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Aurora

An aurora ( aurorae or auroras), also commonly known as the northern lights (aurora borealis) or southern lights (aurora australis), is a natural light display in Earth's sky, predominantly seen in high-latitude regions (around the Arctic and Antarctic). Auroras display dynamic patterns of brilliant lights that appear as curtains, rays, spirals, or dynamic flickers covering the entire sky.

Auroras are the result of disturbances in the Earth's magnetosphere caused by the solar wind. Major disturbances result from enhancements in the speed of the solar wind from coronal holes and coronal mass ejections. These disturbances alter the trajectories of charged particles in the magnetospheric plasma. These particles, mainly electrons and protons, precipitate into the upper atmosphere (thermosphere/exosphere). The resulting ionization and excitation of atmospheric constituents emit light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles.

Most of the planets in the Solar System, some natural satellites, brown dwarfs, and even comets also host auroras.

Etymology
The term aurora borealis was coined by Galileo in 1619, from the Roman Aurora, goddess of the dawn and the Greek name for the north wind (Boreas). On p. 39, Galileo explains that auroras are due to sunlight reflecting from thin, high clouds. From p. 39: "... molti di voi avranno più d'una volta veduto 'l Cielo nell' ore notturne, nelle parti verso Settentrione, illuminato in modo, che di lucidità non-cede alla piu candida Aurora, ne lontana allo spuntar del Sole; effetto, che per mio credere, non-ha origine altrode, che dall' essersi parte dell' aria vaporosa, che circonda la terra, per qualche cagione in modo più del consueto assottigliata, che sublimandosi assai più del suo consueto, abbia sormontato il cono dell' ombra terrestre, si che essendo la sua parte superiore ferita dal Sole abbia potuto rifletterci il suo splendore, e formarci questa boreale aurora." ("... many of you will have seen, more than once, the sky in the night hours, in parts towards the north, illuminated in a way that the clear [sky] does not yield to the brighter aurora, far from the rising of the sun; an effect that, by my thinking, has no other origin than being part of the vaporous air that surrounds the Earth, for some reason thinner than usual, which, being sublimated far more than expected, has risen above the cone of the Earth's shadow, so that its upper part, being struck by the sun['s light], has been able to reflect its splendor and to form this aurora borealis.")

The word aurora is derived from the name of the Roman goddess of the dawn, Aurora, who travelled from east to west announcing the coming of the Sun. Ancient Greek poets used the corresponding name Eos metaphorically to refer to dawn, often mentioning its play of colors across the otherwise dark sky (e.g., "rosy-fingered dawn").

The words borealis and australis are derived from the names of the ancient gods of the north wind (Boreas) and the south wind (Auster) in Greco-Roman mythology.

Occurrence
Most auroras occur in a band known as the "auroral zone", which is typically 3° to 6° (approximately 330–660 km) wide in latitude and between 10° and 20° from the geomagnetic poles at all local times (or longitudes), most clearly seen at night against a dark sky. A region that currently displays an aurora is called the "auroral oval", a band displaced by the solar wind towards the night side of Earth. Auroras at the North Pole itself are rare due to it being on the Arctic Ocean, while auroras at the South Pole itself are very common and guaranteed to be visible. Early evidence for a geomagnetic connection comes from the statistics of auroral observations. Elias Loomis (1860), and later Hermann Fritz (1881) and Sophus Tromholt (1881) in more detail, established that the aurora appeared mainly in the auroral zone.

In northern latitudes, the effect is known as the aurora borealis or the northern lights. The southern counterpart, the aurora australis or the southern lights, has features almost identical to the aurora borealis and changes simultaneously with changes in the northern auroral zone. The aurora australis is visible from high southern latitudes in Antarctica, the Southern Cone, South Africa, Australasia and under exceptional circumstances as far north as Uruguay. The aurora borealis is visible from areas around the Arctic such as Alaska, Canada, Iceland, Greenland, the Faroe Islands, Scandinavia, Scotland, and Russia. On rare occasions the aurora borealis can be seen as far south as the Mediterranean and the southern states of the US. During the Carrington Event, the greatest geomagnetic storm ever observed, auroras were seen even in the tropics.

A geomagnetic storm causes the auroral ovals (north and south) to expand, bringing the aurora to lower latitudes. The instantaneous distribution of auroras ("auroral oval") is slightly different, being centered about 3–5° nightward of the magnetic pole, so that auroral arcs reach furthest toward the equator when the magnetic pole in question is in between the observer and the Sun. The aurora can be seen best at this time, which is called magnetic midnight.

Auroras seen within the auroral oval may be directly overhead. From farther away, they illuminate the poleward horizon as a greenish glow, or sometimes a faint red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as either diffuse patches or arcs, which can be subvisual.

Auroras are occasionally seen in latitudes below the auroral zone, when a geomagnetic storm temporarily enlarges the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or during the three years after the peak. An electron spirals (gyrates) about a field line at an angle that is determined by its velocity vectors, parallel and perpendicular, respectively, to the local geomagnetic field vector B. This angle is known as the "pitch angle" of the particle. The distance, or radius, of the electron from the field line at any time is known as its Larmor radius. The pitch angle increases as the electron travels to a region of greater field strength nearer to the atmosphere. Thus, it is possible for some particles to return, or mirror, if the angle becomes 90° before entering the atmosphere to collide with the denser molecules there. Other particles that do not mirror enter the atmosphere and contribute to the auroral display over a range of altitudes. Other types of auroras have been observed from space; for example, "poleward arcs" stretching sunward across the polar cap, the related "theta aurora", and "dayside arcs" near noon. These are relatively infrequent and poorly understood. Other interesting effects occur such as pulsating aurora, "black aurora" and their rarer companion "anti-black aurora" and subvisual red arcs. In addition to all these, a weak glow (often deep red) observed around the two polar cusps, the field lines separating the ones that close through Earth from those that are swept into the tail and close remotely.

Images

Early work on the imaging of the auroras was done in 1949 by the University of Saskatchewan using the SCR-270 radar. The altitudes where auroral emissions occur were revealed by Carl Størmer and his colleagues, who used cameras to triangulate more than 12,000 auroras. They discovered that most of the light is produced between 90 and 150 km above the ground, while extending at times to more than 1000 km.

Forms
According to Clark (2007), there are five main forms that can be seen from the ground, from least to most visible:

 * A mild glow, near the horizon. These can be close to the limit of visibility, but can be distinguished from moonlit clouds because stars can be seen undiminished through the glow.
 * Patches or surfaces that look like clouds.
 * Arcs curve across the sky.
 * Rays are light and dark stripes across arcs, reaching upwards by various amounts.
 * Coronas cover much of the sky and diverge from one point on it.

Brekke (1994) also described some auroras as "curtains". The similarity to curtains is often enhanced by folds within the arcs. Arcs can fragment or break up into separate, at times rapidly changing, often rayed features that may fill the whole sky. These are also known as discrete auroras, which are at times bright enough to read a newspaper by at night.

These forms are consistent with auroras being shaped by Earth's magnetic field. The appearances of arcs, rays, curtains, and coronas are determined by the shapes of the luminous parts of the atmosphere and a viewer's position.

Colors and wavelengths of auroral light

 * Red: At its highest altitudes, excited atomic oxygen emits at 630 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low number of oxygen atoms and their gradually diminishing concentration is responsible for the faint appearance of the top parts of the "curtains". Scarlet, crimson, and carmine are the most often-seen hues of red for the auroras.
 * Green: At lower altitudes, the more frequent collisions suppress the 630 nm (red) mode: rather the 557.7 nm emission (green) dominates. A fairly high concentration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to the high stability of the N2 molecule) plays a role here, as it can transfer energy by collision to an oxygen atom, which then radiates it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains. Both the 557.7 and 630.0 nm wavelengths correspond to forbidden transitions of atomic oxygen, a slow mechanism responsible for the graduality (0.7 s and 107 s respectively) of flaring and fading.
 * Blue: At yet lower altitudes, atomic oxygen is uncommon, and molecular nitrogen and ionized molecular nitrogen take over in producing visible light emission, radiating at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the "curtains", show up at the highest levels of solar activity. The molecular nitrogen transitions are much faster than the atomic oxygen ones.
 * Ultraviolet: Ultraviolet radiation from auroras (within the optical window but not visible to virtually all humans) has been observed with the requisite equipment. Ultraviolet auroras have also been seen on Mars, Jupiter, and Saturn.
 * Infrared: Infrared radiation, in wavelengths that are within the optical window, is also part of many auroras.
 * Yellow and pink are a mix of red and green or blue. Other shades of red, as well as orange and gold, may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are linearly independent colors, additive synthesis could, in theory, produce most human-perceived colors, but the ones mentioned in this article comprise a virtually exhaustive list.

Changes with time
Auroras change with time, over the night they begin with glows and progress toward coronas, although they may not reach them. They tend to fade in the opposite order. Until about 1963, it was thought that these changes are due to the rotation of the Earth under a pattern fixed with respect to the Sun. Later, it was found by comparing all-sky films of auroras from different places (collected during the International Geophysical Year) that they often undergo global changes in a process called auroral substorm. They change in a few minutes from quiet arcs all along the auroral oval to active displays along the darkside and after 1 – 3 hours they gradually change back. Changes in auroras over time are commonly visualized using keograms.

At shorter time scales, auroras can change their appearances and intensity, sometimes so slowly as to be difficult to notice, and at other times rapidly down to the sub-second scale. The phenomenon of pulsating auroras is an example of intensity variations over short timescales, typically with periods of 2–20 seconds. This type of aurora is generally accompanied by decreasing peak emission heights of about 8 km for blue and green emissions and above average solar wind speeds (c. 500 km/s).

Other auroral radiation
In addition, the aurora and associated currents produce a strong radio emission around 150 kHz known as auroral kilometric radiation (AKR), discovered in 1972. Ionospheric absorption makes AKR only observable from space. X-ray emissions, originating from the particles associated with auroras, have also been detected.

Noise
Aurora noise, similar to a crackling noise, begins about 70 m above Earth's surface and is caused by charged particles in an inversion layer of the atmosphere formed during a cold night. The charged particles discharge when particles from the Sun hit the inversion layer, creating the noise.

STEVE
In 2016, more than fifty citizen science observations described what was to them an unknown type of aurora which they named "STEVE", for "Strong Thermal Emission Velocity Enhancement". STEVE is not an aurora but is caused by a 25 km wide ribbon of hot plasma at an altitude of 450 km, with a temperature of 3000 C and flowing at a speed of 6 km/s (compared to 10 m/s outside the ribbon).

Picket-fence aurora
The processes that cause STEVE are also associated with a picket-fence aurora, although the latter can be seen without STEVE. It is an aurora because it is caused by precipitation of electrons in the atmosphere but it appears outside the auroral oval, closer to the equator than typical auroras. When the picket-fence aurora appears with STEVE, it is below.

Dune aurora
First reported in 2020 and confirmed in 2021 the dune aurora phenomenon was discovered by Finnish citizen scientists. It consists of regularly-spaced, parallel stripes of brighter emission in the green diffuse aurora which give the impression of sand dunes. The phenomenon is believed to be caused by the modulation of atomic oxygen density by a large-scale atmospheric wave travelling horizontally in a waveguide through an inversion layer in the mesosphere in presence of electron precipitation.

Horse-collar aurora
Horse-collar auroras (HCA) are auroral features in which the auroral ellipse shifts poleward during the dawn and dusk portions and the polar cap becomes teardrop-shaped. They form during periods when the interplanetary magnetic field (IMF) is permanently northward, when the IMF clock angle is small. Their formation is associated with the closure of the magnetic flux at the top of the dayside magnetosphere by the double lobe reconnection (DLR). There are approximately 8 HCA events per month, with no seasonal dependence, and that the IMF must be within 30 degrees of northwards.

Conjugate auroras
Conjugate auroras are nearly exact mirror-image auroras found at conjugate points in the northern and southern hemispheres on the same geomagnetic field lines. These generally happen at the time of the equinoxes, when there is little difference in the orientation of the north and south geomagnetic poles to the sun. Attempts were made to image conjugate auroras by aircraft from Alaska and New Zealand in 1967, 1968, 1970, and 1971, with some success.

Causes
A full understanding of the physical processes which lead to different types of auroras is still incomplete, but the basic cause involves the interaction of the solar wind with Earth's magnetosphere. The varying intensity of the solar wind produces effects of different magnitudes but includes one or more of the following physical scenarios. Aurora australis 20050911.jpg satellite, digitally overlaid onto The Blue Marble composite image.
 * 1) A quiescent solar wind flowing past Earth's magnetosphere steadily interacts with it and can both inject solar wind particles directly onto the geomagnetic field lines that are 'open', as opposed to being 'closed' in the opposite hemisphere and provide diffusion through the bow shock. It can also cause particles already trapped in the radiation belts to precipitate into the atmosphere. Once particles are lost to the atmosphere from the radiation belts, under quiet conditions, new ones replace them only slowly, and the loss-cone becomes depleted. In the magnetotail, however, particle trajectories seem constantly to reshuffle, probably when the particles cross the very weak magnetic field near the equator. As a result, the flow of electrons in that region is nearly the same in all directions ("isotropic") and assures a steady supply of leaking electrons. The leakage of electrons does not leave the tail positively charged, because each leaked electron lost to the atmosphere is replaced by a low energy electron drawn upward from the ionosphere. Such replacement of "hot" electrons by "cold" ones is in complete accord with the second law of thermodynamics. The complete process, which also generates an electric ring current around Earth, is uncertain.
 * 2) Geomagnetic disturbance from an enhanced solar wind causes distortions of the magnetotail ("magnetic substorms"). These 'substorms' tend to occur after prolonged spells (on the order of hours) during which the interplanetary magnetic field has had an appreciable southward component. This leads to a higher rate of interconnection between its field lines and those of Earth. As a result, the solar wind moves magnetic flux (tubes of magnetic field lines, 'locked' together with their resident plasma) from the day side of Earth to the magnetotail, widening the obstacle it presents to the solar wind flow and constricting the tail on the night-side. Ultimately some tail plasma can separate ("magnetic reconnection"); some blobs ("plasmoids") are squeezed downstream and are carried away with the solar wind; others are squeezed toward Earth where their motion feeds strong outbursts of auroras, mainly around midnight ("unloading process"). A geomagnetic storm resulting from greater interaction adds many more particles to the plasma trapped around Earth, also producing enhancement of the "ring current". Occasionally the resulting modification of Earth's magnetic field can be so strong that it produces auroras visible at middle latitudes, on field lines much closer to the equator than those of the auroral zone.
 * Moon and Aurora.jpg and aurora]]
 * 1) Acceleration of auroral charged particles invariably accompanies a magnetospheric disturbance that causes an aurora. This mechanism, which is believed to predominantly arise from strong electric fields along the magnetic field or wave-particle interactions, raises the velocity of a particle in the direction of the guiding magnetic field. The pitch angle is thereby decreased and increases the chance of it being precipitated into the atmosphere. Both electromagnetic and electrostatic waves, produced at the time of greater geomagnetic disturbances, make a significant contribution to the energizing processes that sustain an aurora. Particle acceleration provides a complex intermediate process for transferring energy from the solar wind indirectly into the atmosphere.

An animation created using the same satellite data is also available.]] The details of these phenomena are not fully understood. However, it is clear that the prime source of auroral particles is the solar wind feeding the magnetosphere, the reservoir containing the radiation zones and temporarily magnetically trapped particles confined by the geomagnetic field, coupled with particle acceleration processes.

Auroral particles
The immediate cause of the ionization and excitation of atmospheric constituents leading to auroral emissions was discovered in 1960, when a pioneering rocket flight from Fort Churchill in Canada revealed a flux of electrons entering the atmosphere from above. Since then an extensive collection of measurements has been acquired painstakingly and with steadily improving resolution since the 1960s by many research teams using rockets and satellites to traverse the auroral zone. The main findings have been that auroral arcs and other bright forms are due to electrons that have been accelerated during the final few 10,000 km or so of their plunge into the atmosphere. These electrons often, but not always, exhibit a peak in their energy distribution, and are preferentially aligned along the local direction of the magnetic field.

Electrons mainly responsible for diffuse and pulsating auroras have, in contrast, a smoothly falling energy distribution, and an angular (pitch-angle) distribution favouring directions perpendicular to the local magnetic field. Pulsations were discovered to originate at or close to the equatorial crossing point of auroral zone magnetic field lines. Protons are also associated with auroras, both discrete and diffuse.

Atmosphere
Auroras result from emissions of photons in Earth's upper atmosphere, above 80 km, from ionized nitrogen atoms regaining an electron, and oxygen atoms and nitrogen based molecules returning from an excited state to ground state. They are ionized or excited by the collision of particles precipitated into the atmosphere. Both incoming electrons and protons may be involved. Excitation energy is lost within the atmosphere by the emission of a photon, or by collision with another atom or molecule:
 * Oxygen emissions: green or orange-red, depending on the amount of energy absorbed.
 * Nitrogen emissions:blue, purple or red; blue and purple if the molecule regains an electron after it has been ionized, red if returning to ground state from an excited state.

Oxygen is unusual in terms of its return to ground state: it can take 0.7 seconds to emit the 557.7 nm green light and up to two minutes for the red 630.0 nm emission. Collisions with other atoms or molecules absorb the excitation energy and prevent emission, this process is called collisional quenching. Because the highest parts of the atmosphere contain a higher percentage of oxygen and lower particle densities, such collisions are rare enough to allow time for oxygen to emit red light. Collisions become more frequent progressing down into the atmosphere due to increasing density, so that red emissions do not have time to happen, and eventually, even green light emissions are prevented.

This is why there is a color differential with altitude; at high altitudes oxygen red dominates, then oxygen green and nitrogen blue/purple/red, then finally nitrogen blue/purple/red when collisions prevent oxygen from emitting anything. Green is the most common color. Then comes pink, a mixture of light green and red, followed by pure red, then yellow (a mixture of red and green), and finally, pure blue.

Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes.

Ionosphere
Bright auroras are generally associated with Birkeland currents (Schield et al., 1969; Zmuda and Armstrong, 1973 ), which flow down into the ionosphere on one side of the pole and out on the other. In between, some of the current connects directly through the ionospheric E layer (125 km); the rest ("region 2") detours, leaving again through field lines closer to the equator and closing through the "partial ring current" carried by magnetically trapped plasma. The ionosphere is an ohmic conductor, so some consider that such currents require a driving voltage, which an, as yet unspecified, dynamo mechanism can supply. Electric field probes in orbit above the polar cap suggest voltages of the order of 40,000 volts, rising up to more than 200,000 volts during intense magnetic storms. In another interpretation, the currents are the direct result of electron acceleration into the atmosphere by wave/particle interactions.

Ionospheric resistance has a complex nature, and leads to a secondary Hall current flow. By a strange twist of physics, the magnetic disturbance on the ground due to the main current almost cancels out, so most of the observed effect of auroras is due to a secondary current, the auroral electrojet. An auroral electrojet index (measured in nanotesla) is regularly derived from ground data and serves as a general measure of auroral activity. Kristian Birkeland deduced that the currents flowed in the east–west directions along the auroral arc, and such currents, flowing from the dayside toward (approximately) midnight were later named "auroral electrojets" (see also Birkeland currents). Ionosphere can contribute to the formation of auroral arcs via the feedback instability under high ionospheric resistance conditions, observed at night time and in dark Winter hemisphere.

Interaction of the solar wind with Earth
Earth is constantly immersed in the solar wind, a flow of magnetized hot plasma (a gas of free electrons and positive ions) emitted by the Sun in all directions, a result of the two-million-degree temperature of the Sun's outermost layer, the corona. The solar wind reaches Earth with a velocity typically around 400 km/s, a density of around 5 ions/cm3 and a magnetic field intensity of around 2–5 nT (for comparison, Earth's surface field is typically 30,000–50,000 nT). During magnetic storms, in particular, flows can be several times faster; the interplanetary magnetic field (IMF) may also be much stronger. Joan Feynman deduced in the 1970s that the long-term averages of solar wind speed correlated with geomagnetic activity. Her work resulted from data collected by the Explorer 33 spacecraft.

The solar wind and magnetosphere consist of plasma (ionized gas), which conducts electricity. It is well known (since Michael Faraday's work around 1830) that when an electrical conductor is placed within a magnetic field while relative motion occurs in a direction that the conductor cuts across (or is cut by), rather than along, the lines of the magnetic field, an electric current is induced within the conductor. The strength of the current depends on a) the rate of relative motion, b) the strength of the magnetic field, c) the number of conductors ganged together and d) the distance between the conductor and the magnetic field, while the direction of flow is dependent upon the direction of relative motion. Dynamos make use of this basic process ("the dynamo effect"), any and all conductors, solid or otherwise are so affected, including plasmas and other fluids.

The IMF originates on the Sun, linked to the 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 angles them at Earth by about 45 degrees forming a spiral in the ecliptic plane, known as the Parker spiral. The field lines passing Earth are therefore usually linked to those near the western edge ("limb") of the visible Sun at any time.

The solar wind and the magnetosphere, being two electrically conducting fluids in relative motion, should be able in principle to generate electric currents by dynamo action and impart energy from the flow of the solar wind. However, this process is hampered by the fact that plasmas conduct readily along magnetic field lines, but less readily perpendicular to them. Energy is more effectively transferred by the temporary magnetic connection between the field lines of the solar wind and those of the magnetosphere. Unsurprisingly this process is known as magnetic reconnection. As already mentioned, it happens most readily when the interplanetary field is directed southward, in a similar direction to the geomagnetic field in the inner regions of both the north magnetic pole and south magnetic pole.

Auroras are more frequent and brighter during the intense phase of the solar cycle when coronal mass ejections increase the intensity of the solar wind.

Magnetosphere

Earth's magnetosphere is shaped by the impact of the solar wind on Earth's magnetic field. This forms an obstacle to the flow, diverting it, at an average distance of about 70,000 km (11 Earth radii or Re), producing a bow shock 12,000 km to 15,000 km (1.9 to 2.4 Re) further upstream. The width of the magnetosphere abreast of Earth is typically 190,000 km (30 Re), and on the night side a long "magnetotail" of stretched field lines extends to great distances (> 200 Re).

The high latitude magnetosphere is filled with plasma as the solar wind passes Earth. The flow of plasma into the magnetosphere increases with additional turbulence, density, and speed in the solar wind. This flow is favored by a southward component of the IMF, which can then directly connect to the high latitude geomagnetic field lines. The flow pattern of magnetospheric plasma is mainly from the magnetotail toward Earth, around Earth and back into the solar wind through the magnetopause on the day-side. In addition to moving perpendicular to Earth's magnetic field, some magnetospheric plasma travels down along Earth's magnetic field lines, gains additional energy and loses it to the atmosphere in the auroral zones. The cusps of the magnetosphere, separating geomagnetic field lines that close through Earth from those that close remotely allow a small amount of solar wind to directly reach the top of the atmosphere, producing an auroral glow.

On 26 February 2008, THEMIS probes were able to determine, for the first time, the triggering event for the onset of magnetospheric substorms. Two of the five probes, positioned approximately one third the distance to the Moon, measured events suggesting a magnetic reconnection event 96 seconds prior to auroral intensification.

Geomagnetic storms that ignite auroras may occur more often during the months around the equinoxes. It is not well understood, but geomagnetic storms may vary with Earth's seasons. Two factors to consider are the tilt of both the solar and Earth's axis to the ecliptic plane. As Earth orbits throughout a year, it experiences an interplanetary magnetic field (IMF) from different latitudes of the Sun, which is tilted at 8 degrees. Similarly, the 23-degree tilt of Earth's axis about which the geomagnetic pole rotates with a diurnal variation changes the daily average angle that the geomagnetic field presents to the incident IMF throughout a year. These factors combined can lead to minor cyclical changes in the detailed way that the IMF links to the magnetosphere. In turn, this affects the average probability of opening a door through which energy from the solar wind can reach Earth's inner magnetosphere and thereby enhance auroras. Recent evidence in 2021 has shown that individual separate substorms may in fact be correlated networked communities.

Auroral particle acceleration
Just as there are many types of aurora, there are many different mechanisms that accelerate auroral particles into the atmosphere. Electron aurora in Earth's auroral zone (i.e. commonly visible aurora) can be split into two main categories with different immediate causes: diffuse and discrete aurora. Diffuse aurora appear relatively structureless to an observer on the ground, with indistinct edges and amorphous forms. Discrete aurora are structured into distinct features with well-defined edges such as arcs, rays and coronas; they also tend to be much brighter than the diffuse aurora.

In both cases, the electrons that eventually cause the aurora start out as electrons trapped by the magnetic field in Earth's magnetosphere. These trapped particles bounce back and forth along magnetic field lines and are prevented from hitting the atmosphere by the magnetic mirror formed by the increasing magnetic field strength closer to Earth. The magnetic mirror's ability to trap a particle depends on the particle's pitch angle: the angle between its direction of motion and the local magnetic field. An aurora is created by processes that decrease the pitch angle of many individual electrons, freeing them from the magnetic trap and causing them to hit the atmosphere.

In the case of diffuse auroras, the electron pitch angles are altered by their interaction with various plasma waves. Each interaction is essentially wave-particle scattering; the electron energy after interacting with the wave is similar to its energy before interaction, but the direction of motion is altered. If the final direction of motion after scattering is close to the field line (specifically, if it falls within the loss cone) then the electron will hit the atmosphere. Diffuse auroras are caused by the collective effect of many such scattered electrons hitting the atmosphere. The process is mediated by the plasma waves, which become stronger during periods of high geomagnetic activity, leading to increased diffuse aurora at those times.

In the case of discrete auroras, the trapped electrons are accelerated toward Earth by electric fields that form at an altitude of about 4000–12000 km in the "auroral acceleration region". The electric fields point away from Earth (i.e. upward) along the magnetic field line. Electrons moving downward through these fields gain a substantial amount of energy (on the order of a few keV) in the direction along the magnetic field line toward Earth. This field-aligned acceleration decreases the pitch angle for all of the electrons passing through the region, causing many of them to hit the upper atmosphere. In contrast to the scattering process leading to diffuse auroras, the electric field increases the kinetic energy of all of the electrons transiting downward through the acceleration region by the same amount. This accelerates electrons starting from the magnetosphere with initially low energies (tens of eV or less) to energies required to create an aurora (100s of eV or greater), allowing that large source of particles to contribute to creating auroral light.

The accelerated electrons carry an electric current along the magnetic field lines (a Birkeland current). Since the electric field points in the same direction as the current, there is a net conversion of electromagnetic energy into particle energy in the auroral acceleration region (an electric load). The energy to power this load is eventually supplied by the magnetized solar wind flowing around the obstacle of Earth's magnetic field, although exactly how that power flows through the magnetosphere is still an active area of research. While the energy to power the aurora is ultimately derived from the solar wind, the electrons themselves do not travel directly from the solar wind into Earth's auroral zone; magnetic field lines from these regions do not connect to the solar wind, so there is no direct access for solar wind electrons.

Some auroral features are also created by electrons accelerated by dispersive Alfvén waves. At small wavelengths transverse to the background magnetic field (comparable to the electron inertial length or ion gyroradius), Alfvén waves develop a significant electric field parallel to the background magnetic field. This electric field can accelerate electrons to keV energies, significant to produce auroral arcs. If the electrons have a speed close to that of the wave's phase velocity, they are accelerated in a manner analogous to a surfer catching an ocean wave. This constantly-changing wave electric field can accelerate electrons along the field line, causing some of them to hit the atmosphere. Electrons accelerated by this mechanism tend to have a broad energy spectrum, in contrast to the sharply-peaked energy spectrum typical of electrons accelerated by quasi-static electric fields.

In addition to the discrete and diffuse electron aurora, proton aurora is caused when magnetospheric protons collide with the upper atmosphere. The proton gains an electron in the interaction, and the resulting neutral hydrogen atom emits photons. The resulting light is too dim to be seen with the naked eye. Other aurora not covered by the above discussion include transpolar arcs (formed poleward of the auroral zone), cusp aurora (formed in two small high-latitude areas on the dayside) and some non-terrestrial auroras.

Historically significant events
The discovery of a 1770 Japanese diary in 2017 depicting auroras above the ancient Japanese capital of Kyoto suggested that the storm may have been 7% larger than the Carrington event, which affected telegraph networks.

The auroras that resulted from the Carrington event on both 28 August and 2 September 1859, are thought to be the most spectacular in recent history. In a paper to the Royal Society on 21 November 1861, Balfour Stewart described both auroral events as documented by a self-recording magnetograph at the Kew Observatory and established the connection between the 2 September 1859 auroral storm and the Carrington–Hodgson flare event when he observed that "It is not impossible to suppose that in this case our luminary was taken in the act." The second auroral event, which occurred on 2 September 1859, was a result of the (unseen) coronal mass ejection associated with the exceptionally intense Carrington–Hodgson white light solar flare on 1 September 1859. This event produced auroras so widespread and extraordinarily bright that they were seen and reported in published scientific measurements, ship logs, and newspapers throughout the United States, Europe, Japan, and Australia. It was reported by The New York Times that in Boston on Friday 2 September 1859 the aurora was "so brilliant that at about one o'clock ordinary print could be read by the light". One o'clock EST time on Friday 2 September would have been 6:00 GMT; the self-recording magnetograph at the Kew Observatory was recording the geomagnetic storm, which was then one hour old, at its full intensity. Between 1859 and 1862, Elias Loomis published a series of nine papers on the Great Auroral Exhibition of 1859 in the American Journal of Science where he collected worldwide reports of the auroral event.See:

That aurora is thought to have been produced by one of the most intense coronal mass ejections in history. It is also notable for the fact that it is the first time where the phenomena of auroral activity and electricity were unambiguously linked. This insight was made possible not only due to scientific magnetometer measurements of the era, but also as a result of a significant portion of the 125000 mi of telegraph lines then in service being significantly disrupted for many hours throughout the storm. Some telegraph lines, however, seem to have been of the appropriate length and orientation to produce a sufficient geomagnetically induced current from the electromagnetic field to allow for continued communication with the telegraph operator power supplies switched off. The following conversation occurred between two operators of the American Telegraph Line between Boston and Portland, Maine, on the night of 2 September 1859 and reported in the Boston Traveler:

"Boston operator (to Portland operator): 'Please cut off your battery [power source] entirely for fifteen minutes.'

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. Such events led to the general conclusion that

"The effect of the Aurora on the electric telegraph is generally to increase or diminish the electric current generated in working the wires. Sometimes it entirely neutralizes them, so that, in effect, no fluid [current] is discoverable in them. The aurora borealis seems to be composed of a mass of electric matter, resembling in every respect, that generated by the electric galvanic battery. The currents from it change coming on the wires, and then disappear: the mass of the aurora rolls from the horizon to the zenith."

Historical views and folklore
The earliest datable record of an aurora was recorded in the Bamboo Annals, a historical chronicle of the history of ancient China, in 977 or 957 BC. An aurora was described by the Greek explorer Pytheas in the 4th century BC. Seneca wrote about auroras in the first book of his Naturales Quaestiones, classifying them, for instance, as pithaei ('barrel-like'); chasmata ('chasm'); pogoniae ('bearded'); cyparissae ('like cypress trees'); and describing their manifold colors. He wrote about whether they were above or below the clouds, and recalled that under Tiberius, an aurora formed above the port city of Ostia that was so intense and red that a cohort of the army, stationed nearby for fire duty, galloped to the rescue. It has been suggested that Pliny the Elder depicted the aurora borealis in his Natural History, when he refers to trabes, chasma, 'falling red flames', and 'daylight in the night'.

The earliest depiction of the aurora may have been in Cro-Magnon cave paintings of northern Spain dating to 30,000 BC.

The oldest known written record of the aurora was in a Chinese legend written around 2600 BC. On an autumn around 2000 BC, according to a legend, a young woman named Fubao was sitting alone in the wilderness by a bay, when suddenly a "magical band of light" appeared like "moving clouds and flowing water", turning into a bright halo around the Big Dipper, which cascaded a pale silver brilliance, illuminating the earth and making shapes and shadows seem alive. Moved by this sight, Fubao became pregnant and gave birth to a son, the Emperor Xuanyuan, known legendarily as the initiator of Chinese culture and the ancestor of all Chinese people. In the Shanhaijing, a creature named Shilong is described to be like a red dragon shining in the night sky with a body a thousand miles long. In ancient times, the Chinese did not have a fixed word for the aurora, so it was named according to the different shapes of the aurora, such as "Sky Dog" (天狗), "Sword/Knife Star" (刀星), "Chiyou banner" (蚩尤旗), "Sky's Open Eyes" (天开眼), and "Stars like Rain" (星陨如雨).

In Japanese folklore, pheasants were considered messengers from heaven. However, researchers from Japan's Graduate University for Advanced Studies and National Institute of Polar Research claimed in March 2020 that red pheasant tails witnessed across the night sky over Japan in 620 A.D., might be a red aurora produced during a magnetic storm.

In the traditions of Aboriginal Australians, the Aurora Australis is commonly associated with fire. For example, the Gunditjmara people of western Victoria called auroras puae buae ('ashes'), while the Gunai people of eastern Victoria perceived auroras as bushfires in the spirit world. The Dieri people of South Australia say that an auroral display is kootchee, an evil spirit creating a large fire. Similarly, the Ngarrindjeri people of South Australia refer to auroras seen over Kangaroo Island as the campfires of spirits in the 'Land of the Dead'. Aboriginal people in southwest Queensland believe the auroras to be the fires of the Oola Pikka, ghostly spirits who spoke to the people through auroras. Sacred law forbade anyone except male elders from watching or interpreting the messages of ancestors they believed were transmitted through an aurora.

Among the Māori people of New Zealand, aurora australis or Tahunui-a-rangi ("great torches in the sky") were alight by ancestors who sailed south to a "land of ice" (or their descendants); these people were said to be Ui-te-Rangiora's expedition party who had reached the Southern Ocean. around the 7th century.

In Scandinavia, the first mention of norðrljós (the northern lights) is found in the Norwegian chronicle Konungs Skuggsjá from AD 1230. 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.

Walter William Bryant wrote in his book Kepler (1920) that Tycho Brahe "seems to have been something of a homœopathist, for he recommends sulfur to cure infectious diseases 'brought on by the sulphurous vapours of the Aurora Borealis.

In 1778, Benjamin Franklin theorized in his paper Aurora Borealis, Suppositions and Conjectures towards forming an Hypothesis for its Explanation that an aurora was caused by a concentration of electrical charge in the polar regions intensified by the snow and moisture in the air:

"May not then the great quantity of electricity brought into the polar regions by the clouds, which are condens'd there, and fall in snow, which electricity would enter the earth, but cannot penetrate the ice; may it not, I say (as a bottle overcharged) break thro' that low atmosphere and run along in the vacuum over the air towards the equator, diverging as the degrees of longitude enlarge, strongly visible where densest, and becoming less visible as it more diverges; till it finds a passage to the earth in more temperate climates, or is mingled with the upper air?"

Observations of the rhythmic movement of compass needles due to the influence of an aurora were confirmed in the Swedish city of Uppsala by Anders Celsius and Olof Hiorter. In 1741, Hiorter was able to link large magnetic fluctuations with an aurora being observed overhead. This evidence helped to support their theory that 'magnetic storms' are responsible for such compass fluctuations.

A variety of Native American myths surround the spectacle. The European explorer Samuel Hearne traveled with Chipewyan Dene in 1771 and recorded their views on the ed-thin ('caribou'). According to Hearne, the Dene people saw the resemblance between an aurora and the sparks produced when caribou fur is stroked. They believed that the lights were the spirits of their departed friends dancing in the sky, and when they shone brightly it meant that their deceased friends were very happy.

During the night after the Battle of Fredericksburg, an aurora was seen from the battlefield. The Confederate Army took this as a sign that God was on their side, as the lights were rarely seen so far south. The painting Aurora Borealis by Frederic Edwin Church is widely interpreted to represent the conflict of the American Civil War.

A mid 19th-century British source says auroras were a rare occurrence before the 18th century. It quotes Halley as saying that before the aurora of 1716, no such phenomenon had been recorded for more than 80 years, and none of any consequence since 1574. It says no appearance is recorded in the Transactions of the French Academy of Sciences between 1666 and 1716; and that one aurora recorded in Berlin Miscellany for 1797 was called a very rare event. One observed in 1723 at Bologna was stated to be the first ever seen there. Celsius (1733) states the oldest residents of Uppsala thought the phenomenon a great rarity before 1716. The period between approximately 1645 and 1715 corresponds to the Maunder minimum in sunspot activity.

In Robert W. Service's satirical poem "The Ballad of the Northern Lights" (1908), a Yukon prospector discovers that the aurora is the glow from a radium mine. He stakes his claim, then goes to town looking for investors.

In the early 1900s, the Norwegian scientist Kristian Birkeland laid the foundation for current understanding of geomagnetism and polar auroras.

In Sami mythology, the northern lights are caused by the deceased who bled to death cutting themselves, their blood spilling on the sky. Many aboriginal peoples of northern Eurasia and North America share similar beliefs of northern lights being the blood of the deceased, some believing they are caused by dead warriors' blood spraying on the sky as they engage in playing games, riding horses or having fun in some other way.

Extraterrestrial Aurorae
Saturns Northern Aurora still.jpg.

A movie shows images from 81 hours of observations of Saturn's aurora.]]

Both Jupiter and Saturn have magnetic fields that are stronger than Earth's (Jupiter's equatorial field strength is 4.3 gauss, compared to 0.3 gauss for Earth), and both have extensive radiation belts. Auroras have been observed on both gas planets, most clearly using the Hubble Space Telescope, and the Cassini and Galileo spacecraft, as well as on Uranus and Neptune.

The aurorae on Saturn seem, like Earth's, to be powered by the solar wind. However, Jupiter's aurorae are more complex. Jupiter's main auroral oval is associated with the plasma produced by the volcanic moon Io, and the transport of this plasma within the planet's magnetosphere. An uncertain fraction of Jupiter's aurorae are powered by the solar wind. In addition, the moons, especially Io, are also powerful sources of aurora. These arise from electric currents along field lines ("field aligned currents"), generated by a dynamo mechanism due to the relative motion between the rotating planet and the moving moon. Io, which has active volcanism and an ionosphere, is a particularly strong source, and its currents also generate radio emissions, which have been studied since 1955. Using the Hubble Space Telescope, auroras over Io, Europa and Ganymede have all been observed.

Auroras have also been observed on Venus and Mars. Venus has no magnetic field and so Venusian auroras appear as bright and diffuse patches of varying shape and intensity, sometimes distributed over the full disc of the planet. A Venusian aurora originates when electrons from the solar wind collide with the night-side atmosphere.

An aurora was detected on Mars, on 14 August 2004, by the SPICAM instrument aboard Mars Express. The aurora was located at Terra Cimmeria, in the region of 177° east, 52° south. The total size of the emission region was about 30 km across, and possibly about 8 km high. By analyzing a map of crustal magnetic anomalies compiled with data from Mars Global Surveyor, scientists observed that the region of the emissions corresponded to an area where the strongest magnetic field is localized. This correlation indicated that the origin of the light emission was a flux of electrons moving along the crust magnetic lines and exciting the upper atmosphere of Mars.

Between 2014 and 2016, cometary auroras were observed on comet 67P/Churyumov–Gerasimenko by multiple instruments on the Rosetta spacecraft. The auroras were observed at far-ultraviolet wavelengths. Coma observations revealed atomic emissions of hydrogen and oxygen caused by the photodissociation (not photoionization, like in terrestrial auroras) of water molecules in the comet's coma. The interaction of accelerated electrons from the solar wind with gas particles in the coma is responsible for the aurora. Since comet 67P has no magnetic field, the aurora is diffusely spread around the comet.

Exoplanets, such as hot Jupiters, have been suggested to experience ionization in their upper atmospheres and generate an aurora modified by weather in their turbulent tropospheres. However, there is no current detection of an exoplanet aurora.

The first ever extra-solar auroras were discovered in July 2015 over the brown dwarf star LSR J1835+3259. The mainly red aurora was found to be a million times brighter than the northern lights, a result of the charged particles interacting with hydrogen in the atmosphere. It has been speculated that stellar winds may be stripping off material from the surface of the brown dwarf to produce their own electrons. Another possible explanation for the auroras is that an as-yet-undetected body around the dwarf star is throwing off material, as is the case with Jupiter and its moon Io.

Multimedia

 * Amazing time-lapse video of Aurora Borealis – Shot in Iceland over the winter of 2013/2014
 * Popular video of Aurora Borealis – Taken in Norway in 2011
 * Aurora Photo Gallery – Views taken 2009–2011 (archived 4 October 2011)
 * Aurora Photo Gallery – "Full-Sky Aurora" over Eastern Norway. December 2011
 * Videos and Photos – Auroras at Night (archived 2 September 2010)
 * Video (04:49) – Aurora Borealis – How The Northern Lights Are Created (video on YouTube)
 * Video (47:40) – Northern Lights – Documentary
 * Video (5:00) – Northern lights video in real time
 * Video (01:42) – Northern Light – Story of Geomagnetc Storm (Terschelling Island – 6/7 April 2000) (archived 17 August 2011)
 * Video (01:56) (time-lapse) − Auroras – Ground-Level View from Finnish Lapland 2011 (video on YouTube)
 * Video (02:43) (time-lapse) − Auroras – Ground-Level View from Tromsø, Norway, 24 November 2010 (video on YouTube)
 * Video (00:27) (time-lapse) – Earth and Auroras – Viewed from the International Space Station (video on YouTube)

title: Aurora


text:
Newark

Newark most commonly refers to:

 * Newark, New Jersey, city in the United States
 * Newark Liberty International Airport, New Jersey; a major air hub in the New York metropolitan area

Newark may also refer to:

Canada

 * Niagara-on-the-Lake, Ontario, once called Newark

Germany

 * Neuwerk (Archaic English: Newark), an island and quarter of Hamburg

United Kingdom

 * Newark-on-Trent, Nottinghamshire, England
 * Newark and Sherwood, a local government district
 * Newark (UK Parliament constituency)
 * Newark Wapentake, a former administrative division
 * Newark, Peterborough in Cambridgeshire, a hamlet
 * Port Glasgow, Scotland, called Newark until 1667

United States

 * Newark, Arkansas
 * Newark, California
 * Newark, Delaware
 * Newark, Illinois
 * Newark, Indiana
 * Newark, Maryland
 * Newark, Missouri
 * Newark, Nebraska
 * Newark, New Jersey
 * Newark, New York
 * Newark, Ohio
 * Newark, South Dakota
 * Newark, Texas
 * Newark, Vermont
 * Newark, West Virginia
 * Newark, Wisconsin
 * Newark Islands, Sodus Bay, New York
 * Newark Township (disambiguation)

Other uses

 * Newark (company), American electronic components distribution company
 * HMS Newark, various ships of the Royal Navy
 * USS Newark, various ships of the United States Navy

Other uses

 * Newark Academy (disambiguation)
 * Newark High School (disambiguation)
 * Newark Castle (disambiguation)
 * Newark station (disambiguation)
 * Newark Valley (disambiguation)
 * Roman Catholic Archdiocese of Newark, New Jersey
 * Newark cipher, a variation of the Pigpen cipher system
 * Newark Park, a country house and estate in Gloucestershire, England

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Newark


text:
Stratford

Stratford may refer to:

People

 * Stratford (surname), a list of people with the surname Stratford or de Stratford
 * Stratford (given name), a list of people
 * House of Stratford, a British aristocratic family
 * Tony Banks, Baron Stratford (1942–2006), British politician

Australia

 * Stratford, Queensland, a suburb of Cairns
 * Stratford, Victoria, a town
 * Stratford railway station, Victoria, a railway station
 * Stratford, New South Wales, a town

Canada

 * Stratford, Ontario, a city
 * Stratford station (Ontario), a Via Rail railway station
 * Stratford, Prince Edward Island, a suburb of Charlottetown, the provincial capital
 * Stratford, Quebec, a township

London

 * Stratford, London, a locality of the London borough of Newham
 * Stratford station, a Mainline, London Underground, London Overground, Elizabeth line, National Rail and Docklands Light Railway station
 * Stratford International station, a main line railway and Docklands Light Railway station
 * Stratford High Street DLR station, a Docklands Light Railway station
 * Stratford West Ham (UK Parliament constituency) (1918–1950), East London
 * Stratford (ward), a former electoral ward for Newham London Borough Council from 1964 to 2002
 * Stratford-atte-Bow or Stratford, historical name of Bow, London
 * Stratford Place, a small road in London, off Oxford Street, containing Stratford House

Suffolk

 * Stratford St Andrew, a village and civil parish
 * Stratford St. Mary, a village

Warwickshire

 * Stratford-upon-Avon, a town in Warwickshire, the birth place of William Shakespeare
 * Stratford-on-Avon District, a local government district
 * Stratford-on-Avon (UK Parliament constituency)
 * RAF Stratford, a former Royal Air Force satellite station south of Stratford-upon-Avon

Other counties

 * Stratford Park, an area of Stroud, Gloucestershire
 * Old Stratford, a village in Northamptonshire
 * Stratford-sub-Castle, a suburb of Salisbury, Wiltshire

New Zealand

 * Stratford, New Zealand, a town
 * Stratford (New Zealand electorate), a former parliamentary electorate

United States

 * Stratford, California, a census-designated place
 * Stratford, Connecticut, a town in Fairfield County
 * Stratford station (Connecticut), a Metro-North Railroad station
 * Stratford, Illinois, an unincorporated community
 * Stratford, Iowa, a city
 * Stratford, New Hampshire, a town
 * Stratford, New Jersey, a borough
 * Stratford, New York, a town
 * Stratford, Ohio, an unincorporated community
 * Stratford, Oklahoma, a town
 * Stratford, South Dakota, a town
 * Stratford, Texas, a city
 * Stratford, Washington, an unincorporated community
 * Stratford, Wisconsin, a village
 * Stratford Hall (plantation), a National Register of Historic Places site in Virginia
 * Stratford Shoal, Long Island Sound, Connecticut, site of Stratford Shoal Light, a lighthouse

Other places

 * Stratford-on-Slaney, a village in West Wicklow, Ireland

Schools

 * Stratford University, a higher educational institution with campuses in the United States and India
 * Stratford-upon-Avon College, Stratford-upon-Avon, England, an English further education college
 * Stratford High School (disambiguation)
 * Stratford School (disambiguation)
 * Stratford Girls' Grammar School, Stratford-upon-Avon
 * Stratford College, Dublin, Ireland, a day school
 * Stratford Junior High School, Arlington, Virginia, United States
 * Stratford Academy, Macon, Georgia, United States, a private school

Ships

 * HMCS Stratford, a Second World War Royal Canadian Navy minesweeper
 * Stratford-class transport
 * USS Stratford, a World War II transport ship, one of two in the class
 * HMS Stratford, a fictional ship in the war film Sailor of the King

Sports

 * FC Stratford, a football club based in Stratford-upon-Avon
 * Stratford AFC, association football club based in Stratford, New Zealand
 * Stratford Osceolas, an American professional baseball team located in Stratford, Connecticut, from 1866 to the 1870s
 * Stratford Indians, a former senior ice hockey team based in Stratford, Ontario, Canada
 * Stratford Midgets, a former Canadian junior ice hockey team based in Stratford, Ontario
 * Stratford Nationals, a former semi-professional baseball team based in Stratford, Ontario
 * Stratford Warriors, a junior ice hockey team based in Stratford, Ontario
 * Stratford Professional, a non-ranking snooker tournament staged from 1970 to 1972

Other uses

 * Hotel Stratford, Alton, Illinois, United States, on the National Register of Historic Places
 * Stratford Building, Grand Forks, North Dakota, United States, on the National Register of Historic Places
 * Stratford Press (Cincinnati), a bygone private press

title: Stratford


text:
Groton

Groton may refer to:

England

 * Groton, Suffolk

United States

 * Groton, Connecticut, a town
 * Groton (city), Connecticut, within the town
 * Groton, Massachusetts, a town
 * Groton (CDP), Massachusetts, the main village in the town
 * Groton, New Hampshire
 * Groton Wind Power Project
 * Groton (town), New York
 * Groton (village), New York, within the town
 * Groton, South Dakota
 * Groton, Vermont, a town
 * Groton (CDP), Vermont, within the town

Boarding schools in the United States

 * Groton School
 * Lawrence Academy at Groton

Other

 * Groton Bridge Company, a former American firm
 * Groton High School (disambiguation)

title: Groton


text:
Pirelli

Pirelli & C. S.p.A. is an Italian multinational tyre manufacturer based in the city of Milan, Italy. The company, which has been listed on the Borsa Italiana since 1922, is the 6th-largest tyre manufacturer, and is focused on the consumer production of tyres for cars, motorcycles and bicycles. It is present in Europe, the Asia-Pacific, Latin America, North America, and the post-Soviet states, operating commercially in over 160 countries. It has 19 manufacturing sites, across 13 countries, and a network of around 14,600 distributors and retailers. In 2015, China National Chemical Corp. Ltd. (ChemChina) took controlling interest of Pirelli; with the Chinese state-owned company agreeing to maintain the tyre company's ownership structure until 2023.

Pirelli has been sponsoring sport competitions since 1907 and is the exclusive tyre partner and supplier for the Grand-Am Rolex Sports Car Series for 2008–2010, FIA Formula One World Championship for 2011–present and for the FIM World Superbike Championship. Pirelli's headquarters are located in Milan's Bicocca district. Pirelli is now solely a tyre manufacturing company. In the past, it had been involved in fashion and operated in renewable energy and sustainable mobility.

On 4 October 2017, Pirelli returned to the Milan Stock Exchange after focusing its business on pure consumer products (tyres for car, motorcycles, and bicycles) and related services, and separating the business of industrial tyre. Pirelli's eponymous calendar has been published since 1964, and has featured the contributions of many famous photographers over the years such as Helmut Newton, Steve McCurry, Peter Lindbergh, Richard Avedon, Bruce Weber, Herb Rits, and Annie Leibovitz. The company's US-based headquarters are located in Rome, Georgia.

History
Founded in Milan in 1872 by Giovanni Battista Pirelli (1848–1932), the company initially specialised in rubber and derivative processes and also made scuba diving rebreathers. Thereafter, Pirelli's activities were primarily focused on the production of tyre and cables (for energy and telecommunications). In 2005, Pirelli sold its cable division to Goldman Sachs, which changed the new group's name to Prysmian. In the 1950s, Alberto Pirelli commissioned the building of a skyscraper, Pirelli Tower, in the same Milanese area that housed the very first Pirelli factory during the 19th century.

In 1974, Pirelli invented the "wide radial tyre", upon a request from the Lancia rally racing team for a tyre strong enough to withstand the power of the new Lancia Stratos. At that time, racing tyres were either slick tyres made with the cross ply technique (very wide tyres with a reduced sidewall height), or radial tyres, which were too narrow to withstand the Stratos' power and did not provide enough grip. Both were unusable for the Lancia Stratos, as the radials were destroyed within 10 km, and the slicks too stiff. Lancia asked Pirelli for a solution, and in 1975 Pirelli created a wide tyre with a reduced sidewall height like a slick but with a radial structure. Subsequently, Porsche started using the same tyres with the Porsche 911 Turbo. In 1988, Pirelli acquired the Armstrong Rubber Company, which was headquartered in New Haven, Connecticut, US for $190 million.

In 2000, Pirelli sold its terrestrial fibre optic cables business to Cisco and its optical components operations to Corning, for 5 billion euro. It invested, through Olimpia, part of the resulting liquidity to become a majority shareholder in Telecom Italia in 2001, maintaining this position until 2007. In 2002 the company started a range of Pirelli-branded clothing, watches and eyewear. In 2005, Pirelli sold its Cables, Energy Systems and Telecommunications assets to Goldman Sachs and the newly formed company was named Prysmian. In the same year, 2005, Pirelli opened its first tyre production plant in Shandong province, China. This was the beginning of the group's production complex in the country. In 2006, Pirelli chose Slatina for its first tyre production plant in Romania, expanding the facility in 2011.

In 2010, Pirelli completed its conversion to a pure tyre company by selling Pirelli Broadband Solutions and spinning off the real estate assets of Pirelli Re. Fondazione Pirelli was established in the same year to safeguard and celebrate the company's past and to promote business culture as an integral part of Italy's national cultural assets. In March 2015, it was announced that Pirelli shareholders had accepted a €7.1 billion bid from ChemChina, together with Camfin and LTI, for the company. The transaction was completed and the company was delisted in November 2015. In May 2017, it was announced that Pirelli returns to the world of cycling with a new road cycling tyre range, P ZERO Velo. In September 2017, the company announced its intentions to sell up to 40 per cent of its equity capital in an initial public offering as it plans to return to the Milan stock exchange in October. In March 2019 Pirelli announced a new range of mountain biking tyres, called Scorpion. In 2021, Pirelli introduced 18-inch tyres for the new aerodynamic and technical changes for 2022 in Formula One. As of May 2024, Pirelli has a market capitalisation of $6.69 billion. On May 29, 2024 Silk Road Fund began the total sale of its shareholding. On May 30, 2024, the share price fell as a result of the sale of the entire stake of Silk Road Fund. While Tronchetti Provera's Camfin strengthened its shareholding together with other Italian investors.

Business areas

 * Pirelli is focused on the consumer business, producing tyres for cars, motorcycles, and bicycles.

Car products range

 * P ZERO: Tyres for ultra-high performance cars. P ZERO branding is used for dry weather Formula One tyres, along with other racing tyres.
 * Cinturato: Tyres for high-end cars. Cinturato branding is used for wet-weather Formula One tyres.
 * Sottozero: Winter tyres for high-end cars. Sottozero branding is used for WRC tyres.
 * Carrier: Tyres for vans.
 * Ice: Tyres designed for extremely low temperatures.
 * Scorpion: Tyres for SUV and cross-over.

Moto products range

 * Diablo: Road and track tyres.
 * Angel: Street and commuting tyres.
 * Scorpion: Road and off-road tyres.

Velo products range

 * P ZERO Velo: Road racing.
 * Cycl-e: Urban and electric.
 * Scorpion: Mountain bike.
 * Cinturato: Gravel.

Major shareholders
Pirelli shareholders as of December 2022:

Board of directors
The list of Pirelli Board of Directors:

Marketing
The Pirelli Calendar is published annually, featuring actresses and fashion models. The calendar also features the work of fashion photographers, including Richard Avedon, Peter Lindbergh, Annie Leibovitz, and Patrick Demarchelier. The Pirelli Internetional Award is given annually for the best international multimedia involving the communication of science and technology conducted entirely on the Internet. "Power is nothing without control" was the well-known slogan of Pirelli Tyre Company, and was featured in numerous television and print advertisements. Pirelli is the long-serving main sponsor of Italian football club Inter Milan, having sponsored the Italian team since the 1995–96 season.

Football
Pirelli has a history of sponsoring football teams. Pirelli is well known for its long-term primary sponsorship of the Italian football club Inter Milan between 1995 and 2021. Pirelli previously appeared as a sponsor on the shirts of the Maltese football club Valletta for a short time. In reference to Brazil striker Ronaldo’s usual goal celebration of both arms outstretched, Pirelli ran a 1998 commercial in which he replaced the figure of Christ from the Christ the Redeemer statue that towers over his home city of Rio de Janeiro while in an Inter Milan strip. It was controversial with the Catholic Church.

Pirelli's sponsorship of football teams is not limited to Europe, South America is a key market and as a result, successful clubs have also been sponsored by the tyre company. The Brazilian team Palmeiras, Uruguayan team Peñarol and Argentinian side Vélez Sársfield all had Pirelli as a shirt sponsor. When English football club Burton Albion Football Club built their new stadium in 2005, Pirelli became the title sponsor of the new ground. This was because the new stadium, named Pirelli Stadium lies next to the Pirelli factory in Burton-upon-Trent, Staffordshire, England. In 2009, Pirelli became the title sponsor of the Chinese Super League (CSL), China's top-tier football league. In 2012, the company became a major sponsor of the Russian Cup.

Motorsport
Pirelli is the event title sponsor of the Spanish and Hungarian Grands Prix and sponsored the 2018 French Grand Prix. The company was the title sponsor of the Pirelli World Challenge from 2011 to 2018. Pirelli supported rally with their FIA Pirelli Star Driver program as an initiative to support young rally drivers. It was the sole supplier in the top tier of World Rally Championship in 2008–2010, and is now a co-supplier with Michelin. Since its first involvement in WRC in 1973, the manufacturer won 181 events, and produced 25 WRC Driver Champions including Colin McRae (1995), Petter Solberg (2003), Sebastien Loeb (2008–2010). Pirelli would again become the sole tyre supplier in all three tiers in 2021. Pirelli has also been a sponsor of rally and gymkhana driver Ken Block's Hoonigan Racing Division since 2010.

America's Cup
Pirelli was sponsor of Emirates Team New Zealand in the 35th America's Cup (2017).

Winter Sports
Pirelli sponsored Alpine World Ski Championship and Ice Hockey World Championship IIHF from 2017 to 2021. The company is also sponsor of the Italian Ski Team and of the Swiss Ski Team.

Baseball
Pirelli also was a sponsor of the Los Angeles Dodgers of Major League Baseball from 2014 to 2020.

Motorsport
Pirelli was the official tyre partner and supplier of the World Rally Championship from 2008 to 2010 until the company withdrew to focus on its Formula One commitments. Pirelli returned to the championship in 2014, albeit only partnering tyres for a few private teams as Michelin was the major tyre partner and supplier. Pirelli stepped up their involvement in the championship when they signed a deal to supply tyres to all Junior WRC participants, with its champions receiving a Ford Fiesta R5 with free tyres, fuel and free rally registration package for the next season's World Rally Championship-2. Pirelli subsequently returned full time to the WRC since 2021 season. Pirelli was also partnered Grand-Am Rolex Sports Car Series from 2008 until 2010 before being replaced by Continental AG in 2011. The company has been the official supplier of the GT World Challenge America since 2011 and the GT World Challenge Europe Endurance Cup since 2013.

Formula One
Pirelli has been the sole tyre supplier in Formula One since 2011 following Bridgestone's decision to withdraw from the role at the end of 2010. Pirelli previously competed in Formula One from 1950–1958, 1981–1986 and 1989–1991. Pirelli also supplies tyres for the FIA Formula 2 Championship (formerly GP2 Series), FIA Formula 3 Championship (formerly GP3 Series) and F1 Academy, that form the feeder series to Formula One. Pirelli's deal is due to end after the 2027 Formula One World Championship.

The Italian tyre manufacturer introduced a colour coding system to help identify the tyre compounds used by drivers during races. Each compound has its own colour, which appears on the sidewalls of the tyre. Since the 2019 season, Pirelli has used three colours to identify its dry-weather P Zero tyres: white for hard, yellow for medium, and red for soft. As well as the dry-weather slick tyres, there are two wet-weather grooved tyres: green for the intermediate and blue for the full wet. These tyres are branded Cinturato, a name that dates back to the 1950s. At the start of Pirelli's Formula One tenure in 2011, the company was given the technically challenging task of designing tyres that degraded rapidly in order to promote more pit stops and overtaking, with the aim of making the races more exciting and entertaining. However, the brief from the sport's organisers has changed over the years, as the cars themselves evolved with the introduction of the turbo hybrid era in 2014.

Pirelli has faced controversy on a number of occasions in Formula One, especially during the 2013 British Grand Prix, which featured multiple tyre failures. Pirelli subsequently changed the construction of the tyres to prevent further incidents, switching to Kevlar belts. At the 2015 Belgian Grand Prix, a tyre on Sebastian Vettel's Ferrari suffered from a blowout at 200 mph. Immediately after the race Pirelli claimed that excessive wear caused the blowout but following a more detailed analysis, the company said that in fact, a cut had caused the tyre failure. A number of major changes to the Formula One tyres were introduced for the 2017 season. The most obvious visual difference was an increase of width by 25%, both front and rear, increasing from 245-mm to 305-mm at the front and 325-mm to 405-mm at the rear. The actual rim size remained unchanged from the traditional 13 inches. The faster cornering speeds as a result of this change imposed significantly increased loads on the tyres. Pirelli was consequently asked to produce tyres with less degradation that were more resistant to overheating, for the fastest cars in Formula One history.

A far-reaching alteration to the Formula One technical regulations for 2022, covering every aspect of the car, prompted another significant change to the tyres. With an imminent move to 18-inch rims after more than 50 years of the 13-inch size, Pirelli's 2022 tyres maintain the same tread width as before, but diameter has increased from 660 millimetres to 720 millimetres. The sidewall height is also reduced to give the tyres a more modern low-profile look.

Superbike World Championship
Pirelli is the only allowed tyre brand in the FIM Superbike World Championship since 2007 (along with its support classes, such as the Supersport World Championship). Pirelli has also been awarded the contract for the control tyre supply in the British Superbike Championship from 2008 until at least 2010.

Grand Prix motorcycle racing
Pirelli officially replaces Dunlop as the sole tire supplier for Moto3 and Moto2 starting in 2024. This was announced by Dorna Sports via the official MotoGP website. The Pirelli and Dorna contract has a duration of three seasons.

Overseas investment
In April 2012, Pirelli & C. SpA signed a joint venture agreement with Indonesian counterpart PT Astra Autoparts a subsidiary of PT Astra International for the construction of a motorcycle tyre plant with a total investment of $120 million. 60 per cent of shares will be held by Pirelli. Pirelli hoped to strengthen its presence in the largest motorcycle market in the world, Southeast Asia which has 250 million motorcycles.

Audio system
In July 2018, Pirelli launched a Formula One wheel-shaped Bluetooth speaker, P Zero Sound. The Bluetooth speaker measures 12.9 in in diameter, weighs 21 lb and has a 100-watt amplifier, a 100 mm mid-woofer, a 25 mm tweeter and also offers Bluetooth 4.0 with AptX for wireless connectivity. IXOOST is the manufacturer of P Zero Sound speaker, which majorly manufactures Motorsports-themed audio systems. The wheel-shaped speaker costs €2400, which is equivalent to about $2,800.

title: Pirelli


text:
No contest (disambiguation)

No contest, or nolo contendere, is a plea in a criminal court case.

No contest may also refer to:

 * No contest (combat sports), a match that ends without a winner or loser
 * No Contest (film) a film starring Shannon Tweed

title: No contest (disambiguation)


text:
Sequoia

Sequoia, Sequoya or Sequoyah refers to a type of tree in the cypress family which includes the redwood trees. By extension the name may refer to:

Biology

 * Sequoioideae, a three-genus subfamily of the cypress family
 * Sequoia (genus), a genus with one living and several fossil species
 * Sequoia sempervirens, coast redwood, found along the coast of California and Oregon
 * Sequoiadendron giganteum (giant sequoia), the sequoia tree found on the slopes of the Sierra Nevada of California
 * Metasequoia, dawn redwood
 * The Great Sequoia, a sequoia tree in Vitoria-Gasteiz, Basque Country, Spain

Other science and technology

 * macOS Sequoia, an operating system version
 * 1103 Sequoia, a minor planet
 * Sequoia (supercomputer), an IBM supercomputer at Lawrence Livermore National Laboratory, US
 * HFS Plus, a file system codenamed Sequoia

Arts and entertainment

 * Old Sequoia, a 1945 American animated short film directed by Jack King
 * Sequoia (1934 film), an American drama film
 * Sequoia (2014 film), an American comedy film
 * Sequoia (comics), a Marvel Comics character
 * Sequoia (composition), by American composer Joan Tower
 * "Sequoia", a song by Way Out West from Way Out West
 * Sequoya (Ream), a bronze sculpture
 * Sequoya (St. John's University's Literary Magazine)

United States

 * State of Sequoyah, an attempt in the early 20th century by Native Americans to form their own state
 * Canyon, California, formerly Sequoya
 * Mount Sequoyah, Great Smoky Mountains
 * Sequoia Hall, home of the Statistics Department of Stanford University
 * Sequoia Hospital, Redwood City, California
 * Sequoia National Park, a national park in the southern Sierra Nevada, California
 * Sequoia National Forest, adjacent to the Sequoia National Park
 * Giant Sequoia National Monument, monument administered as part of the National Forest
 * Sequoia Park Zoo, in Eureka, California
 * Sequoyah County, Oklahoma, a county in mid-eastern Oklahoma bordering Arkansas
 * Sequoyah Nuclear Plant, Tennessee
 * Sequoyah, Oklahoma, an unincorporated community in northeastern Oklahoma

Elsewhere

 * Tour Sequoia, an office skyscraper in Paris, France

Schools

 * Sequoia Middle School (disambiguation), several schools
 * Sequoia High School (disambiguation), several schools
 * Sequoyah High School (Georgia), public school in Canton, Georgia
 * Sequoyah High School (Claremore, Oklahoma), public school
 * Sequoyah High School (Tahlequah, Oklahoma), high school and Native American boarding school
 * Sequoyah School, a non-profit, independent alternative school in Pasadena, California
 * Sequoia University, a defunct Los Angeles diploma mill

Companies

 * Sequoia Capital, a venture capital firm
 * Sequoia Voting Systems, a California company that provides electronic voting systems
 * Sequoia Fund, a Ruane, Cunniff & Goldfarb investment fund

Transport

 * Piper Sequoya, a variant of the Piper Aerostar, a light twin-engine utility aircraft
 * Sequoia Falco, a light, acrobatic aircraft
 * Sequoia Field Airport, near Visalia, California, US
 * Toyota Sequoia, a sport utility vehicle
 * USS Sequoia, several US Navy ships
 * USS Sequoia (presidential yacht), U.S. presidential yacht
 * USS Sequoyah (SP-426), a patrol boat in commission from 1917 to 1919

People

 * Sequoyah (1767–1843), American Indian silversmith and inventor of the Cherokee syllabary
 * Johnny Sequoyah (born 2002), American actress
 * Sequoia Holmes, American basketball player
 * Sequoia Nagamatsu, American writer and professor
 * Billy Ray Waldon, also known as Nvwtohiyada Idehesdi Sequoyah (born 1952), American former fugitive, American Indian Movement activist, and Esperantist

Other uses

 * Sequoyah (horse), Irish Thoroughbred racehorse
 * Secoya (disambiguation)

title: Sequoia


text:
Redwood (disambiguation)

Redwood is a common name for Sequoioideae, a subfamily of coniferous trees.

Redwood or Redwood Tree may also refer to:

Arts and entertainment

 * The Redwoods, a 1967 short documentary film
 * Redwood (band), English alternative rock
 * Three Dog Night, American rock band known as Redwood (1967–1968)
 * Redwood (album), by Lúnasa, 2003
 * "Redwood Tree" (song), by Van Morrison, 1972
 * "Redwoods", a 2012 song by Scale the Summit

Businesses

 * Redwood Games, an American creator of educational video games
 * Redwood Group, now ESR Group, a real estate services and investment company
 * Redwood Library and Athenaeum, in Newport, Rhode Island, U.S.
 * Redwood Materials, an American company

Education

 * Redwood High School (disambiguation)
 * Redwood Middle School (disambiguation)
 * College of the Redwoods, Eureka, California, U.S.

People

 * Redwood baronets, a title in the Baronetage of the United Kingdom
 * Bernard Boverton Redwood (1874–1911), British motorboat racer
 * Thomas Boverton Redwood (1846–1919), British chemical engineer
 * Abraham Redwood (1709–1788), West Indies merchant, slave trader and philanthropist
 * Charlie Redwood (1878–1954), Australian rugby union player
 * Doug Redwood (1918–after 1939), Welsh professional footballer
 * Francis Redwood (1839–1935), Roman Catholic Archbishop of Wellington
 * Frederick Redwood (born 1964), Jamaican cricketer
 * George Redwood (1885–1956), English footballer
 * Henry Redwood (1823–1907) New Zealand farmer, politician and racehorse breeder
 * Hubert Redwood (1913–1943), English professional footballer
 * John Redwood (born 1951), British politician
 * Stanley Redwood (born 1965), Jamaican minister and former politician
 * Theophilus Redwood (1806–1892), Welsh pharmacist
 * Vernon Redwood (1873–1954), Australian maltster and politician
 * Zahra Redwood (born c. 1985), Miss Jamaica Universe 2007

United States

 * Redwood City, California
 * Redwood City station
 * Redwood National and State Parks, including Redwood National Park, California
 * Redwood Village, San Diego, California
 * Redwood (Bar Harbor, Maine), a historic house
 * Redwood County, Minnesota
 * Redwood Falls, Minnesota
 * Redwood Falls Township, Redwood County, Minnesota
 * Redwood, Mississippi
 * Redwood, New York
 * Redwood, Oregon
 * Redwood, Texas
 * Redwood, Virginia
 * Redwood River, a tributary of the Minnesota River

Other countries

 * Redwood, Queensland, Australia
 * Redwood, Ontario, Canada
 * Redwood, Ottawa, Canada
 * Redwood, County Tipperary, Ireland
 * Redwood Castle
 * Redwood, Christchurch, New Zealand
 * Redwood, Wellington, New Zealand
 * Redwood railway station

Other uses

 * Eucalyptus transcontinentalis, commonly known as redwood
 * Redwoods Lacrosse Club in the Premier Lacrosse League
 * Redwood, the callsign for Virgin America
 * Redwood, in TeraScale (microarchitecture)
 * USS Redwood, an American net laying ship

title: Redwood (disambiguation)


text:
Aurora (aircraft)

Aurora is a rumored mid-1980s American reconnaissance aircraft. There is no substantial evidence that it was ever built or flown and it has been termed a myth.

The U.S. government has consistently denied such an aircraft was ever built. Aviation and space reference site Aerospaceweb.org concluded, "The evidence supporting the Aurora is circumstantial or pure conjecture, there is little reason to contradict the government's position."

Former Skunk Works director Ben Rich confirmed that "Aurora" was simply a myth in Skunk Works (1994), a book detailing his days as the director. Rich wrote that a colonel working in the Pentagon arbitrarily assigned the name "Aurora" to the funding for the B-2 bomber design competition and somehow the name was leaked to the media.

In 2006, veteran black project watcher and aviation writer Bill Sweetman said, "Does Aurora exist? Years of pursuit have led me to believe that, yes, Aurora is most likely in active development, spurred on by recent advances that have allowed technology to catch up with the ambition that launched the program a generation ago."

Background
The Aurora legend started in 1985, when the Los Angeles Times and later Aviation Week & Space Technology magazine broke the news that the term "Aurora" had been inadvertently included in the 1985 U.S. budget, as an allocation of $455 million for "black aircraft production" in FY 1987. According to Aviation Week, Project Aurora referred to a group of exotic aircraft, and not to one particular airframe. Funding of the project allegedly reached $2.3 billion in fiscal 1987, according to a 1986 procurement document obtained by Aviation Week. In the 1994 book Skunk Works, Ben Rich, the former head of Lockheed's Skunk Works division, wrote that the Aurora was the budgetary code name for the stealth bomber fly-off that resulted in the B-2 Spirit.

Evidence
By the late 1980s, many aerospace industry observers believed that the U.S. had the technological capability to build a Mach 5 (hypersonic speed) replacement for the aging Lockheed SR-71 Blackbird. Detailed examinations of the U.S. defense budget claimed to have found money missing or channeled into black projects. By the mid-1990s, reports surfaced of sightings of unidentified aircraft flying over California and the United Kingdom involving odd-shaped contrails, sonic booms, and related phenomena that suggested the US had developed such an aircraft. Nothing ever linked any of these observations to any program or aircraft type, but the name Aurora was often tagged on these as a way of explaining the observations.

British sighting claims
In late August 1989, while working as an engineer on the jack-up barge GSF Galveston Key in the North Sea, Chris Gibson saw an unfamiliar isosceles triangle-shaped delta aircraft, apparently refueling from a Boeing KC-135 Stratotanker and accompanied by a pair of F-111 fighter-bombers. Gibson watched the aircraft for several minutes, until they went out of sight. He subsequently drew a sketch of the formation. When the sighting was made public in 1992, the British Defence Secretary Tom King was told, "There is no knowledge in the MoD of a 'black' programme of this nature, although it would not surprise the relevant desk officers in the Air Staff and Defence Intelligence Staff if it did exist."

Group Captain Tom Eeles, RAF, writes of a mystery aircraft flying over his house, near to the Mildenhall USAF base in Suffolk, at about 2:00am on a Sunday morning in the autumn of 1993. He had been awoken by "a very strange-sounding aircraft passing overhead; the engine noise was a pulsing sound quite unlike anything I'd heard before." He saw lights disappearing towards Mildenhall. Enquiries were made of a senior RAF officer at Mildenhall the following morning, at which point he was told firmly "to stop making inquiries at once". Group Captain Eeles attributes this sighting to a new stealth aircraft called Aurora. A few weeks earlier, there had been "an unexplained incident at Boscombe Down apparently involving an emergency landing by an unknown US aircraft, after which it was covered in tarpaulins and removed with great secrecy by an American C5 transport aircraft."

A crash at RAF Boscombe Down in Wiltshire on 26 September 1994 appeared closely linked to "black" missions, according to a report in AirForces Monthly. Further investigation was hampered by USAF aircraft flooding into the base. Special Air Service personnel arrived in plainclothes in an Agusta 109. The crash site was protected from view by fire engines and tarpaulins and the base was closed to all flights soon afterwards. More recent analysis, however, indicates that the Boscombe Down crash was a towed missile decoy.

An unsubstantiated claim on the Horsted Keynes Village Web Site purports to show photos of the trail left after an unusual sonic boom was heard over the village in July 2002. In 2005 the information was used in a BBC report about the Aurora project.

U.S. sighting claims
A series of unusual sonic booms was detected in Southern California beginning in mid-to-late 1991 and recorded by United States Geological Survey sensors across Southern California used to pinpoint earthquake epicenters. The sonic booms were characteristic of a smaller vehicle, rather than of the 37-meter long Space Shuttle orbiter. Furthermore, neither the Shuttle nor NASA's single SR-71B was operating on the days the booms had been registered. In the article, "In Plane Sight?" which appeared in the Washington City Paper on 3 July 1992 (pp. 12–13), one of the seismologists, Jim Mori, noted: "We can't tell anything about the vehicle. They seem stronger than other sonic booms that we record once in a while. They've all come on Thursday mornings about the same time, between 4 and 7." Former NASA sonic boom expert Dom Maglieri studied the 15-year-old sonic boom data from the California Institute of Technology and has deemed that the data showed "something at 90,000 ft (c. 27 km), Mach 4 to Mach 5.2". He also said the booms did not look like those from aircraft that had traveled through the atmosphere many miles away at Los Angeles International Airport; rather, they appeared to be booms from a high-altitude aircraft directly above the ground, moving at high speeds. The boom signatures of the two different aircraft patterns are wildly different. There was nothing particular to tie these events to any aircraft, but they served to increase the number of stories about the Aurora. On 23 March 1992, near Amarillo, Texas, Steven Douglass photographed the "donuts on a rope" contrail and linked this sighting to distinctive sounds. He described the engine noise as: "strange, loud pulsating roar... unique... a deep pulsating rumble that vibrated the house and made the windows shake... similar to rocket engine noise, but deeper, with evenly timed pulses." In addition to providing the first photographs of the distinctive contrail previously reported by many, the significance of this sighting was enhanced by Douglass' reports of intercepts of radio transmissions: "Air-to-air communications... were between an AWACS aircraft with the call sign "Dragnet 51" from Tinker AFB, Oklahoma, and two unknown aircraft using the call signs "Darkstar November" and "Darkstar Mike". Messages consisted of phonetically transmitted alphanumerics. It is not known whether this radio traffic had any association with the "pulser" that had just flown over Amarillo." ("Darkstar" is also a call sign of AWACS aircraft from a different squadron at Tinker AFB) A month later, radio enthusiasts in California monitoring Edwards AFB Radar (callsign "Joshua Control") heard early morning radio transmissions between Joshua and a high flying aircraft using the callsign "Gaspipe". "You're at 67,000 feet, 81 miles out" was heard, followed by "70 miles out now, 36,000 ft, above glideslope." As in the past, nothing linked these observations to any particular aircraft or program, but the attribution to the Aurora helped expand the legend.

In February 1994, a former resident of Rachel, Nevada, and Area 51 enthusiast, Chuck Clark, claimed to have filmed the Aurora taking off from the Groom Lake facility. In the David Darlington book Area 51: The Dreamland Chronicles, he said:

"I even saw the Aurora take off one night–or an aircraft that matched the Aurora's reputed configuration: a sharp delta with twin tails about a hundred and thirty feet long. It taxied out of a lighted hangar at 2:30a.m. and used a lot of runway to take off. It had one red light on top, but the minute the wheels left the runway, the light went off and that was the last I saw of it. I didn't hear it because the wind was blowing from behind me toward the base.' I asked when this had taken place. 'February 1994. Obviously they didn't think anybody was out there. It was thirty below zero – probably ninety below with the wind chill factor. I had hiked into White Sides from a different, harder way than usual, and stayed there two or three days among the rocks, under a camouflage tarp with six layers of clothes on. I had an insulated face mask and two sleeping bags, so I didn't present a heat signature. I videotaped the aircraft through a telescope with a five-hundred-millimeter f4 lens coupled via a C-ring to a high-eight digital video camera with five hundred and twenty scan lines of resolution, which is better than TV.' The author then asked, 'Where's the tape?' 'Locked away. That's a legitimate spyplane; my purpose is not to give away legitimate national defense. When they get ready to unveil it, I'll probably release the tape.'"

Additional claims
By 1996, reports associated with the Aurora name dropped off in frequency, suggesting to people who believed that the aircraft existed that it had only ever been a prototype or that it had had a short service life.

In 2000, Aberdeen Press and Journal writer Nic Outterside wrote a piece on US stealth technology in Scotland. Citing confidential "sources", he alleged RAF/USAF Machrihanish in Kintyre, Argyll to be a base for Aurora aircraft. Machrihanish's almost 2 mi long runway makes it suitable for high-altitude and experimental aircraft with the fenced-off coastal approach making it ideal for takeoffs and landings to be made well away from eyes or cameras of press and public. "Oceanic Air Traffic Control at Prestwick," Outterside says, "also tracked fast-moving radar blips. It was claimed by staff that a 'hypersonic jet was the only rational conclusion' for the readings."

In 2006, aviation writer Bill Sweetman put together 20 years of examining budget "holes", unexplained sonic booms, as well as the Gibson sighting and concluded:

"This evidence helps establish the program's initial existence. My investigations continue to turn up evidence that suggests current activity. For example, having spent years sifting through military budgets, tracking untraceable dollars and code names, I learned how to sort out where money was going. This year, when I looked at the Air Force operations budget in detail, I found a $9-billion black hole that seems a perfect fit for a project like Aurora."

In June 2017, Aviation Week reported that Rob Weiss, the General Manager of the Skunk Works, provided some confirmation of a research project and stated that hypersonic flight technology was now mature, and efforts were underway to fly an aircraft with it.

title: Aurora (aircraft)


text:
Groom Lake (salt flat)

Groom Lake is a dry lake, also described as a salt flat, in Nevada. It is used for runways of the Nellis Bombing Range Test Site airport (KXTA). Part of the Area 51 USAF installation, it lies at an elevation of 4409 ft and is approximately 3.7 mi from north to south and 3 mi from east to west at its widest point, and is approximately 11.3 miles in circumference. Located within the namesake Groom Lake Valley portion of the Tonopah Basin, the lake is 25 mi south of Rachel, Nevada.

The nearest publicly accessible vantage point is Tikaboo Peak, 26 miles to the east. There were two closer vantage points, dubbed "Freedom Ridge" and "White Sides", but they were closed to public access in 1995 to prevent people from taking pictures of the installation.

History
Lead and silver were discovered in the southern part of the Groom Range in 1864, and the English Groome Lead Mines Limited company financed the Conception Mines in the 1870s, giving the district its name (nearby mines included Maria, Willow and White Lake). The mining claims in Groom were acquired by J. B. Osborne and partners and patented in 1876, and Osborne's son acquired the interests in the 1890s. The claims were proved in 1916 when two companies began working their mines; that work continued until 1918, and resuming after World War II until the early 1950s.

In popular culture
In the Call of Duty: Black Ops franchise's Zombies mode, Groom Lake appears repeatedly as a test site for the American government's experiments with lunar teleportation.

title: Groom Lake (salt flat)