused by a disturbance in Space weather. 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 where he collected world wide reports of the auroral event. Elias Loomis (August 7 1811 &ndash August 15 1889 was an American Mathematician. Elias Loomis (August 7 1811 &ndash August 15 1889 was an American Mathematician. The American Journal of Science ( AJS) is America's longest-running Scientific journal, having been published continuously since its conception in 1818 by Professor The aurora is thought to have been produced by one of the most intense coronal mass ejections in history, very near the maximum intensity that the Sun is thought to be capable of producing. A coronal mass ejection (CME is an ejection of material from the solar Corona, usually observed with a white-light Coronagraph. 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 measurements of the era but also as a result of a significant portion of the 125,000 miles of telegraph lines then in service being significantly disrupted for many hours throughout the storm. A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument Some telegraph lines however, seem to have been of the appropriate length and orientation which allowed a current (geomagnetically induced current) to be induced in them (due to Earth's severely fluctuating magnetosphere) and actually used for communication. Geomagnetically induced currents (GIC affecting the normal operation of long technological conductor systems are a manifestation at ground level of Space weather A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The following conversation occurred between two operators of the American Telegraph Line between Boston and Portland, Maine, on the night of September 2, 1859 and reported in the Boston Traveler:

Boston operator (to Portland operator): "Please cut off your battery [power source] entirely for fifteen minutes. Portland is the largest city in the US state of Maine and the County seat of Cumberland County. Events 44 BC - Pharaoh Cleopatra VII of Egypt declares her son co-ruler as Ptolemy XV Caesarion. "
Portland operator: "Will do so. It is now disconnected. "
Boston: "Mine is disconnected, and we are working with the auroral current. How do you receive my writing?"
Portland: "Better than with our batteries on. - Current comes and goes gradually. "
Boston: "My current is very strong at times, and we can work better without the batteries, as the aurora seems to neutralize and augment our batteries alternately, making current too strong at times for our relay magnets. Suppose we work without batteries while we are affected by this trouble. "
Portland: "Very well. Shall I go ahead with business?"
Boston: "Yes. Go ahead. "

The conversation was carried on for around two hours using no battery 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. ^[10]

Origin

The ultimate energy source of the aurora is the solar wind flowing past the Earth.

magnetosphere and the solar wind consist of plasma (ionized gas), which conducts electricity. In Physics and Chemistry, plasma is an Ionized Gas, in which a certain proportion of Electrons are free rather than being bound It is well known (since Michael Faraday's [1791 - 1867] 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 electrical current is said to be induced into that conductor and electrons will flow within it. Michael Faraday, FRS ( September 22 1791 – August 25 1867) was an English The amount of current flow is dependent upon a) the rate of relative motion and 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 or other fluids. A dynamo, originally another name for an Electrical generator, now means a generator that produces Direct current with the use of a commutator. 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 that plasmas conduct easily along magnetic field lines, but not so easily perpendicular to them. So it is important that a temporary magnetic connection be established between the field lines of the solar wind and those of the magnetosphere, by a process known as magnetic reconnection. Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the 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 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 way 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 exist in the upward extension of the ionosphere, which may extend (with diminishing density) some 25,000 km around Earth. The electron is a fundamental Subatomic particle that was identified and assigned the negative charge in 1897 by J A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The ionosphere is the uppermost part of the atmosphere, distinguished because it is Ionized by solar radiation

Bright auroras are generally associated with Birkeland currents (Schield et al. A Birkeland current is a specific magnetic field aligned current in the Earth’s Magnetosphere which flows from the Magnetotail towards the Earth on the dawn side , 1969;^[11] Zmuda and Armstrong, 1973^[12]) 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. Ohm's law applies to Electrical circuits it states that the current through a conductor between two points is directly proportional to the 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.

Ionospheric resistance has a complex nature, and leads to a secondary Hall current flow. The Hall effect refers to the Potential difference ( Hall voltage) on the opposite sides of an Electrical conductor through which there is an Electric 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.

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^[13]), 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.

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 known as auroral kilometric radiation (AKR, discovered in 1972). 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 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. An Alfvén wave, named after Hannes Alfvén, is a type of magnetohydrodynamic Wave. Hannes Olof Gösta Alfvén ( May 30, 1908; Norrköping, Sweden &ndash April 2, 1995; Djursholm, Sweden 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.

Other processes are also involved in the aurora, and much remains to be learned. Auroral electrons created by large geomagnetic 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.

Sources and types

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 dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a Magnetic field. The circuit of the accelerating currents and their connection to the solar wind are uncertain.
2. Dynamo action involving plasma squeezed towards Earth by sudden convulsions of the magnetotail ("magnetic substorms"). A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. 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. Magnetic flux, represented by the Greek letter Φ ( Phi) is a measure of quantity of Magnetism, taking into account the strength and the extent of a Magnetic 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 towards Earth where their motion feeds large outbursts of aurora, mainly around midnight ("unloading process"). Magnetic reconnection is the process whereby magnetic field lines from different magnetic domains are spliced to one another changing their patterns of connectivity with respect to the A plasmoid is a coherent structure of plasma and Magnetic fields Plasmoids have been proposed to explain natural phenomena such as Ball lightning Geomagnetic 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 Earth's field allows aurora to be visible at middle latitudes, on field lines much closer to the equator.
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". The Van Allen radiation belt is a Torus of energetic Charged particles ( plasma) around Earth, held in place by Earth's Magnetic 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.

The energization of such electrons comes from magnetotail processes. The leakage of negative electrons does not leave the tail positively charged, because each leaked 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 is an expression of the universal law of increasing Entropy, stating that the entropy of an Isolated system which

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. There are other interesting 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.

Magnetic ropes

Scientists have found that an energy source for auroras are giant "Magnetic Ropes" or the energy which comes from a stream of charged particles from the Sun "flowing like a current through twisted bundles of magnetic fields connecting the earth's upper atmosphere to the sun". The Sun (Sol is the Star at the center of the Solar System. The energy is then abruptly released in the form of a shimmering display of lights. ^[14][15]

On other planets

Both Jupiter and Saturn have magnetic fields much stronger than Earth's (in Jupiter it is about 60000 Rayleigh and in Saturn it is between 2000-5000 Rayleigh), and both have large radiation belts. Aurora has been observed on both, most clearly with the Hubble Space Telescope. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into Uranus and Neptune have also been observed to have aurorae. ^[16]

The auroras on the gas giants seem, like Earth's, to be powered by the solar wind. In addition, however, Jupiter's moons, especially Io, are powerful sources of auroras on Jupiter. TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek 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 and an ionosphere, is a particularly strong source, and its currents also generate radio emissions, studied since 1955. Aurorae have also been observed on Io, Europa, and Ganymede themselves, e. TemplateInfobox Planet.--> Io (ˈaɪoʊ, or as Greek g. , using the Hubble Space Telescope. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into These are generated when Jupiter's magnetospheric plasma impact their very thin atmospheres.

Auroras have also been observed on Venus and Mars. Because Venus has no intrinsic (planetary) magnetic field, Venusian aurorae appear as bright and diffuse patches of varying shape and intensity, sometimes distributed across the full planetary disc. Venusian aurorae are produced by the impact of electrons originating from the solar wind and precipitating in the night-side atmosphere. An aurora was also detected on Mars, on August 14, 2004, by the SPICAM instrument aboard Mars Express. Events 1183 - Taira no Munemori and the Taira clan take the young Emperor Antoku and the three sacred treasures "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Mars Express is a Space exploration mission being conducted by the European Space Agency (ESA The aurora was located at Terra Cimmeria, in the region of 177º East, 52º South. Terra Cimmeria is a large Martian region centered at 347S 145E and covering 5400 km at its broadest extent 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. The Mars Global Surveyor ( MGS) was a US Spacecraft developed by NASA and the Jet Propulsion Laboratory and launched This correlation indicates that the origin of the light emission actually was a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars. ^[17][18]

History of Aurora theories

In the past theories have been proposed to explain the phenomenon. These theories are now obsolete.

• Auroral electrons come from beams emitted by the Sun. This was claimed around 1900 by Kristian Birkeland, whose experiments in a vacuum chamber with electron beams and magnetized spheres (miniature models of Earth or "terrellas") showed that such electrons would be guided towards the polar regions. Kristian Olaf Birkeland ( December 13, 1867 - June 15, 1917) was born in Christiania ( Oslo today and wrote his first 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"). The Van Allen radiation belt is a Torus of energetic Charged particles ( plasma) around Earth, held in place by Earth's Magnetic 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. James Alfred Van Allen ( September 7 1914 &ndash August 9, 2006) was an American space scientist at the University of Iowa 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 Earth's field lines to the top of the atmosphere. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. This 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.

Images

Images of aurora are significantly more common today due to the rise of use of digital cameras that have high enough sensitivities. Description and history The Amundsen-Scott South Pole Station is the southernmost continually inhabited place on the planet Many compact digital still cameras can record Sound and moving Video as well as still Photograph. ^[19] Film and digital exposure to auroral displays is fraught with difficulties, particularly if faithfulness of reproduction is an objective. Due to the different spectral energy present, and changing dynamically throughout the exposure, the results are somewhat unpredictable. Different layers of the film emulsion respond differently to lower light levels, and choice of film can be very important. Longer exposures aggregate the rapidly changing energy and often blanket the dynamic attribute of a display. Higher sensitivity creates issues with graininess.

David Malin pioneered multiple exposure using multiple filters for astronomical photography, recombining the images in the laboratory to recreate the visual display more accurately. David Malin (born 28 March 1941) is a British-Australian astronomer and photographer [2] For scientific research, proxies are often used, such as ultra-violet, and re-coloured to simulate the appearance to humans. Predictive techniques are also used, to indicate the extent of the display, a highly useful tool for aurora hunters. [3] Terrestrial features often find their way into aurora images, making them more accessible and more likely to be published by the major websites. ^[20] It is possible to take excellent images with standard film (using ISO ratings between 100 and 400) and a single-lens reflex camera with full aperture, a fast lens (f1. Film speed is the measure of a photographic film's sensitivity to Light. The single-lens reflex (SLR Camera uses an automatic moving mirror system which permits the photographer to see exactly what will be captured by the film or digital imaging 4 50mm, for example), and exposures between 10 and 30 seconds, depending on the aurora's display strength. ^[21]

Early work on the imaging of the Aurora was done in 1949 by the University of Saskatchewan using the SCR-270 radar. The University of Saskatchewan ( U of S) is a Coeducational public Research university located on the east side of the South Saskatchewan SCR-270 ( Signal Corps Radio model 270 was one of the first operational Early warning radars It was the U

In folklore

In Bulfinch's Mythology from 1855 by Thomas Bulfinch there is the claim that in Norse mythology:

The Valkyrior are warlike virgins, mounted upon horses and armed with helmets and spears. Thomas Bulfinch ( July 15 1796 - May 27, 1867) was an American writer born in Newton Massachusetts. Thomas Bulfinch ( July 15 1796 - May 27, 1867) was an American writer born in Newton Massachusetts. Norse mythology comprises the indigenous pre-Christian religion, beliefs and Legends of the Scandinavian peoples including those who settled on Iceland In Norse mythology the valkyries ( Old Norse Valkyrja "Choosers of the Slain" are Dísir, minor female deities /. . . / 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". ^[22]

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 lack of references. Terminology and usage As a cultural term "Scandinavia" has no official definition and is subject to usage by those who identify with the culture in question as well Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( ^[23]

The first Old Norse account of norðurljós is found in the Norwegian chronicle Konungs Skuggsjá from AD 1230. Konungs skuggsjá ( Old Norse for "King's mirror" Latin: Speculum regale, modern Norwegian: Kongsspegelen 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. Greenland (Kalaallit Nunaat meaning "Land of the Greenlanders" Grønland is a self-governing Danish Province located between the "Glacial" and "Glaciation" redirect here For the geological periods see Glacial period. Fluorescence is a Luminescence that is mostly found as an ^[24]

An old Scandinavian name for northern lights translates as "herring flash". Terminology and usage As a cultural term "Scandinavia" has no official definition and is subject to usage by those who identify with the culture in question as well It was believed that northern lights were the reflections cast by large swarms of herring onto the sky. Herring are small Oily fish of the genus Clupea found in the shallow temperate waters of the North Atlantic, the Baltic Sea, the North

Another Scandinavian source refers to "the fires that surround the North and South edges of the world". This has been suggested as evidence that the Norse ventured as far as Antarctica, although this is insufficient to form a conclusion.

The Finnish name for northern lights is revontulet, fox fires. Finnish ( or suomen kieli) is the language spoken by the majority of the population in Finland (92% As of 2006) and by ethnic Finns outside A fox is an Animal belonging to any one of about 27 Species (of which only 12 actually belong to the Vulpes genus or 'true foxes' of small According to legend, foxes made of fire lived in Lapland, and revontulet were the sparks they whisked up into the atmosphere with their tails. The Province of Lapland ( Lappi in Finnish and Sami Lappland in Swedish is one of the Provinces of Finland.

In Estonian they are called virmalised, spirit beings of higher realms. Estonian (; ˈeːsti ˈkeːl is the official language of Estonia, spoken by about 1 In some legends they are given negative characters, in some positive ones.

The Sami people believed that one should be particularly careful and quiet when observed by the northern lights (called guovssahasat in Northern Sami). The Sami people are the Indigenous people of northern Europe inhabiting Sápmi, which today encompasses parts of northern Sweden, Norway Northern or North Sami ( Davvisápmi, formerly Davvisámi or Davvisaami; improperly Lappish or Lapp) is the most widely Mocking the northern lights or singing about them was believed to be particularly dangerous and could cause the lights to descend on the mocker and kill him/her.

The Algonquin believed the lights to be their ancestors dancing around a ceremonial fire. The Algonquins (or Algonkins) are an aboriginal North American people speaking Algonquin, an Anishinaabe language.

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). Latvian language (latviešu valoda is the official state language of Latvia. The soul, according to many religious and philosophical beliefs is the self-awareness, or Consciousness, unique to a particular living An omen (also called portent or presage) is a phenomenon that is believed to foretell the Future, often signifying the advent of change A disaster is the impact of a natural or human-made hazard that negatively affects society or environment. A famine is a widespread shortage of food that may apply to any Faunal species which phenomenon is usually accompanied by regional Malnutrition, Starvation

In Russian folklore aurora borealis was associated with the fire dragon ("Ognenniy Zmey"), who came to women and seduced them in the absence of their husbands. Russian ( transliteration:,) is the most geographically widespread language of Eurasia, the most widely spoken of the Slavic languages The dragon is a Legendary creature of which some interpretation or depiction appears in almost every culture worldwide

In Scotland, the northern lights were known as "the mirrie dancers" or na fir-chlis. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. There are many old sayings about them, including the Scottish Gaelic proverb "When the mirrie dancers play, they are like to slay. A saying is something that is said notable in one respect or another Scottish Gaelic ( Gàidhlig) is a member of the Goidelic branch of Celtic languages. A proverb (from the Latin proverbium) also called a byword or nayword, is a simple and concrete Saying popularly known and repeated " The playfulness of the mirrie 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 among themselves that "the mirrie dancers bled each other last night". Lichens (ˈlaɪkən or /lɪtʃən/ are symbiotic associations of a Fungus (the mycobiont with a photosynthetic partner (the photobiont also known as The appearance of these lights in the sky was considered a sign of the approach of unsettled weather.

Many prospectors during the Klondike Gold Rush believed that the Northern Lights were the reflection of the mother lode of all gold. The Klondike Gold Rush, infrequently referred to as the Yukon Gold Rush or Alaska Gold Rush, was a frenzy of Gold rush Immigration to and for Mother lode is a principal vein or zone of veins of Gold or Silver Ore. Gold (ˈɡoʊld is a Chemical element with the symbol Au (from its Latin name aurum) and Atomic number 79 The most popular poem of the writer Robert W. Service from that era, The Cremation of Sam McGee, begins: "The Northern Lights have seen queer sights, But the queerest they ever did see, Was the night on the marge of Lake Lebarge, I cremated Sam McGee. Robert William Service ( January 16, 1874 &ndash September 11, 1958) was a poet and writer " The Cremation of Sam McGee " is among the most famous of Robert W " In The Ballad of the Northern Lights, Service refers to the theory that the source of the glow is an enormous deposit of radium in the polar region. Radium (ˈreɪdiəm is a radioactive Chemical element which has the symbol Ra and Atomic number 88

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
• Dr. Thomas K. Hatton of the Astronomy Department, University of Chicago
• Eather, Robert H. The University of Chicago is a Private university located principally in the Hyde Park neighborhood of Chicago. (1980). Majestic Lights: The Aurora in Science, History, and The Arts. Washington, DC: American Geophysical Union. ISBN 0-87590-215-4.   (323 pages)
• Syun-Ichi Akasofu (April 2002). "Secrets of the Aurora Borealis". Alaska Geographic Series 29 (1). Graphic Arts Center Publishing Company.  
• Savage, Candace Sherk (1994 / 2001). Aurora: The Mysterious Northern Lights. San Francisco: Sierra Club Books / Firefly Books. ISBN 0-87156-419-X.   (144 pages)
• Phillips, Tony (October 21, 2001). Events 1512 - Martin Luther joins the theological faculty of the University of Wittenberg. Year 2001 ( MMI) was a Common year starting on Monday according to the Gregorian calendar. 'tis the Season for Auroras. NASA. Retrieved on 2006-05-15. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 1252 - Pope Innocent IV issues the Papal bull Ad exstirpanda, which authorizes but also limits the

Footnotes

See also

• Space weather

External links

• NOAA POES Auroral Activity
• Current Solar Data (from NOAA)
• Aurora Forecast (University of Alaska Geophysical Institute)
• Historical
  • Aurora Mythology
  • Aurora in Mythology, theology, history (German)
  • NASA - Carrington Super Flare NASA May 6, 2008
• Aurorology
  • Physics of the Aurora
  • Aurora formation & spectrum
  • Study of Sounds & Acoustical Effects Related to Geomagnetic Storms and Aurora Borealis
  • Frequently asked questions
  • Predicting the Aurora

Space weather is the concept of changing environmental conditions in Outer space. The National Oceanic and Atmospheric Administration ( NOAA) is a scientific agency within the United States Department of Commerce focused on the conditions of the The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Events 1527 - Spanish and German troops sack Rome; some consider this the end of the Renaissance. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common

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