An aurora is a natural light show in Earth's upper atmosphere. It happens when charged particles from the Sun hit atoms in the atmosphere. This makes oxygen and nitrogen glow in colors like green, red, and purple. In areas near the poles, 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 create bright, moving patterns in the sky that look like curtains, rays, spirals, or flickering lights.

Auroras happen because of changes in Earth's magnetic field caused by fast-moving solar wind from areas on the Sun called coronal holes and coronal mass ejections. These changes affect the paths of charged particles in the magnetosphere. These particles, mostly electrons and protons, fall into the upper layers of the atmosphere (thermosphere/exosphere). This causes the air to become charged and glow with different colors. The shape of the aurora, which appears in bands around the poles, depends on how fast the particles move.

Other planets, brown dwarfs, comets, and some moons in our Solar System 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 studied the writings of Galileo Galilei, who used the term in his long writings about auroras in 1619. The term became part of 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 announce the arrival of the Sun. The word "aurora" was first used in English in the 14th century. The words "borealis" and "australis" are based on the names of ancient Greek gods: Boreas, the god of the north wind, and Auster, the god of the south wind.

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

Characterisation

Auroras are most often seen in the "auroral zone," a narrow band of Earth's surface about 6° wide (around 660 km) in latitude, centered at 67° north and south. The area where auroras are currently visible is called the "auroral oval." This oval moves due to the solar wind, shifting about 15° away from the geomagnetic pole (not the geographic pole) toward the noon side and 23° away toward the midnight side. The oval's farthest point toward the equator is slightly offset from geographic midnight. It is centered about 3–5° nightward of the magnetic pole, so auroral arcs reach farthest toward the equator when the magnetic pole is between the observer and the Sun, a time called magnetic midnight.

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

In northern regions, auroras are called the aurora borealis or northern lights. The southern version, aurora australis or southern lights, has similar features and changes at the same time as the northern auroras. The southern lights are visible from areas like Antarctica, Patagonia, southeastern Australia, New Zealand, and the Falkland Islands. The northern lights appear in Arctic regions such as Alaska, Canada, Iceland, Greenland, the Faroe Islands, Scandinavia, Finland, Scotland, and Russia. During geomagnetic storms, auroral ovals expand, making auroras visible at lower latitudes in the north or higher latitudes 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, Western Australia, and Uruguay. During the Carrington Event, the largest geomagnetic storm ever recorded, auroras were visible even in the tropics.

Auroras within the auroral oval may appear directly overhead. From farther away, they glow greenish or faint red on the horizon, like the Sun rising from an unusual direction. Auroras also occur poleward of the auroral zone as faint patches or arcs.

Auroras can sometimes be seen below the auroral zone during geomagnetic storms, which temporarily expand the auroral oval. Large geomagnetic storms often happen 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 speed, called the "pitch angle." The distance of the electron from the field line is its "Larmor radius." As the electron moves into stronger magnetic fields near Earth's atmosphere, its pitch angle increases. If the angle reaches 90° before entering the atmosphere, the electron may return, or "mirror," instead of colliding with molecules. Other electrons enter the atmosphere and create auroras at different altitudes. Other auroras, like "poleward arcs," "theta auroras," and "dayside arcs," have been observed from space but 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 near Earth's polar cusps, where magnetic field lines separate.

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

According to Clark (2007), five main aurora forms can be seen from Earth, from least to most visible:

Brekke (1994) also described some auroras as "curtains," a term enhanced by folds in the arcs. Arcs can break into separate, changing features that may fill the sky. These are called discrete auroras, which are sometimes bright enough to read by.

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

Auroras change over time. At night, they begin as glows and may progress to coronas, though they may not reach that stage. They often fade in the opposite order. Until 1963, scientists thought these changes were due to Earth's rotation under a fixed pattern relative to the Sun. Later, studies showed auroras undergo global changes in a process called auroral substorm. They shift rapidly from quiet arcs to active displays and then gradually return to calm. These changes are often visualized using keograms.

At shorter time scales, auroras may change slowly or rapidly, even down to sub-second intervals. Pulsating auroras, for example, show intensity changes every 2–20 seconds. These auroras are linked to faster solar wind speeds and lower emission heights for blue and green light.

Auroras also produce strong radio waves at 150 kHz, called auroral kilometric radiation (AKR), discovered in 1972. These waves are only detectable from space due to absorption in Earth's ionosphere. X-ray emissions from auroral particles have also been observed.

A crackling noise, heard about 70 meters above Earth's surface, is caused by charged particles in an inversion layer of the atmosphere formed during cold nights. These particles discharge when sunlight hits the layer, creating the sound.

In 2016, over 50 citizen science reports described a new type of aurora called "STEVE," short for "Strong Thermal Emission Velocity Enhancement." STEVE is not an aurora but a ribbon of hot plasma at 450 km (280 mi) altitude, 3,000°C (5,430°F) and moving at 6 km/s (3.7 mi/s). It is linked to a picket-fence aurora, which appears outside the auroral oval closer to the equator. When STEVE and the picket-fence aurora occur together, the latter is below STEVE.

In 2020, Finnish citizen scientists discovered the "dune aurora," a phenomenon with regularly spaced, parallel green stripes in the diffuse aurora, resembling sand dunes. This is believed to be caused by changes in atomic oxygen density.

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 strength of the solar wind varies, leading to different effects, which may include one or more of the following physical processes.

Scientists do not fully understand all the details of these processes. However, it is clear that the main source of particles that create auroras comes from the solar wind, which enters Earth's magnetosphere. The magnetosphere holds radiation zones and temporarily traps particles within Earth's magnetic field. These particles are then accelerated by specific processes.

In 1960, a rocket flight from Fort Churchill in Canada discovered a stream of electrons entering Earth's atmosphere from above. 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 are accelerated during the final part of their journey into the atmosphere. These electrons often, but not always, 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 types of auroras have a smooth decrease in energy levels and a distribution that favors directions perpendicular to Earth's magnetic field. Pulsations were found to occur near the equatorial crossing point of magnetic field lines in the auroral zone. Protons are also linked to auroras, both bright and diffuse.

Auroras happen when photons are emitted in Earth's upper atmosphere, above 80 km (50 miles), as ionized nitrogen atoms gain electrons and oxygen atoms and nitrogen-based molecules return to their normal state from an excited state. These emissions are caused by collisions with particles that fall into the atmosphere. Both electrons and protons can be involved. Excitation energy is released as a photon or absorbed through collisions with other atoms or molecules.

Oxygen behaves differently compared to other elements. It takes about 0.7 seconds for oxygen to emit green light at 557.7 nm and up to two minutes for red light at 630.0 nm. Collisions with other atoms or molecules absorb this energy and stop emissions, a process called collisional quenching. At higher altitudes, where oxygen is more common and air is less dense, collisions are rare, allowing oxygen to emit red light. At lower altitudes, where air is denser, collisions are more frequent, preventing red emissions and even green ones.

The change in auroral color with altitude is explained by these factors. Oxygen red light is most common at high altitudes, followed by oxygen green and nitrogen blue, purple, or red. At lower altitudes, nitrogen blue, purple, or red dominates because collisions block oxygen emissions. Green is the most common color, followed by pink (a mix of green and red), then pure red, yellow (a mix of red and green), and finally pure blue.

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

Bright auroras are often linked to Birkeland currents, which flow into the ionosphere on one side of Earth's poles and out on the other. Some of these currents pass through the ionospheric E layer (125 km), while others take a different path through field lines closer to the equator and connect through the "partial ring current" carried by magnetically trapped plasma. The ionosphere acts like a conductor, and some scientists believe a voltage from an unknown dynamo mechanism drives these currents. Measurements from orbiting probes suggest voltages of up to 200,000 volts during intense magnetic storms. Another view suggests these currents result directly from electrons being accelerated by wave/particle interactions.

Ionospheric resistance creates a secondary Hall current flow. The magnetic disturbance on Earth's surface from the main current mostly cancels 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 used to measure auroral activity. Kristian Birkeland found that these currents flow east-west along auroral arcs and were later named "auroral electrojets." The ionosphere can help form 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 surrounded by the solar wind, a stream of hot, magnetized plasma (a gas made of free electrons and positive ions) that flows outward from the Sun in all directions. This flow is caused by the extremely high temperature of the Sun’s outer layer, called the corona. The solar wind reaches Earth with a speed of about 400 kilometers per second, a density of around 5 ions per cubic centimeter, and a magnetic field strength of about 2–5 nanotesla (for comparison, Earth’s surface magnetic field is usually 30,000–50,000 nanotesla). 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. Since the 1830s, it has been known that when an electrical conductor moves through a magnetic field in a direction that cuts across the field lines, an electric current is created in the conductor. The strength of this current depends on the speed of the movement, the strength of the magnetic field, the number of conductors, and the distance between the conductor and the magnetic field. The direction of the current depends on the direction of the movement. This process, called the "dynamo effect," is used in dynamos and applies to all conductors, including plasmas and other fluids.

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

The solar wind and magnetosphere are two electrically conducting fluids in motion relative to each other. In theory, this motion could generate electric currents through the dynamo effect, transferring energy from the solar wind to the magnetosphere. However, plasmas conduct electricity more easily along magnetic field lines than across them, which limits this process. Instead, energy is more efficiently transferred when the magnetic field lines of the solar wind connect temporarily to those of the magnetosphere. This process is called magnetic reconnection. It occurs 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 frequent 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 an obstacle that diverts the solar wind, forming a boundary about 70,000 kilometers (11 Earth radii or R e) from Earth. This boundary is preceded by a bow shock located 12,000 to 15,000 kilometers (1.9 to 2.4 R e) further out. The magnetosphere is about 190,000 kilometers (30 R e) wide near Earth, and on the night side, a long "magnetotail" of stretched magnetic field lines extends far beyond Earth, more than 200 R e from Earth.

The high-latitude region of the magnetosphere contains plasma from the solar wind. The amount of plasma entering the magnetosphere increases 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 the high-latitude geomagnetic field lines. Plasma in the magnetosphere generally flows 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 loses it to the atmosphere in the auroral zones. The cusps of the magnetosphere, which separate geomagnetic field lines that loop through Earth from those that extend into space, allow a small amount of solar wind to reach the top of Earth’s atmosphere, creating an auroral glow.

On February 26, 2008, the THEMIS probes identified, for the first time, the event that triggers the start of magnetospheric substorms. Two of the five probes, positioned about one-third the distance to the Moon, detected signs of a magnetic reconnection event 96 seconds before auroral activity intensified.

Geomagnetic storms that cause auroras may occur more frequently during the months around the equinoxes. The reasons for this are not fully understood, 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 of the Sun, which is tilted by 8 degrees. Similarly, Earth’s 23-degree axial tilt changes the angle at which Earth’s magnetic field meets the IMF throughout the year. These factors can cause small, regular changes in how the IMF connects to the magnetosphere, influencing 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 to networks of connected events.

Auroral particle acceleration

There are many types of auroras, and each has different ways that cause particles to move into Earth's atmosphere. The auroras seen in Earth's auroral zone (the area where auroras are commonly visible) can be divided into two main types: diffuse and discrete. Diffuse auroras look unstructured to someone on the ground, with unclear edges and shapeless forms. Discrete auroras have clear, organized shapes, such as arcs, rays, and coronas, and are usually much brighter than diffuse auroras.

In both cases, the electrons that create auroras begin as particles trapped by Earth's magnetic field in the magnetosphere. These particles move back and forth along magnetic field lines and are kept from entering the atmosphere by the magnetic mirror effect, which occurs because the magnetic field becomes stronger closer to Earth. The magnetic mirror's ability to trap a particle depends on the particle's pitch angle—the angle between its movement and the magnetic field. Auroras form when processes change the pitch angle of many electrons, allowing them to escape the magnetic trap and enter the atmosphere.

For diffuse auroras, the pitch angles of electrons change due to their interaction with plasma waves. Each interaction causes the electrons to scatter, altering their direction of motion without changing their energy much. If the final direction of motion is close to the magnetic field line (within the loss cone), the electron will enter the atmosphere. Diffuse auroras occur 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, leading to more diffuse auroras.

For discrete auroras, trapped electrons are accelerated toward Earth by electric fields that form at an altitude of about 4,000–12,000 km in the "auroral acceleration region." These electric fields point upward along the magnetic field line. Electrons moving downward through these fields gain energy (about a few thousand electron volts) in the direction of Earth. This acceleration reduces the pitch angle of all electrons passing through the region, causing many to enter the upper atmosphere. Unlike the scattering process that causes diffuse auroras, the electric field increases the energy of all electrons moving through the acceleration region by the same amount. This allows electrons with low initial energy (tens of electron volts) to gain enough energy (hundreds of electron volts or more) to create auroras.

The accelerated electrons carry an electric current along the magnetic field lines (called a Birkeland current). Since the electric field and current move in the same direction, energy from the electromagnetic field 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 way this energy moves through the magnetosphere is still being studied. Although the energy for auroras comes from the solar wind, 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 Earth directly.

Some auroral features are created by electrons accelerated by dispersive Alfvén waves. At small wavelengths, these waves develop a strong electric field parallel to the magnetic field. This electric field can accelerate electrons to energies high enough to create 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 them to enter the atmosphere. Electrons accelerated this way have a wide range of energy levels, unlike those accelerated by electric fields that change slowly, which have a more narrow energy range.

In addition to diffuse and discrete auroras, proton auroras occur when magnetospheric protons collide with the upper atmosphere. During this collision, the proton gains an electron, forming a neutral hydrogen atom that emits light. However, this light is too dim to see with the naked eye. Other auroras not covered here include transpolar arcs (formed north or south of the auroral zone), cusp auroras (formed in two small areas on the day side of Earth), and auroras on other planets.

Historically significant events

In 2017, a diary from 1770 was discovered in Japan. It showed auroras above Kyoto, the ancient capital of Japan. This suggested that the storm might have been 7% stronger than the Carrington Event, which caused problems for telegraph networks.

The Carrington Event caused auroras on August 28 and September 2, 1859. These auroras are considered the most intense in recent history. In 1861, Balfour Stewart wrote a paper for the Royal Society. He described auroras recorded by a self-recording magnetograph at Kew Observatory. He connected the aurora on September 2, 1859, to the Carrington–Hodgson solar flare. He noted, "It is not impossible to suppose that in this case our luminary was taken in the act." The aurora on September 2, 1859, was caused by a coronal mass ejection linked to the powerful 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 bright that ordinary print could be read by its light" at 1:00 a.m. Eastern Time. At that time, the magnetograph at Kew Observatory was recording the geomagnetic storm at its strongest point. Between 1859 and 1862, Elias Loomis published nine papers in the American Journal of Science, collecting global reports about the 1859 auroral event.

This aurora is believed to have been caused by one of the most powerful coronal mass ejections in history. It is also notable for being the first time auroras and electricity were clearly linked. This discovery was supported by magnetometer measurements from the time and reports that telegraph lines were disrupted for many hours during the storm. Some telegraph lines were long enough and oriented correctly to allow communication without power. A conversation between two telegraph operators in Boston and Portland, Maine, on September 2, 1859, was recorded in the Boston Traveller.

Boston operator: "Please disconnect your battery for fifteen minutes."
Portland operator: "Will do so. It is now disconnected."
Boston: "Mine is disconnected. We are working with the auroral current. How do you receive my writing?"
Portland: "Better than with our batteries on. The current comes and goes gradually."
Boston: "My current is very strong at times. We can work better without batteries, as the aurora seems to neutralize and augment our batteries alternately, making the current too strong 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 lasted about two hours without using battery power. It was the first time more than a few words were transmitted using only the aurora’s current. This led to the conclusion that auroras can increase or decrease the electric current in telegraph wires. Sometimes, auroras completely stop the current, making it impossible to detect. The aurora borealis appears to consist of electric matter similar to that produced by a galvanic battery. The currents from the aurora change as they reach the wires and then disappear. The aurora moves from the horizon to the sky’s center.

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

Historical views and folklore

The earliest written record of an aurora is found in the Bamboo Annals, a historical record from ancient China, which mentions an aurora in 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 them names like "barrel-like" (pithaei), "chasm" (chasmata), "bearded" (pogoniae), and "like cypress trees" (cyparissae). He also described their colors and whether they appeared above or below clouds. He noted that during the time of Emperor Tiberius, a bright red aurora over the port city of Ostia caused soldiers nearby to ride to the rescue, thinking it was a fire. Some scholars think that Pliny the Elder described the aurora borealis in his book Natural History when he wrote about "falling red flames" and "daylight in the night."

The oldest known image of an aurora may be in cave paintings from northern Spain, dating to about 30,000 BC. The earliest written record of a wintertime aurora is in a Chinese legend from around 2600 BC. A later record of an autumn aurora is from about 2000 BC.

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

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

Among the Māori people of New Zealand, the aurora australis, called Tahunui-a-rangi ("great torches in the sky"), was said to be lit by ancestors who sailed to a "land of ice" (the Southern Ocean). These ancestors were believed to be part of the expedition led by Ui-te-Rangiora around the 7th century.

In Scandinavia, the first written mention of norðrljós (the northern lights) is in the Norwegian chronicle Konungs Skuggsjá from AD 1230. The writer learned about the lights from people who had traveled to Greenland. He suggested three possible causes: that the ocean was surrounded by fires, that the sun’s energy reached Earth’s night side, or that glaciers stored energy that made them glow.

In 1920, Walter William Bryant wrote that the astronomer Tycho Brahe believed sulfur could cure diseases caused by the "sulphurous vapours" of the aurora borealis.

In 1778, Benjamin Franklin proposed that auroras might be caused by electrical charges in the polar regions, intensified by snow and moisture. He suggested that electricity from clouds in the polar regions might travel through the air toward the equator, creating visible lights.

In 1741, scientists Anders Celsius and Olof Hiorter in Uppsala, Sweden, observed that compass needles moved rhythmically when auroras occurred. Hiorter linked these movements to magnetic changes in the air, supporting the idea that "magnetic storms" caused auroras.

Many Native American cultures have myths about auroras. In 1771, the 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.

After the Battle of Fredericksburg during the American Civil War, an aurora was seen from the battlefield. Confederate soldiers believed the lights were a sign that God supported their cause. The painting "Aurora Borealis" by Frederic Edwin Church is often interpreted as representing the American Civil War.

A British source from the mid-1800s stated that auroras were rare before the 18th century. It noted that no auroras were recorded for over 80 years before 1716, and few were seen after 1574. One aurora in 1723 at Bologna was called the first ever seen there. Scientists in Uppsala, Sweden, believed auroras were rare before 1716. This period (1645–1715) matches the Maunder minimum, a time of low sunspot activity.

In a 1908 poem titled "The Ballad of the Northern Lights," the writer Robert W. Service joked that the aurora was the glow from a radium mine discovered by a Yukon prospector.

In the early 1900s, the 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, spilled in the sky after they died from cutting themselves. Many Indigenous groups in northern Eurasia and North America share similar beliefs, thinking auroras are the blood of

Extraterrestrial auroras

Auroras have been seen on all planets with magnetic fields, except Neptune. The physical process that creates auroras is the same, but the results can be very different.

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

On Saturn, auroras appear to be powered by the solar wind, similar to Earth's auroras. However, Jupiter's auroras are more complex. Jupiter's main auroral oval is linked to plasma created by the 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, but the exact amount is unknown. The moons, especially Io, are strong sources of auroras. These auroras are caused by electric currents along magnetic field lines, created by the movement between Jupiter and Io. Io, which has active volcanoes and an ionosphere, is a major source of these currents. 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 intensity, sometimes covering the entire planet. Venusian auroras occur when electrons from the solar wind collide with the night side of Venus's atmosphere.

An aurora was detected on Mars on August 14, 2004, by the SPICAM instrument on the Mars Express spacecraft. The aurora was located at Terra Cimmeria, near 177° east, 52° south. The aurora's emission area was about 30 kilometers wide and possibly 8 kilometers high. Scientists used data from the Mars Global Surveyor to map magnetic anomalies on Mars and found that the aurora's location matched a region with the strongest magnetic field. This suggests the aurora was caused by electrons moving along magnetic field lines and exciting Mars's upper atmosphere.

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

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

The first auroras discovered outside our solar system were found in July 2015 on the brown dwarf star LSR J1835+3259. These auroras were mainly 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 be removing material from the brown dwarf to create electrons, or an undetected object orbiting the star may be causing material to be released, similar to how Jupiter's moon Io affects Jupiter.

X-ray auroras have been observed on Mercury by the Mariner 10 and MESSENGER missions. However, because Mercury's exosphere is very thin, these emissions occur on Mercury's surface, not its atmosphere. In 2023, the BepiColombo mission found electromagnetic waves within 1,200 kilometers of Mercury's surface, scattering electrons believed to create the X-ray aurora.