48 Fun Facts About Aurora

What causes an aurora?

Solar particles hitting atoms in the upper atmosphere make the thin gas glow much as electricity lights a neon sign, which is why the biggest displays follow eruptions on the Sun.

Why can the northern lights almost never be seen from the Arctic in midsummer?

The sky never gets dark enough under the midnight sun: the aurora carries on overhead but only shows against a dark sky, and displays tend to peak around the spring and autumn equinoxes.

The word 'aurora' comes from the Roman goddess of what?

The dawn is what the lights resembled to Europeans far from the Arctic, who usually saw only a faint reddish glow low in the north, as if the Sun were about to rise in the wrong place.

Who is often credited with coining the term 'aurora borealis' in a 1619 treatise published under a pupil's name?

Galileo Galilei wrongly took the lights for sunlight bouncing off the high atmosphere; Pierre Gassendi, sometimes given the credit instead, used the name in a 1649 account of a 1621 display.

Which colour of aurora is the most common?

Green dominates, though often less vividly than photos suggest: long camera exposures record colour in displays that look pale, or even invisible, to the people standing beneath them.

Which gas emits the deep red light sometimes seen at the very top of an aurora?

Atomic oxygen needs about two minutes undisturbed to release its red light, so the colour survives only in the near-vacuum at the top of a display; lower down, collisions snuff it out first.

The purple fringe sometimes seen along the lower edge of an aurora's curtains is emitted by which gas?

Molecular nitrogen is so stable that it rarely splits into atoms, so it glows as whole molecules, and its purple hem shows up only in the most intense displays.

Which Norwegian city sits in the auroral zone, where the northern lights appear most often?

Tromsø lies beneath the band the lights form around the magnetic pole, so displays there can pass straight overhead, and the town has had an auroral observatory since the 1920s.

What do scientists call the glowing band that an aurora traces around the pole when seen from space?

The auroral oval swells toward the equator when a solar storm hits, which is why forecasters map it to tell people far from the poles when to look up.

Carl Størmer triangulated thousands of auroras with cameras across Norway and found most glowed at about what altitude?

About 100 km up is roughly where space is said to begin; Størmer, a pure mathematician, owed his method to a student hobby of secretly snapping Oslo passers-by with a hidden camera.

Which name describes auroras seen from directly below, their rays fanning out from one point overhead?

Coronas are a trick of perspective: the rays are tall parallel columns of light, and seen from underneath they appear to converge the way railway tracks do in the distance.

The very brightest auroras have reportedly given enough light to do what at night?

Read a newspaper is what people in the north-eastern United States did by the great aurora of 1859, a display so bright that others got up and started their morning chores, sure the Sun was rising.

Large geomagnetic storms that push auroras to lower latitudes are most common around the peak of what?

The 11-year sunspot cycle is at heart a magnetic one: near each peak the Sun's two magnetic poles swap places, and the eruptions that drive great storms multiply.

Which 1859 event, the greatest geomagnetic storm on record, brought auroras to the tropics?

The Carrington Event is named for the English amateur astronomer who, sketching sunspots the morning before, saw two patches of white light flare over them: the first solar flare ever recorded.

A scholar's diary helped researchers reconstruct a vast red aurora that filled the sky in 1770 over which old Japanese capital?

Kyoto lies so far from the pole that an aurora overhead means an extreme storm; the diarist noted where the red light sat against the Milky Way, and that let researchers rate it on a par with 1859's.

Why did some American farmers stop planting during the May 2024 solar storm that spread auroras worldwide?

Their tractors lost GPS guidance: self-steering rigs need inch-level satellite fixes to plant straight rows, and the storm scrambled them days before the Midwest's mid-May deadline for corn.

Which first name did Alberta aurora chasers give a mysterious purple ribbon of light, borrowing it from the film Over the Hedge?

Steve is what the film's animals call a hedge that appears overnight, to make it less frightening; scientists later bent the name into an acronym, Strong Thermal Emission Velocity Enhancement.

Finnish hobbyists who spotted a new aurora form, a row of evenly spaced stripes, named it after which landscape feature?

Dunes were missing from an aurora guidebook a Helsinki physicist had just written for the hobbyists, and they told her so; photos they then took at the same moment from two towns let her team measure the stripes' height.

Electrons cause most auroras, but which other particle from space produces a fainter kind usually invisible to the naked eye?

Proton auroras glow by theft: each incoming proton steals an electron, turns into a hydrogen atom and gives off light of its own, spread too thinly for most eyes to notice.

Pulsating auroras are faint patches that blink on and off, with each cycle lasting roughly how long?

2 to 20 s is the beat of 'chorus' waves far out in Earth's magnetic field, so called because they sound like chirping birds as audio; each chirp knocks a burst of electrons down into the air.

Comet tails always point away from the Sun, a clue that led scientists to predict which particle flow that also powers auroras?

The solar wind was worked out on paper in 1958 by Eugene Parker, whose referees called the idea absurd; the journal's editor printed it anyway, and a Soviet Moon probe detected the flow within months.

Earth's magnetic field points north, so auroras tend to flare when the magnetic field arriving from the Sun points which way?

Southward is the word aurora chasers wait for: opposite fields link up like two bar magnets snapping together and let the Sun's particles pour in, while a northward field mostly slides past.

Which Norwegian physicist made artificial auroras by firing electrons at a magnetised globe in a vacuum chamber around 1900?

Kristian Birkeland paid for his aurora work with inventions, among them an electric cannon that short-circuited and spat flames before an invited Oslo audience in 1903.

Which Swedish astronomer, working with his assistant Olof Hiorter, noticed in 1741 that compass needles swung when an aurora was overhead?

Anders Celsius also built the thermometer that bears his name, but upside down: he put 0 at boiling and 100 at freezing, and the scale was flipped only after his death in 1744.

Benjamin Franklin wrote a paper suggesting that auroras were caused by what?

Electrical charge concentrated in the polar regions was a natural guess for the man of the kite and the lightning rod, and he was half right: the lights are electrical, though the charge arrives from the Sun.

Which NASA mission, named for a Greek goddess, used five probes to settle what triggers the substorms that brighten auroras?

THEMIS was named for the Greek goddess of justice because it had to judge between two rival theories; its probes caught magnetic field lines snapping a third of the way to the Moon about a minute and a half before the lights flared.

Jupiter's main auroral ring is associated with plasma produced by which moon?

Io's volcanoes throw debris into space, and Jupiter's fast-spinning magnetic field whips it up and channels it toward the poles, so these lights can shine without any help from the Sun.

Why do Venus's faint auroras spread in patches across its night side instead of circling the poles?

Venus has no magnetic field of its own to steer incoming particles toward the poles, so they strike the night-side air wherever they arrive; the light is so weak that some scientists dispute calling it an aurora.

Earth's auroras circle the poles, but where did Mars Express spot the first aurora ever detected on Mars?

Over magnetised patches of crust in the southern hemisphere: Mars lost its global magnetic field long ago, but old rock still holds traces of it, and the glow seen there in 2004 was only about 30 km wide.

On which planet do X-ray auroras occur on the surface rather than in an atmosphere?

Mercury has almost no air, so electrons raining in from space slam straight into bare rock and make the ground itself give off X-rays, a process the BepiColombo probe caught during a 2021 flyby.

Which spacecraft, orbiting comet 67P from 2014 to 2016, detected the first ultraviolet aurora ever seen at a comet?

Rosetta's team first filed the glow under 'dayglow', gas lit up by sunlight itself; in 2020 they showed that electrons streaming from the Sun were doing it, at a comet with no magnetism of its own to steer them.

The first auroras found beyond the solar system, on a failed star in 2015, were roughly how much brighter than Earth's?

A million times brighter is the discoverers' rough estimate; the glow would be bright red, since a brown dwarf's atmosphere is rich in hydrogen, though anyone watching from its surface would face about 100 times Earth's gravity.

Which civilisation's annals describe a 'five-coloured light' in the tenth century BC, perhaps the earliest datable report of an aurora?

China's Bamboo Annals place the light in the northern night sky late in King Zhao's reign; it went unnoticed because a 16th-century edition turned the light into a comet, and it predates Assyrian tablets by three centuries.

Under Tiberius, a glow now thought to be an aurora sent Roman cohorts rushing to Ostia, believing what?

The town was on fire, they assumed: the philosopher Seneca, who tells the story, says the sky over the port glowed dully for most of the night, like thick, smoky flame seen from a distance.

Which explanation for the northern lights did the medieval Norwegian book The King's Mirror find most plausible?

Glaciers storing energy until they glow beat two rival guesses in the book, a blaze ringing the outer ocean and sunlight leaking up from below the horizon; its author adds that Greenlanders could hunt by the lights.

Which long-doubted claim about the northern lights did Finnish researchers confirm in 2012?

They make faint sounds, a crackle born only about 70 metres overhead; the team's theory is that on cold, still nights a lid of warm air traps charge until a magnetic storm sets it sparking.

In one Māori tradition, what is the aurora australis?

Fires lit by kin far south: in the story, some of the first voyagers sailed on past New Zealand and settled, and their descendants light great blazes as a signal to their relatives back home.

Sami tradition held that the northern lights were souls of the dead, so children were warned never to do what?

Whistle at them, the warning went, and the lights would notice you, sweep down and carry you off; waving was just as risky, and some families kept children indoors whenever a strong display was overhead.

Samuel Hearne's Dene guides named the northern lights after which animal, whose stroked fur throws sparks in the dark?

Caribou were the herds the Dene lived on, and a bright display meant plenty of them up in the sky; Hearne added drily that his guides never went so far as to hope to taste those celestial animals.

After which Confederate victory in December 1862 did an aurora over Virginia strike some Southern soldiers as heaven celebrating with them?

Fredericksburg's losers claimed the lights as well: Joshua Chamberlain, burying Union dead that night, wrote that the North had lifted her own glorious lights to honour them.

Aurora reports across Europe grew scarce between 1645 and 1715, a period matching what?

The Maunder minimum in sunspots was long blamed on lazy observers, until John Eddy used old records and tree rings in 1976 to show that the Sun really had gone quiet for seventy years.

In Robert Service's 'The Ballad of the Northern Lights', a ragged prospector swears the aurora is the glow from what?

A radium mine worth millions is what he claims to have staked, yet he ends the poem offering a quarter share for a hundred dollars, then for ten, and finally just asking to borrow a dollar.

In The Simpsons, who scoffs when Principal Skinner passes off the glow from his kitchen as the aurora borealis?

Superintendent Chalmers lists all that is wrong with the excuse, from the season to the time of day; the 1996 'Steamed Hams' sketch became a meme twenty years on, and when real auroras swept the US in May 2024, fans all posted the joke.

Tycho Brahe took the aurora for fumes that bred disease and, reasoning that like cures like, prescribed what?

Sulphur, purified and made into a pleasant drink, was his answer to an illness he thought sulphurous by nature; a later biographer called him something of a homeopath, and he gave his popular elixirs away free.

The 'borealis' in aurora borealis comes from Boreas, the Greek god of what?

The north wind had an upside for the Greeks, who imagined a blissful people, the Hyperboreans, living just beyond his reach; aurora australis takes its name from Auster, his southern opposite.

In 1962, what lit up auroras seen from Hawaii to New Zealand?

A nuclear test in space, Starfish Prime, burst 400 km above the Pacific; its pulse blacked out streetlights in Honolulu, and the radiation it left in orbit went on to cripple satellites, Britain's first among them.

Paired jets over Alaska and south of New Zealand found in the 1960s that the northern and southern lights often do what?

Mirror each other is what the twin displays, known as conjugate auroras, did on quiet nights; in 2009, though, satellites watching both poles at once caught the two badly mismatched.

In March 1989, a solar storm that spread auroras as far south as Texas blacked out which Canadian province for nine hours?

Quebec sits on ancient rock that conducts electricity poorly, so the storm's currents surged into Hydro-Québec's very long power lines instead, and the whole grid tripped in under two minutes.