An aurora (plural: aurorae or auroras) is a natural light show in Earth's upper atmosphere. It happens when charged particles from the Sun collide with atoms in the atmosphere. These collisions make oxygen and nitrogen glow, creating light in colors like green, red, and purple. In high-latitude areas, auroras are called polar lights or aurora polaris. In the Arctic, they are known as the northern lights or aurora borealis. In the Antarctic, they are called the southern lights or aurora australis. Auroras appear as moving patterns of light in the sky, such as curtains, rays, spirals, or flickers.

Auroras occur when the Earth's magnetosphere is disturbed by fast-moving solar wind from areas on the Sun called coronal holes and explosions called coronal mass ejections. These disturbances change the paths of charged particles in the magnetosphere. These particles, mostly electrons and protons, fall into the upper atmosphere (thermosphere/exosphere). This causes ionization and glowing of atmospheric gases, producing light of different colors and patterns. The shape of auroras, which appear in bands near the poles, depends on how much energy is given to the particles falling into the atmosphere.

Other planets in the Solar System, brown dwarfs, comets, and some moons also have auroras.

Etymology

The term aurora borealis was first used in a 1649 description by Pierre Gassendi, who wrote about an auroral display seen across France in 1621. Gassendi had read the writings of Galileo Galilei, who used the term in his many writings about auroras in 1619. The term was added to the English language in 1828.

The word "aurora" comes from the name of the Roman goddess of dawn, Aurora, who was said to travel from east to west to signal the arrival of the sun. The word "aurora" was first used in English in the 14th century. The words "borealis" and "australis" are taken from the names of ancient Greek gods: Boreas, the god of the north wind, and Auster, the god of the south wind.

Modern style guides suggest that the names of weather-related events, such as aurora borealis, should not be capitalized. In the United States, the plural form "auroras" is now more commonly used, but "aurorae" is the original Latin plural and is often used by scientists. In some cases, "aurora" is treated as an uncountable noun, and multiple sightings may be referred to as "the aurora."

Characterisation

Auroras are most often seen in the "auroral zone," a band about 6° wide in latitude centered around 67° north and south. The area currently showing an aurora is called the "auroral oval." The oval moves due to the solar wind, shifting it about 15° away from the geomagnetic pole (not the geographic pole) toward noon and 23° away toward midnight. The oval’s farthest point toward the equator is slightly shifted from geographic midnight. It is centered about 3–5° nightward of the magnetic pole so that auroral arcs reach farthest toward the equator when the magnetic pole is between the observer and the Sun, known as magnetic midnight.

Early evidence linking auroras to Earth’s magnetic field comes from statistical studies of auroral sightings. Elias Loomis (1860) and later Hermann Fritz (1881) and Sophus Tromholt (1881) found that auroras mostly appear in the auroral zone.

In northern latitudes, this phenomenon is called the aurora borealis or northern lights. The southern version, the aurora australis or southern lights, has nearly identical features and changes at the same time as the northern aurora. The southern lights are visible from high southern latitudes, including Antarctica, Patagonia, southeastern Australia, New Zealand, and the Falkland Islands. The northern lights are visible near the Arctic, such as in Alaska, Canada, Iceland, Greenland, the Faroe Islands, Scandinavia, Finland, Scotland, and Russia. A geomagnetic storm causes the auroral ovals (north and south) to expand, making the aurora visible at lower latitudes or higher in the south. On rare occasions, the northern lights can be seen as far south as the Mediterranean, East Asia, and the southern United States, while the southern lights can be seen as far north as New Caledonia, South Africa, the Pilbara region in Western Australia, and Uruguay. During the Carrington Event, the largest geomagnetic storm ever recorded, auroras were seen even in the tropics.

Auroras within the auroral oval may appear directly overhead. From farther away, they glow greenish or faintly red, as if the Sun were rising from an unusual direction. Auroras also occur poleward of the auroral zone as diffuse patches or arcs, which may be hard to see.

Auroras are sometimes seen below the auroral zone during geomagnetic storms, which temporarily enlarge the auroral oval. Large geomagnetic storms are most common during the peak of the 11-year sunspot cycle or the three years after the peak. An electron moves around a magnetic field line at an angle determined by its velocity, which is called the "pitch angle." The distance of the electron from the field line is called the "Larmor radius." As the electron moves to regions with stronger magnetic fields near Earth’s atmosphere, its pitch angle increases. If the angle reaches 90°, the electron may return, or "mirror," before entering the atmosphere. Other electrons enter the atmosphere and create auroras at different altitudes. Other auroras observed from space include "poleward arcs," "theta auroras," and "dayside arcs." These are rare and not fully understood. Other effects include pulsating auroras, "black auroras," "anti-black auroras," and subvisual red arcs. A weak red glow is also seen around Earth’s polar cusps, the magnetic field lines that separate those closing through Earth from those in the tail that close remotely.

Starting in 1911, Carl Størmer and colleagues used cameras to study over 12,000 auroras. They found no auroras below 70 km (43 mi) and only 6.5% above 150 km (93 mi), with most auroras appearing around 100 km (62 mi).

According to Clark (2007), five main types of auroras can be seen from Earth, from least to most visible:

Brekke (1994) also described some auroras as "curtains." The shape of arcs can resemble curtains, especially when folded. Arcs may break into separate, rapidly changing features that fill the sky. These are called "discrete auroras" and can be bright enough to read a newspaper at night.

These forms match how Earth’s magnetic field shapes auroras. The appearance of arcs, rays, curtains, and coronas depends on the glowing parts of the atmosphere and the viewer’s position.

Auroras change over time. At night, they often start as glows and progress to coronas, though they may not reach that stage. They fade in the opposite order. Until about 1963, scientists thought these changes were caused by Earth’s rotation under a fixed pattern related to the Sun. Later, by comparing aurora films from different locations during the International Geophysical Year, scientists found that auroras undergo global changes in a process called an "auroral substorm." These changes occur in minutes, shifting from quiet arcs to active displays on the dark side of Earth, then gradually returning to normal after 1–3 hours. Changes in auroras over time are often visualized using "keograms."

At shorter time scales, auroras can change slowly or rapidly, even down to sub-second intervals. Pulsating auroras are an example of rapid intensity changes, typically lasting 2–20 seconds. These auroras are often linked to lower-than-usual emission heights for blue and green light and faster-than-average solar wind speeds (about 500 km/s).

Auroras and related currents also produce strong radio emissions at 150 kHz, called "auroral kilometric radiation" (AKR), discovered in 1972. Ionospheric absorption limits AKR to observation from space. X-ray emissions from aurora-related particles have also been detected.

A crackling noise, heard about 70 m (230 ft) above Earth’s surface, is caused by charged particles in an inversion layer of the atmosphere formed during cold nights. When solar particles hit this layer, they discharge, creating the sound.

In 2016, over 50 citizen science reports described an unknown aurora they named "STEVE," short for "Strong Thermal Emission Velocity Enhancement." STEVE is not an aurora but caused by a 25 km (16 mi) wide ribbon of hot plasma at 450 km (280 mi) altitude, with a temperature of 3,000°C (3,270 K; 5,430°F) and flowing at 6 km/s (3.7 mi/s),

Causes

A full understanding of the physical processes that create different types of auroras is still incomplete. However, the basic cause involves the interaction between the solar wind and Earth's magnetosphere. The changing strength of the solar wind causes effects of different sizes, which include one or more of the following physical situations.

The details of these phenomena are not fully understood. However, it is clear that the main source of auroral particles is the solar wind, which supplies the magnetosphere. The magnetosphere acts as a storage area for radiation zones and temporarily holds particles trapped by Earth's magnetic field. These particles are also accelerated by specific processes.

In 1960, scientists discovered that electrons from above the atmosphere cause ionization and excitation of atmospheric gases, leading to auroral emissions. Since then, many research teams have collected detailed measurements using rockets and satellites to study the auroral zone. Key findings show that auroral arcs and bright forms are caused by electrons that gain speed during their final journey into the atmosphere. These electrons often have a peak in their energy levels and move mostly along the direction of Earth's magnetic field.

Electrons are mainly responsible for diffuse and pulsating auroras. These auroras have a smooth decrease in energy levels and move more in directions perpendicular to the magnetic field. Pulsations are found near the equatorial crossing point of magnetic field lines in the auroral zone. Protons are also linked to both discrete and diffuse auroras.

Auroras occur when photons are emitted from Earth's upper atmosphere, above 80 km (50 mi). This happens when ionized nitrogen atoms regain electrons, and oxygen atoms and nitrogen-based molecules return to their normal state after being excited. These processes are caused by collisions with particles falling into the atmosphere. Both electrons and protons can be involved. Excitation energy is released as light or absorbed through collisions with other atoms or molecules.

Oxygen behaves differently compared to other elements. It can take up to 0.7 seconds to emit green light at 557.7 nm and up to two minutes to emit red light at 630.0 nm. Collisions with other atoms or molecules absorb energy and stop emissions, a process called collisional quenching. At high altitudes, where oxygen is more common and particle density is lower, collisions are rare, allowing oxygen to emit red light. As altitude decreases and particle density increases, collisions become more frequent, preventing red and green light emissions.

The change in auroral color with altitude is explained by this process. Oxygen red light is most common at high altitudes, followed by oxygen green light and nitrogen blue, purple, or red light. At lower altitudes, nitrogen colors dominate due to frequent collisions that block oxygen emissions. Green is the most common color, followed by pink (a mix of green and red), pure red, yellow (a mix of red and green), and finally, pure blue.

Protons that fall into the atmosphere often become hydrogen atoms after gaining electrons from the air. Proton auroras are usually seen at lower latitudes.

Bright auroras are often linked to Birkeland currents, which flow into the ionosphere on one side of a pole and out on the other. Some of these currents pass through the ionospheric E layer (125 km), while others detour through field lines closer to the equator and connect to the "partial ring current." The ionosphere acts like a resistor, and some scientists believe a voltage from an unknown dynamo mechanism drives these currents. Measurements suggest voltages of about 40,000 volts, rising to over 200,000 volts during strong magnetic storms. Another view is that these currents result from electrons being accelerated by wave-particle interactions.

Ionospheric resistance causes a secondary Hall current. The magnetic disturbance on Earth's surface caused by the main current is mostly canceled out, so most auroral effects are due to a secondary current called the auroral electrojet. An auroral electrojet index, measured in nanotesla, is regularly calculated from ground data and reflects auroral activity. Kristian Birkeland found that these currents flow east-west along auroral arcs and were later named "auroral electrojets." The ionosphere can contribute to auroral arcs through feedback instability under high resistance conditions, observed at night and in the dark winter hemisphere.

Interaction of the solar wind with Earth

Earth is always surrounded by the solar wind, a stream of magnetized hot plasma (a gas made of free electrons and positive ions) that flows outward from the Sun in all directions. This flow happens because the Sun’s outermost layer, called the corona, reaches temperatures of about two million degrees. The solar wind reaches Earth at speeds of about 400 kilometers per second, with a density of about 5 ions per cubic centimeter, and a magnetic field strength of about 2 to 5 nanoteslas (nT). For comparison, Earth’s magnetic field at the surface is usually 30,000 to 50,000 nT. During magnetic storms, the solar wind can move much faster, and the interplanetary magnetic field (IMF) may become stronger. In the 1970s, Joan Feynman discovered that the average speed of the solar wind over long periods is related to geomagnetic activity. Her findings were based on data collected by the Explorer 33 spacecraft.

The solar wind and Earth’s magnetosphere are made of plasma, which conducts electricity. As Michael Faraday showed in the 1830s, when an electrical conductor moves through a magnetic field in a direction that crosses the field lines, an electric current is created in the conductor. The strength of this current depends on the speed of movement, the strength of the magnetic field, the number of conductors, and the distance between the conductor and the field. The direction of the current depends on the direction of movement. This process, called the dynamo effect, is used in dynamos and affects all conductors, including plasmas and other fluids.

The IMF originates on the Sun and is connected to sunspots. Its magnetic field lines are pulled outward by the solar wind. This would normally align the field lines in the direction between the Sun and Earth, but the Sun’s rotation causes them to angle about 45 degrees at Earth, forming a spiral in the ecliptic plane known as the Parker spiral. The field lines that reach Earth are usually linked to those near the western edge of the visible Sun.

The solar wind and magnetosphere are two electrically conducting fluids moving relative to each other. In theory, this movement could create electric currents through the dynamo effect, transferring energy from the solar wind. However, plasmas conduct electricity more easily along magnetic field lines than across them. Energy is more efficiently transferred through temporary magnetic connections between the solar wind’s field lines and those of the magnetosphere. This process, called magnetic reconnection, happens most often when the IMF is directed southward, matching the direction of Earth’s magnetic field near the north and south magnetic poles.

Auroras are more common and brighter during the intense phase of the solar cycle, when coronal mass ejections increase the strength of the solar wind.

Earth’s magnetosphere is shaped by the solar wind’s impact on Earth’s magnetic field. This creates a barrier that diverts the solar wind, forming an obstacle about 70,000 kilometers (11 Earth radii) from Earth. A bow shock forms 12,000 to 15,000 kilometers (1.9 to 2.4 Earth radii) further upstream. The magnetosphere is about 190,000 kilometers (30 Earth radii) wide near Earth and has a long, stretched "magnetotail" extending far beyond Earth on the night side.

The high-latitude region of the magnetosphere contains plasma from the solar wind. More plasma flows into the magnetosphere when the solar wind is more turbulent, dense, or fast. This flow is encouraged by a southward component of the IMF, which connects directly to Earth’s magnetic field lines at high latitudes. Plasma in the magnetosphere generally moves from the magnetotail toward Earth, around Earth, and back into the solar wind through the magnetopause on the day side. Some plasma also moves along Earth’s magnetic field lines, gains energy, and releases it into the atmosphere in the auroral zones. The cusps of the magnetosphere, which separate magnetic field lines that loop through Earth from those that extend into space, allow a small amount of solar wind to reach Earth’s atmosphere, creating auroras.

On February 26, 2008, the THEMIS probes identified, for the first time, the event that starts magnetospheric substorms. Two of the five probes, located about one-third the distance to the Moon, measured signs of a magnetic reconnection event 96 seconds before auroras intensified.

Geomagnetic storms that cause auroras may occur more frequently around the equinoxes. It is not fully understood why, but geomagnetic storms may vary with Earth’s seasons. Two factors to consider are the tilt of the Sun’s axis and Earth’s axis relative to the ecliptic plane. As Earth orbits the Sun, it encounters the IMF from different latitudes on the Sun, which is tilted by 8 degrees. Earth’s 23-degree axial tilt also changes the angle at which Earth’s magnetic field meets the IMF throughout the year. These factors may cause small, regular changes in how the IMF connects to the magnetosphere, affecting how much energy from the solar wind reaches Earth’s inner magnetosphere and enhances auroras. Recent evidence from 2021 suggests that individual substorms may be linked in networks.

Auroral particle acceleration

There are many types of auroras, and each type is caused by different processes that speed up particles in Earth's atmosphere. In Earth's auroral zone, where auroras are commonly seen, electron auroras can be divided into two main groups: diffuse and discrete auroras. Diffuse auroras look blurry and have unclear edges to someone on the ground. Discrete auroras have clear shapes, such as arcs, rays, and coronas, and are usually brighter than diffuse auroras.

In both cases, the electrons that cause auroras start as particles trapped by Earth's magnetic field in the magnetosphere. These trapped electrons move back and forth along magnetic field lines and are kept from entering the atmosphere by a magnetic mirror that forms near Earth. The magnetic mirror's ability to trap a particle depends on the particle's pitch angle—the angle between its path and the magnetic field. Auroras occur when processes change the pitch angles of many electrons, allowing them to escape the magnetic trap and enter the atmosphere.

For diffuse auroras, the pitch angles of electrons change when they interact with plasma waves. These interactions scatter the electrons, altering their direction but not their energy. If the final direction of motion is close to the magnetic field line (within the loss cone), the electrons will enter the atmosphere. Diffuse auroras happen when many scattered electrons hit the atmosphere at the same time. This process is influenced by plasma waves, which become stronger during times of high geomagnetic activity, causing more diffuse auroras.

For discrete auroras, electrons are accelerated toward Earth by electric fields in the auroral acceleration region, located about 4000–12000 km above Earth. These electric fields point upward along the magnetic field line. Electrons moving downward through these fields gain energy, reducing their pitch angles and allowing them to enter the atmosphere. Unlike the scattering process that causes diffuse auroras, the electric fields increase the energy of all electrons passing through the region equally. This energy boost allows electrons with low initial energy to reach the high energy needed to create auroras.

The accelerated electrons carry an electric current along the magnetic field lines (a Birkeland current). Since the electric field and current move in the same direction, energy from electromagnetic waves is converted into particle energy in the auroral acceleration region. This energy comes from the solar wind, which flows around Earth's magnetic field. However, the exact path of this energy through the magnetosphere is still being studied. Although the energy for auroras comes from the solar wind, the electrons themselves do not travel directly from the solar wind to Earth's auroral zone. Magnetic field lines in these regions do not connect to the solar wind, so solar wind electrons cannot reach the auroral zone directly.

Some auroral features are caused by electrons accelerated by dispersive Alfvén waves. At small wavelengths, these waves create a strong electric field parallel to the magnetic field. This electric field can accelerate electrons to high enough energies to produce auroral arcs. If electrons move at a speed close to the wave's phase velocity, they are accelerated like a surfer catching a wave. This changing electric field can push electrons along the magnetic field line, causing some to enter the atmosphere. Electrons accelerated by this method have a wide range of energy levels, unlike those accelerated by static electric fields, which have a narrow energy range.

In addition to diffuse and discrete auroras, proton auroras occur when magnetospheric protons collide with the upper atmosphere. During this collision, protons gain an electron, forming neutral hydrogen atoms that emit light. However, this light is too dim to see with the naked eye. Other auroras not covered here include transpolar arcs (found poleward of the auroral zone), cusp auroras (found in two small high-latitude areas on the dayside), and auroras on other planets.

Historically significant events

In 2017, scientists found a diary from 1770 in Japan that showed auroras above Kyoto. This suggests the storm might have been 7% stronger than the Carrington Event, which disrupted telegraph systems.

The auroras caused by the Carrington Event on August 28 and September 2, 1859, were the most spectacular in recent history. In 1861, Balfour Stewart wrote a paper for the Royal Society describing auroras recorded by a self-recording magnetograph at Kew Observatory. He linked the September 2 aurora to the Carrington–Hodgson flare event, noting that "It is not impossible to suppose that in this case our luminary was taken in the act." The September 2 aurora resulted from a coronal mass ejection tied to the intense Carrington–Hodgson solar flare on September 1, 1859. This event produced auroras visible in the United States, Europe, Japan, and Australia. The New York Times reported that in Boston on September 2, 1859, the aurora was "so brilliant that ordinary print could be read by its light" at 1:00 AM EST (6:00 GMT). At that time, the Kew Observatory magnetograph was recording the geomagnetic storm at its peak intensity. Between 1859 and 1862, Elias Loomis published nine papers in the American Journal of Science collecting global reports of the 1859 auroral event.

This aurora is believed to have been caused by one of the most intense coronal mass ejections in history. It was the first time auroral activity and electricity were clearly connected. Scientists used magnetometer data and noted that telegraph lines were disrupted for many hours. Some telegraph lines, however, allowed communication without batteries due to geomagnetically induced currents. On September 2, 1859, operators on the American Telegraph Line between Boston and Portland, Maine, reported:

Boston operator: "Please cut off your battery 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. 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 lasted about two hours without battery power, using only the aurora-induced current. This was the first recorded instance of more than a few words being transmitted in this way. Scientists later concluded that auroras can increase or decrease electric currents in telegraph lines. Sometimes, auroras cancel out the current entirely. The aurora borealis appears to consist of electric matter similar to that from batteries, and its currents change as they travel along wires.

In May 2024, solar storms caused the aurora borealis to be seen as far south as Ferdows, Iran.

Historical views and folklore

The earliest known record of an aurora is found in the Bamboo Annals, a historical document from ancient China, which dates the event to 977 or 957 BC. The Greek explorer Pytheas described an aurora in the 4th century BC. Seneca, a Roman writer, wrote about auroras in his book Naturales Quaestiones. He gave names to different shapes, such as pithaei ("barrel-like"), chasmata ("chasm"), pogoniae ("bearded"), and cyparissae ("like cypress trees"). He also noted their colors and whether they appeared above or below the clouds. Seneca wrote that during the time of Emperor Tiberius, a bright red aurora was seen above the port city of Ostia. This caused a group of soldiers stationed nearby to ride to the city, thinking a fire had started. Some scholars believe that Pliny the Elder described the aurora borealis in his book Natural History, using terms like trabes, chasma, "falling red flames," and "daylight in the night."

The oldest known image of an aurora may be in cave paintings from northern Spain, created about 30,000 BC. The first written record of a wintertime aurora appears in a Chinese legend from around 2600 BC. A record of an autumn aurora is found in writings from about 2000 BC.

In Japanese folklore, pheasants were believed to be messengers from heaven. However, in 2020, researchers from Japan suggested that "red pheasant tails" seen in the night sky over Japan in 620 AD might have actually been a red aurora caused by a magnetic storm.

Among Aboriginal Australians, the aurora australis is often linked to fire. The Gunditjmara people of western Victoria called auroras puae buae ("ashes"), while the Gunai people of eastern Victoria saw auroras as bushfires in the spirit world. The Dieri people of South Australia referred to auroras as kootchee, meaning an evil spirit creating a large fire. The Ngarrindjeri people of South Australia believed auroras over Kangaroo Island were the campfires of spirits in the "Land of the Dead." In southwest Queensland, the Dieri and Ngarrindjeri communities saw auroras as the fires of the Oola Pikka, ghostly spirits who communicated through auroras. Sacred laws in these communities forbade anyone except male elders from watching or interpreting auroras, as they were thought to carry messages from ancestors.

The Māori people of New Zealand called the aurora australis Tahunui-a-rangi ("great torches in the sky"). They believed these lights were created by ancestors who sailed south to a "land of ice" or by their descendants. These ancestors were said to be part of the expedition led by Ui-te-Rangiora, who reached the Southern Ocean around the 7th century.

In Scandinavia, the first written mention of norðrljós (the northern lights) appears in the Norwegian chronicle Konungs Skuggsjá from 1230 AD. The writer learned about the phenomenon from people returning from Greenland and gave three possible explanations: that the ocean was surrounded by fires, that the sun’s energy could reach Earth’s night side, or that glaciers stored energy that later became visible as light.

In 1920, Walter William Bryant wrote in his book Kepler that Tycho Brahe, a scientist, suggested using sulfur to treat diseases caused by "sulphurous vapours of the Aurora Borealis."

In 1778, Benjamin Franklin proposed in his paper Aurora Borealis, Suppositions and Conjectures that auroras might be caused by a buildup of electricity in polar regions. He theorized that electricity from clouds condensed in the snow might enter the ground but not the ice, causing it to escape into the atmosphere and travel toward the equator.

In 1741, scientists Anders Celsius and Olof Hiorter in Sweden observed that compass needles moved rhythmically during auroras. Hiorter linked this to magnetic fluctuations, supporting the idea that "magnetic storms" caused these changes.

Many Native American cultures have myths about auroras. In 1771, European explorer Samuel Hearne recorded that the Chipewyan Dene people saw auroras as sparks from caribou fur and believed they were the spirits of their dead friends dancing in the sky. They thought bright auroras meant their deceased friends were happy.

After the Battle of Fredericksburg during the American Civil War, an aurora was seen from the battlefield. The Confederate Army believed this was a sign that God supported them, as auroras were rarely seen so far south. The painting Aurora Borealis by Frederic Edwin Church is often interpreted as a representation of the American Civil War.

A mid-19th-century British source noted that auroras were rare before the 18th century. It cited Halley’s observation that no major auroras were recorded for over 80 years before 1716 and none since 1574. No auroras were noted in the Transactions of the French Academy of Sciences between 1666 and 1716. A rare aurora in 1797 was recorded in Berlin Miscellany, and one in 1723 at Bologna was called the first ever seen there. Celsius (1733) wrote that people in Uppsala believed auroras were very rare before 1716. This period, from about 1645 to 1715, matches the Maunder minimum, a time of low sunspot activity.

In his 1908 satirical poem The Ballad of the Northern Lights, Robert W. Service wrote about a Yukon prospector who mistakenly believed the aurora was the glow from a radium mine.

In the early 1900s, Norwegian scientist Kristian Birkeland developed a theory that helped explain how auroras form and how Earth’s magnetic field interacts with space.

In Sami mythology, the northern lights are believed to be the blood of the dead spilling into the sky. Many indigenous groups in northern Eurasia and North America share similar beliefs, seeing

Extraterrestrial auroras

Auroras have been seen on all planets that have magnetic fields except Neptune. The process that creates auroras is the same everywhere, but the results can vary.

Jupiter and Saturn both have magnetic fields stronger than Earth's. Jupiter's magnetic field at its equator is 4.3 gauss, compared to Earth's 0.3 gauss. Both planets also have large radiation belts. Auroras have been observed on Jupiter and Saturn, most clearly through the Hubble Space Telescope and spacecraft like Cassini and Galileo. Auroras have also been seen on Uranus and Neptune.

On Saturn, auroras appear to be powered mainly by the solar wind, similar to Earth. However, Jupiter's auroras are more complex. Jupiter's main auroral oval is linked to plasma from its volcanic moon Io and the movement of this plasma in Jupiter's magnetosphere. Some of Jupiter's auroras are also powered by the solar wind. The moons, especially Io, create auroras through electric currents along magnetic field lines. These currents are caused by the movement of the rotating planet and the moving moon. Io, which has volcanoes and an ionosphere, is a strong source of auroras. These currents also produce radio emissions studied since 1955. Auroras have been observed over Io, Europa, and Ganymede using the Hubble Space Telescope.

Auroras have also been seen on Venus and Mars. Venus has no magnetic field, so its auroras appear as bright, diffuse patches of varying shapes and sizes across its surface. These auroras form when electrons from the solar wind collide with Venus's night side.

On Mars, an aurora was detected on August 14, 2004, by the SPICAM instrument on the Mars Express spacecraft. It was located near Terra Cimmeria, at 177° east, 52° south. The aurora was about 30 km wide and possibly 8 km high. Scientists found that the aurora occurred in an area with the strongest magnetic field on Mars, suggesting that electrons moved along magnetic lines to create the light.

Between 2014 and 2016, auroras were observed on comet 67P/Churyumov–Gerasimenko by the Rosetta spacecraft. These auroras appeared in far-ultraviolet light. Observations showed emissions of hydrogen and oxygen from water molecules in the comet's coma, caused by sunlight breaking apart the molecules. Accelerated electrons from the solar wind interacting with gas particles in the coma create the aurora. Since 67P has no magnetic field, the aurora spreads out around the comet.

Exoplanets, like hot Jupiters, may experience ionization in their upper atmospheres and generate auroras influenced by weather in their atmospheres. However, no auroras on exoplanets have been detected yet.

In July 2015, auroras were discovered on the brown dwarf star LSR J1835+3259. These auroras were mostly red and a million times brighter than Earth's northern lights, caused by charged particles interacting with hydrogen in the star's atmosphere. Scientists think stellar winds may remove material from the star's surface to create electrons, or an unseen object may be sending material into space, similar to how Jupiter's moon Io affects Jupiter.

X-ray auroras have been observed on Mercury by the Mariner 10 and MESSENGER missions. Because Mercury's exosphere is very thin, these emissions occur on its surface instead of in its atmosphere. In 2023, the BepiColombo mission found electromagnetic waves near Mercury's surface that scatter electrons, creating the X-ray aurora.