100 Fun Facts About Stars

The few thousand stars visible to the naked eye all lie within which galaxy?

The Milky Way. Stars in other galaxies are far too distant to pick out one by one, so even on the darkest night the eye catches only a few thousand of our own galaxy's nearest and brightest.

The Big Bang made hydrogen, helium and a trace of which element, leaving stars to forge nearly all the rest?

Lithium. The Big Bang's burst of fusion was over within minutes as the universe cooled, long enough to build only the very lightest nuclei, so heavier elements had to wait for stars.

Which English word for a catastrophe comes from the Italian for "ill-starred"?

Disaster. It joins dis- to astro, "star", because astrologers once blamed a sudden misfortune on an unfavourable position of the planets.

Ancient Egyptians watched for the dawn return of which star because it heralded the Nile's annual flood?

Sirius. Its first dawn appearance came like clockwork just before the flood each summer, so Egyptians worshipped the star as Sopdet, the goddess who brought the new year and the flood.

Which astronomers were the first to record a supernova, in 185 AD?

Chinese. Their astronomers logged a "guest star" that lingered for about eight months, and four space telescopes have since matched it to RCW 86, a glowing shell of debris in the southern sky.

The supernova of 1054 gave birth to which famous object?

The Crab Nebula. Skywatchers in 1054 saw the blast as a new star bright enough to show in daytime for about three weeks, and the cloud it flung out is still expanding.

Which galaxy did the Persian astronomer al-Sufi record as a "little cloud" in his Book of Fixed Stars?

The Andromeda Galaxy. Al-Sufi's note of 964 is its first known record, yet nobody knew the smudge was a separate galaxy until Edwin Hubble measured its distance in the 1920s.

Who suggested in 1584 that stars were suns that might have their own planets?

Giordano Bruno. He pictured an infinite universe of countless worlds, and the Roman Inquisition, which tried him for heresy, had him burned at the stake in 1600.

Who discovered that some paired stars are true physical companions, or binaries?

William Herschel. He tracked double stars hoping their shifts would reveal their distances, but after 25 years of watching he found that some pairs were instead circling each other.

Who made the first direct measurement of a star's distance, in 1838?

Friedrich Bessel. He chose the dim star 61 Cygni because it drifted across the sky faster than any other he had charted, guessing rightly that it must be close, then caught its tiny yearly shift.

Which star in the Big Dipper's handle was the first known spectroscopic binary?

Mizar. Harvard astronomers saw a dark line in its spectrum split in two and merge again, betraying a pair of stars too close together for telescopes of the day to separate.

Who made the first measurement of a star's diameter, in 1921?

He used an interferometer on the Hooker telescope at Mount Wilson.

The Hertzsprung–Russell diagram plots a star's luminosity against which other property?

Temperature. Ejnar Hertzsprung and Henry Norris Russell drew the plot independently around 1911–13, and the patterns stars made on it became astronomers' main tool for working out how stars age.

Whose 1925 PhD thesis first proposed that stars are mostly hydrogen and helium?

Cecilia Payne-Gaposchkin. The eminent Henry Norris Russell told her the result was "clearly impossible", so she played it down in print; four years later he reached the same conclusion himself.

Which astronomer labelled stars in each constellation with Greek letters around 1600?

Johann Bayer. He was a lawyer rather than a working astronomer, yet the lettering scheme in his 1603 atlas Uranometria caught on so well that astronomers still use it four centuries later.

Which well-known nebula is a stellar nursery where new stars are forming?

The Orion Nebula. It is the closest large star-forming region to Earth, which is why it can be spotted without a telescope as the fuzzy middle "star" of the hunter's sword.

The Pillars of Creation, towering columns of star-forming gas photographed by Hubble, lie in which nebula?

The Eagle Nebula. Its columns stand several light-years tall, yet the fierce light and winds of young stars nearby are slowly wearing them away even as new stars form inside.

A star spends about 90% of its life in which stage, steadily fusing hydrogen in its core?

The main sequence. It ends when the core runs out of hydrogen: with nothing left to hold it up, the core starts to collapse and heat, and the star's outer layers slowly puff up.

Stars twinkle because their light is distorted on its way through what?

Earth's atmosphere. Layers of air at different temperatures bend a star's pinpoint of light this way and that, while planets, which show tiny discs, usually shine steadily.

How long is the Sun expected to live in total?

10 billion years. That long life comes from modest size: heavier stars hold more fuel but burn it so fiercely that the biggest are gone within a few million years.

Which stars burn their fuel so slowly that they could shine for trillions of years?

Red dwarfs. They are so thrifty that not one has ever died of old age: at 13.8 billion years, the universe is still far too young for even the earliest of them to have run dry.

Astronomers call all elements heavier than helium what?

Metals. To an astronomer even oxygen and carbon count as metals, and because stars are what forge them, the very first stars are thought to have held virtually none.

When its core hydrogen runs out in about five billion years, the Sun will swell into what kind of star?

A red giant. Estimates of how far it will swell run from about 100 to 250 times its present width, enough to engulf Mercury and Venus and possibly Earth as well.

What is the explosive onset of core fusion in an ageing low-mass star called?

Helium flash. In heavier stars helium fusion starts gently, but a Sun-like star's core is packed so tightly that it cannot expand to cool itself, so the burning runs away.

A dying low-mass star ejects its outer layers to form what?

A planetary nebula. The name is a mistake that stuck: through early telescopes these glowing shells looked like the round discs of planets, though they have nothing to do with them.

Very massive stars that shed their outer layers become what kind of star?

Wolf–Rayet. The type is named after Charles Wolf and Georges Rayet, who found the first ones from Paris in 1867; it is a brief phase that only some massive stars pass through before they explode as supernovae.

Fusion stops releasing energy once a massive star's core starts producing which element?

Iron. Fusing it soaks up energy instead of releasing it, so the core abruptly loses the pressure holding it up, collapses in on itself and sets off a supernova.

Which star's 19th-century "Great Eruption" was a supernova impostor event?

Eta Carinae. In the 1840s it briefly became the second-brightest star in the sky while hurling off some ten Suns' worth of gas, a blast that should have torn it apart, yet it survived.

A stellar remnant below about 1.4 solar masses becomes what?

A white dwarf. It crams roughly a Sun's worth of matter into a ball the size of Earth, and with no fusion left to heat it, it simply cools and fades over billions of years.

What is the nearest star to Earth after the Sun?

Proxima Centauri. Despite being our closest neighbour it is far too faint to see without a telescope, so it went unnoticed until 1915; a planet found in 2016 orbits in its habitable zone.

Stellar collisions in dense clusters can produce which stars that look far younger than their neighbours?

Blue stragglers. They still burn hot and blue when cluster-mates born at the same time have swollen and reddened, because colliding with or stealing gas from a neighbour tops up their fuel.

One of the oldest known stars, HD 140283, is nicknamed after which biblical figure?

Methuselah. A 2013 Hubble study put its age at about 14.5 billion years, older than the universe itself; only the wide margin of error on that figure rescues it from paradox.

Which star cluster in Taurus is popularly known as the Seven Sisters?

The Pleiades. In Japan the cluster is called Subaru, which is why a handful of its stars shine from the badge of every Subaru car.

Which star sits almost directly above Earth's northern axis, so the rest of the night sky appears to wheel around it?

Polaris. It is far from the brightest star, ranking only around 48th, and it has not always held the job: when Egypt's pyramids were built, the pole star was Thuban in Draco.

Which red supergiant in Orion is so vast that, in the Sun's place, it would swallow the orbit of Mars?

Betelgeuse. In late 2019 it dimmed so sharply that skywatchers wondered if it was about to explode; Hubble showed it had instead blown off part of its surface, which cooled into a light-blocking cloud of dust.

The star Achernar bulges far wider at its equator than at its poles because of its extreme what?

Rotation speed. Achernar whirls so fast that it is close to flying apart, and the ESO astronomers who measured its shape in 2003 called it the flattest star ever seen.

About how long does the Sun take to rotate once at its equator?

About 25 days. Its poles lag behind, taking about five weeks, a mismatch possible only because the Sun is a ball of electrically charged gas and not a solid body.

The star that exploded in 1054 left a core that now spins 30 times a second, making it which kind of object?

A pulsar. Their beat is so clockwork-regular that when the first pulsars turned up in 1967, astronomers half-jokingly labelled them LGM, for "little green men".

Which European spacecraft, launched in 2013, charted the positions and motions of more than a billion stars?

Gaia. By returning to each star again and again for years, it could watch them shift and so work out their distances and motions, building the most precise 3D map of our galaxy ever made.

Which ancient Greek astronomer is credited with first ranking the stars by brightness on a scale of magnitudes?

Hipparchus. The brightest stars were ranked first magnitude and the faintest the eye could see sixth, which is why the scale still runs backwards: the brighter the star, the lower its number.

Which unit, equal to about 3.26 light-years, do astronomers use to measure the distances to stars?

The parsec. Its name is short for "parallax second", because it is the distance at which a star appears to shift by one arcsecond as Earth orbits; absolute magnitude imagines every star placed 10 of them away.

Which spectral class contains the hottest stars?

O. The classes run O, B, A, F, G, K, M from hottest to coolest; the letters look scrambled because Annie Jump Cannon at Harvard rearranged an older alphabetical scheme once the true order was understood.

Although the Sun is classed as a "yellow dwarf", its light seen from space is actually which colour?

White. The Sun gives out all the colours of the rainbow at once, which blend to white; it only looks yellow or red from the ground because the air scatters some of its blue light away.

Which long-period pulsating variable gives its name to a class of stars?

Mira. Seventeenth-century astronomers named it "the wonderful" because it fades out of sight and then returns, brightening and dimming over about 11 months as the whole star pulses.

What is the visible surface layer of a star called?

The photosphere. Energy made in the core spends many thousands of years struggling up through the dense interior before it reaches this layer, where the gas finally turns transparent and light escapes into space.

The Sun's outermost atmosphere, seen during eclipses, is called what?

The corona. In 2021 NASA's Parker Solar Probe became the first spacecraft to fly through it, a feat the agency billed as touching the Sun.

By which reaction does the Sun mainly fuse hydrogen in its core?

The proton–proton chain. Protons repel each other so strongly that they can merge only by quantum tunnelling, which makes the process slow enough for the Sun to burn steadily for billions of years.

The triple-alpha process turns helium into carbon via which intermediate element?

Beryllium. Two helium nuclei make a beryllium-8 nucleus that falls apart again in a tiny fraction of a second, so carbon forms only if a third helium nucleus strikes before it does.

About how long does sunlight take to travel from the Sun to Earth?

About 8 minutes. That means we always see the Sun slightly out of date: if it vanished this instant, the sky would stay bright for another eight minutes or so.

What is the name for the 70-year spell with almost no sunspots in the 17th century?

The Maunder Minimum. From about 1645 to 1715 sunspots all but vanished and the Sun dimmed slightly, just as Europe and North America, already in a cold spell, went into a deep freeze.

The 'dog days' of summer take their name from which star, the brightest in Earth's night sky?

Sirius, the Dog Star, returns to the dawn sky in high summer, and the ancient Greeks tied its reappearance to heat, drought and mad dogs. It lies less than nine light-years away.

The Japanese carmaker Subaru takes its name and six-star badge from which star cluster in Taurus?

The Pleiades are known in Japan as Subaru. The badge's six stars also nod to the five companies that joined into one to build the cars.

Han Solo brags that his ship made the Kessel Run in under twelve of which units of distance?

Parsecs measure length, not time, so the boast is no speed record. One parsec is about 3.26 light-years, a scale astronomers use for the gaps between stars.

A teaspoon of material from which kind of stellar object would weigh billions of tonnes?

A neutron star packs more mass than the Sun into a ball only about 20 kilometres wide. It forms when the core of a massive star collapses in a supernova.

The brilliant 'Evening Star' that hangs low in the west after sunset is really which planet?

Venus is the brightest point of light in the night sky and always stays within about 47 degrees of the Sun, so it shows only near dusk or dawn. Some ancient cultures took its two appearances for separate stars.

What is the proper name for a 'shooting star', a streak of light from debris burning up overhead?

A meteor is usually set off by a speck no bigger than a grain of sand, heated until it glows as it rams into the upper air. A chunk that survives to reach the ground is called a meteorite.

Which small constellation appears on the national flags of Australia, New Zealand and Brazil?

The Southern Cross, known to astronomers as Crux, is the smallest of all 88 constellations. Extending its long bar about four and a half times leads the eye close to the south celestial pole.

Stars twinkle while planets mostly shine steadily; what makes starlight seen from the ground flicker?

Earth's turbulent air bends starlight this way and that on the last stretch of its journey. Planets look steadier because they show tiny discs instead of single points of light.

Which physicist bet Kip Thorne that the X-ray source Cygnus X-1 did not contain a black hole?

Stephen Hawking called the bet an insurance policy: had black holes proved not to exist, he would at least have won a magazine subscription. He conceded in 1990.

Which English word, from the Italian for 'ill-starred', once blamed bad luck on an unlucky planet?

Disaster joins dis-, here meaning ill, to astro, the Italian for a star or planet. It reached English in the 1590s by way of the French désastre.

Which star at the tip of Ursa Minor's tail barely moves while the northern sky turns around it?

Polaris lies less than one degree from the north celestial pole. Many people assume it is the sky's brightest star, yet it ranks only about 47th.

Alnitak, Alnilam and Mintaka are the evenly spaced stars of which famous pattern in the night sky?

Orion's Belt looks like three single points, but only Alnilam is one star: Alnitak is a triple system and Mintaka a quintuple. Folk names for the row include the Three Kings.

The two brightest stars in the constellation Gemini are named after which pair of mythical twins?

Castor and Pollux shared a mother, Leda, and in the best-known telling only Pollux was a son of Zeus. He asked to share his immortality with his brother, and the pair were set among the stars.

Which astronomer told viewers of his 1980 TV series Cosmos that 'we're made of star-stuff'?

Carl Sagan meant it literally: the carbon and oxygen in a human body were forged inside stars that died long ago. Cosmos has been seen by over 500 million people.

Starlight seen bending past the Sun during a 1919 eclipse confirmed whose new theory of gravity?

Albert Einstein became famous worldwide once newspapers reported Arthur Eddington's eclipse measurements. General relativity predicted twice the bending that Newton's older theory allowed.

Which astronomer reported in 1610 that his telescope showed the Milky Way to be countless faint stars?

Galileo Galilei announced it in Sidereus Nuncius, the first published scientific work based on telescope observations. The same slim book revealed four moons circling Jupiter.

Roughly how many stars do astronomers estimate the Milky Way contains, the Sun being just one?

Hundreds of billions is the best estimate: somewhere between 100 and 400 billion stars, with at least as many planets circling them.

Light leaving the Sun, the nearest star, takes roughly how long to reach Earth?

About 8 minutes is the travel time, so we always see the Sun as it was a little while ago, never as it is this instant.

Deneb, Altair, Rigel and most other traditional star names used in the West come from which language?

Arabic names took hold after Ptolemy's great star catalogue was translated into Arabic in the 8th and 9th centuries, and later into Latin. Many began as plain descriptions: Deneb means 'tail' and Rigel 'foot'.

Known in Britain as the Plough, which pattern of seven bright stars forms part of Ursa Major?

The Big Dipper has been pictured as a ladle, a plough and a wagon. Astronomers class it as an asterism, a star pattern that is not a constellation in its own right.

Cool stars glow red and warmer ones yellow or white; which colour marks the very hottest stars?

Blue marks the hottest stars, whose surfaces can top 30,000 kelvin, because most of their energy pours out at the short-wavelength end of the spectrum. It is the reverse of a bathroom tap.

Which red supergiant at the heart of Scorpius has a name meaning 'rival of Mars', a nod to its colour?

Antares earned the comparison because its reddish glow mimics the planet's. The star also swells and shrinks as it pulsates, changing its radius by about 19 percent.

Japan's Tanabata festival marks the yearly reunion of two lovers: the stars Altair and which other?

Vega stands for the weaver princess Orihime, parted from her cowherd husband by the river of the Milky Way. In 1850 it became the first star after the Sun to be photographed.

Whose 1573 book about a 'new star' blazing in Cassiopeia gave astronomy the word nova?

Tycho Brahe showed the newcomer lay beyond the Moon, upsetting the ancient belief that the heavens never change. His 'new star' was really an old one exploding as a supernova.

Hubble's 1995 photograph of star-forming gas clouds in the Eagle Nebula became famous under what name?

Pillars of Creation shows columns of gas and dust, one of them about four light-years from end to end. The James Webb Space Telescope photographed the same scene again in 2022.

Sailors once found their way by measuring a star's angle above the horizon with which instrument?

A sextant is named for its frame, an arc of roughly one sixth of a circle. Its mirrors let a navigator line up a star, or the Sun, with the horizon and read off the angle between them.

Stars seem to drift from east to west through the night, just as the Sun does, because of what?

Earth's rotation turns us eastward once a day, so the whole sky seems to wheel the opposite way. Long-exposure photographs record the motion as curved star trails.

Which Cambridge student's 'little green men' radio pulses of 1967 turned out to be the first pulsar?

Jocelyn Bell Burnell noticed the signal as a 'bit of scruff' on her chart-recorder paper. The 1974 Nobel Prize in Physics honoured the discovery, but she was not among the winners.

Which astronomer, better known for a comet, found in 1718 that the 'fixed' stars slowly move?

Edmond Halley compared his own measurements with ancient Greek records and found bright stars more than half a degree out of place. Astronomers call the slow drift proper motion.

A pulsating star found by Edwin Hubble proved which 'spiral nebula' lies far beyond the Milky Way?

The Andromeda Galaxy proved far too distant to belong to the Milky Way, settling a long debate over whether other galaxies exist at all. It lies about 2.5 million light-years away.

Which technique tells astronomers what stars are made of by spreading their light into a rainbow?

Spectroscopy works because each element blocks its own set of colours, leaving dark lines like a barcode. Joseph von Fraunhofer counted 574 such lines in sunlight in the early 1800s.

Nearby stars seem to shift against distant ones as Earth circles the Sun; what is this effect called?

Parallax shrinks with distance, so the smaller a star's shift, the farther away it lies. Even for the nearest stars the shift is so tiny that nobody managed to measure it until the 1830s.

Which Harvard astronomer, nearly deaf for most of her career, classified some 350,000 stars?

Annie Jump Cannon could classify three stars a minute just by looking at their spectral patterns. She is credited with creating the Harvard scheme that sorts stars by temperature.

Henrietta Leavitt found that which pulsating stars reveal their true brightness by how slowly they pulse?

Cepheid variables became astronomy's yardsticks: time one's pulse, work out its real output, and its faintness tells you how far away it is. Leavitt spotted the rule in 1908.

Which giant star, whose name means 'the follower', forms the bloodshot eye of Taurus the Bull?

Aldebaran got its name because it trails a famous star cluster across the sky each night. The long-dead Pioneer 10 probe is drifting in its general direction.

Which star, whose Latin name means 'little king', is the brightest in the constellation Leo?

Regulus lies closer to the ecliptic, the Sun's yearly path, than any other bright star, so the Moon often passes in front of it and briefly blots it out.

Which astronomer, who coined 'Big Bang' on BBC radio, showed how stars forge the heavier elements?

Fred Hoyle never accepted the theory he had named, arguing instead for a steady-state universe. His element work held up: he predicted a property of the carbon nucleus that experiments later confirmed.

Seen from Britain, the stars of Cassiopeia never set below the horizon; which term describes such stars?

Circumpolar stars stay in view all night on every night of the year, turning around the pole without setting. The closer an observer stands to either pole of the Earth, the more stars qualify.

The supernova seen in 1987, the closest since Kepler's in 1604, exploded in which neighbouring galaxy?

The Large Magellanic Cloud is a dwarf satellite galaxy of the Milky Way. Detectors on Earth caught a burst of neutrinos from the explosion two to three hours before its light arrived.

Whose name is attached to the paradox asking why the night sky is dark if stars are endless?

Heinrich Olbers described the puzzle in 1823, though he was not the first to notice it. A dark night sky is evidence that the universe has a finite age, as the Big Bang model holds.

Light from which star, brightest in the northern sky, was used to open Chicago's 1933 World's Fair?

Arcturus was chosen because its light was thought to have set out during Chicago's previous fair, in 1893. At about 37 light-years away, the estimate was only three years out.

Which star, second-brightest in the night sky, do many spacecraft use as a guide for navigation?

Canopus is brilliant and sits well away from the ecliptic, which makes it easy for a sensor to pick out. Mariner 4 was the first spacecraft to steer by it, on its way to Mars in 1964.

Which star in Perseus, nicknamed the Demon Star, dims every 2.9 days as a companion eclipses it?

Algol fades to about a third of its usual brightness for some ten hours, then recovers. It gave its name to a whole class of eclipsing variable stars.

Earth's axis wobbles like a spinning top, slowly changing which star marks north; what is this motion called?

Precession takes about 26,000 years to complete one circuit. Greek astronomers caught it more than 2,000 years ago, when star positions no longer matched older records.

Which European space observatory, shut down in 2025, spent a decade charting over a billion stars?

Gaia measured each star's position again and again, revealing its distance and its motion through the Milky Way. Work on turning the data into a 3D map of our galaxy carried on after shutdown.

Omega Centauri, long mistaken for a single star, is really which kind of ancient star group?

A globular cluster can hold millions of stars bound together by gravity, and some are among the oldest objects in the universe. Omega Centauri is bright enough to see without a telescope.

Which red dwarf, six light-years away, holds the record for the fastest drift across Earth's sky?

Barnard's Star shifts by half the width of the full Moon in a human lifetime, yet it is too faint to see without a telescope. Edward Emerson Barnard measured the record motion in 1916.

Which faint star in Draco the Dragon marked the north celestial pole nearly 5,000 years ago?

Thuban came within a sixth of a degree of the pole in 2830 BC. Earth's slowly wobbling axis has since carried the pole far away from it.

Which physicist won the 1967 Nobel Prize for working out the nuclear reactions that make stars shine?

Hans Bethe cracked the problem in 1939, showing how stars heavier than the Sun fuse hydrogen with carbon acting as a catalyst. In wartime he led the theorists building the first atomic bombs at Los Alamos.

The mass limit above which a dying star's core must collapse, about 1.4 Suns, bears whose name?

Chandrasekhar began the work in 1930, aged 19, on his way from India to study at Cambridge. NASA's Chandra X-ray Observatory is named in his honour.