99 Fun Facts About Galaxies

In the best-known Greek myth, the Milky Way is milk spilled by which goddess as she pushed Zeus's nursing infant son away?

Hera. The baby was Heracles, and her spilled milk also gave us the word galaxy, from the Greek gala, meaning milk; the Romans carried the image over as via lactea.

What type of galaxy is the Milky Way?

Barred spiral. Dust in the disc hides the core from us, so the long bar of old stars across it was only pinned down in 2005, by the Spitzer infrared telescope.

Which space telescope, launched in 2021, was built to see the universe's first galaxies in infrared light?

Webb. It works about 1.5 million kilometres from Earth behind a five-layer sunshield, because its own warmth would otherwise swamp the faint infrared glow it is hunting.

Most of the mass in a typical galaxy is in what form?

Dark matter. In 1933 Fritz Zwicky found the galaxies in one cluster moving far too fast for their visible matter to hold them together, and blamed something unseen that he called 'dunkle Materie'.

What is commonly found at the centre of a galaxy?

A supermassive black hole. Astronomers showed the Milky Way has one by tracking stars as they whip around an unseen point at its centre, work that won the 2020 Nobel Prize in Physics.

A 2016 study estimated the observable universe holds at least how many galaxies?

Two trillion. The study concluded that about 90 percent of galaxies are too faint and too far away for even Hubble to see, which put the total at ten times the earlier estimate.

Roughly how far from Earth is the Andromeda Galaxy?

2.5 million light-years. The light reaching your eye tonight left Andromeda long before modern humans existed, yet it is the nearest large galaxy and you can see it without a telescope.

The Milky Way belongs to which small association of galaxies?

The Local Group. Gravity binds its 50-plus galaxies so firmly that, while most of the universe flies apart, its two giants, the Milky Way and Andromeda, are falling toward each other.

The Milky Way's home group is part of which supercluster?

Virgo. The supercluster is named for the great cluster at its heart, but since 2014 astronomers have treated it as just one lobe of a far larger structure, mapped by the way galaxies flow.

Before the word galaxy caught on, other galaxies were popularly called what?

Island universes. The name pictured each spiral nebula as a separate system of stars marooned far outside the Milky Way, a claim astronomers fought over until the 1920s.

Which astronomer championed the word "galaxy" while Edwin Hubble stuck with "nebulae"?

Harlow Shapley. He had already redrawn our place in the cosmos once, using far-off star clusters to show that the Sun sits nowhere near the centre of the Milky Way.

Which Greek philosopher explained the Milky Way as a fiery vapour burning in Earth's upper atmosphere?

Aristotle. He filed the Milky Way with shooting stars as a kind of fire in the upper air, and brushed aside Democritus, who held that it was the light of stars.

When two galaxies collide, why do almost none of their stars actually crash into each other?

They are too far apart. If the Milky Way and Andromeda do merge, the Sun should come through untouched but end up on a new orbit, probably much farther from the core.

Who proved in 1610 that the Milky Way is made of countless faint stars?

Galileo Galilei. Through his new telescope the hazy band broke up into countless separate stars, and within weeks he had rushed the news into print in a booklet called the Starry Messenger.

Which German philosopher argued in 1755 that the Milky Way is one of many discs of stars?

Immanuel Kant. He took the disc idea from a review of a book by the English astronomer Thomas Wright, then guessed that faint smudges in the sky were other Milky Ways, 170 years before anyone could prove it.

Who first mapped the Milky Way's shape in 1785 by counting stars in different directions?

William Herschel. Counting with his sister Caroline, he got the disc shape right but put the Sun near the hub, because dust hid all but the nearest few thousand light-years of stars.

Besides Andromeda, which spiral galaxy can keen eyes spot without a telescope under very dark skies?

Triangulum. Its glow is spread so thin that a little light pollution wipes it out, which is why stargazers use spotting it as a test of a truly dark sky.

The two small companion galaxies that light up southern skies are named after which explorer?

Ferdinand Magellan. Neither he nor his voyage's chronicler, who described the pair around 1520, gave them the name; it spread among sailors and took centuries to reach the science books.

Charles Messier catalogued fuzzy sky objects because they kept being mistaken for what?

Comets. Messier hunted them for a living and listed the look-alikes as nuisances to skip, yet that list of things to ignore is what made his name.

In 1845 Lord Rosse used the world's largest telescope to make the first drawing of spiral arms in which galaxy?

Whirlpool. Rosse sketched its spiral by hand at the eyepiece of the 72-inch giant he had built on his Irish estate, a telescope that stayed the world's largest for some seventy years.

Beginning in 1912, Vesto Slipher found the light of most spiral nebulae shifted toward which colour, a sign they were racing away?

Red. A few close neighbours broke the pattern, Andromeda among them: their light is shifted the other way, toward blue, because they are falling toward us.

Why do the arms of a spiral galaxy look bluer than its central bulge?

They hold young, hot stars. New stars form in the gas-rich arms, and the hottest, bluest of them die young, so the bulge, where star birth stopped long ago, is left with a warmer, yellowish glow.

Which variable stars let Edwin Hubble measure distances to the spiral nebulae?

Cepheids. The slower one of these stars pulses, the brighter it truly is, a rule found by Henrietta Leavitt, so comparing true with apparent brightness gave Hubble the distance.

Radio telescopes map the Milky Way's dust-hidden spiral arms using a famous hydrogen signal at which wavelength?

21 cm. Radio waves of that length pass straight through the dust that blocks starlight, so the signal gave astronomers their first real map of the Milky Way's spiral arms.

Whose 1970s work on galaxy rotation speeds pointed to large amounts of unseen mass?

Vera Rubin. She found stars at the outer edge of spiral galaxies moving so fast they should fly off into space, unless far more material than anyone could see was holding them in.

Hubble's director spent ten days in 1995 staring at what?

A blank patch of sky. Doubters had predicted Hubble would see nothing new so far out, but the tiny speck in Ursa Major came back crowded with roughly 3,000 galaxies.

Edwin Hubble's famous diagram sorting galaxies by shape is nicknamed after which everyday object?

A tuning fork. Ellipticals line up along the handle, and the diagram then splits into two prongs because spirals come in two families, those with a central bar and those without.

The largest known galaxies sit where?

At a cluster's centre. Sitting where neighbours fall in, these giant ellipticals grow by swallowing them, and many still show several bright cores, the remains of their victims.

Roughly how long does the Sun take to circle the centre of the Milky Way once?

230 million years. One lap is called a galactic year, and it takes that long even though the Solar System is covering it at about 828,000 kilometres an hour.

A spiral galaxy with poorly defined, patchy arms is called what?

Flocculent. The word means woolly, a nod to arms that break up into fluffy tufts of stars instead of the long, sweeping lanes of what astronomers call a grand design spiral.

Spiral arms are thought to be what kind of phenomenon?

Density waves. The arms are patterns, not fixed bands of stars: stars and gas drift in and out of them like cars through a traffic jam, which is why the arms don't simply wind themselves up.

Roughly how many stars does the Milky Way contain?

200 billion. It is only a rough midpoint: from inside the disc nobody can count them, so astronomers weigh the galaxy instead, and their estimates run from 100 to 400 billion.

A ring galaxy is thought to form when what happens?

A small companion punches through a spiral's core. The shock spreads outward like ripples from a stone dropped in a pond, lighting a ring of new stars, as in the Cartwheel Galaxy.

Which galaxy type has a spiral's disc but no arms?

Lenticular. One idea is that these are spirals grown old, in which star birth has all but stopped and the arms have simply faded from view.

Which small galaxy, found in 1994 beyond the Milky Way's centre, is our galaxy swallowing?

Sagittarius Dwarf. Hidden on the far side of the Milky Way's crowded centre, it went unnoticed until 1994, by which time our galaxy's gravity had already stretched it into a long smear of stars.

Why can't a starburst galaxy keep forming stars so fast for long?

Its gas runs out. A starburst turns gas into stars so fast that it would burn through its whole supply in a sliver of the galaxy's lifetime, so the frenzy can only ever be a passing phase.

What triggered the Cigar Galaxy's frenzy of star birth?

A neighbour's pull. A close encounter with its bigger neighbour M81 is thought to have stirred the Cigar's gas into making stars, and its centre now turns them out ten times faster than the whole Milky Way.

Which objects, first mistaken for faint blue stars, turned out to be the blazing cores of very distant galaxies?

Quasars. The name comes from quasi-stellar, or star-like: on photographs they looked like ordinary stars, until their light proved to have crossed billions of light-years, so each had to outshine a whole galaxy.

Which Christmas film classic opens with talking angels shown as the galaxy group Stephan's Quintet?

It's a Wonderful Life. Its heavenly narrators appear as the blinking galaxies of Stephan's Quintet, though only four of the five are really neighbours; the fifth just happens to lie in front.

Lower-luminosity active galactic nuclei are known as what kind of galaxies?

Seyfert. Carl Seyfert picked them out in 1943: in ordinary light they pass for normal spirals, but at other wavelengths the tiny core alone can rival the output of all the galaxy's stars.

A blazar is an active galaxy whose relativistic jet is doing what?

Pointing at Earth. Staring almost straight down the barrel of the jet makes it look far brighter and more changeable than the same kind of galaxy would if we saw it from the side.

What do astronomers call the vast, nearly empty gaps between the filaments of the cosmic web?

Voids. Gravity has spent billions of years drawing matter out of these emptier regions and into threads and sheets, leaving bubbles some 150 million light-years across with very few galaxies inside.

Which name did astronomers give in 2014 to the Milky Way's home supercluster?

Laniakea. The name is Hawaiian for 'immense heaven', chosen to honour the Polynesian navigators who crossed the Pacific by reading the stars.

Which ancient swarms of hundreds of thousands of stars orbit in the halo around a galaxy's disc?

Globular clusters. Their stars are among the oldest known, and plotting where the clusters lie is how astronomers first worked out where the centre of the Milky Way is.

Which European space telescope mapped the positions and motions of nearly two billion Milky Way stars between 2014 and 2025?

Gaia. Among the stars it tracked was a swarm moving the wrong way around the galaxy, the wreckage of a large galaxy the Milky Way swallowed about ten billion years ago.

The first stars were made almost entirely of which two elements?

Hydrogen and helium. Almost nothing heavier existed yet, because elements such as carbon, oxygen and iron are forged inside stars; astronomers call that first generation Population III.

The period after recombination and before the first stars is called what?

The dark ages. No star had yet formed and the gas filling space soaked up light, so the cosmos stayed black until gravity squeezed the first clumps of gas hot enough to ignite.

Which stars burn their fuel so slowly that they will be the last still shining, trillions of years from now?

Red dwarfs. The smallest stars sip their fuel so slowly that not one has ever died of old age: at 13.8 billion years, the cosmos is far too young.

The colliding Antennae Galaxies are named for which feature of the pair?

Tidal tails. The collision flung out two long streamers of stars that curve away like an insect's feelers, while the crash itself is lighting up billions of new stars.

A dust cloud near the Milky Way's centre holds a chemical that flavours raspberries and smells of which drink?

Rum is the smell of ethyl formate, a chemical that also helps give raspberries their taste. A radio telescope picked it out among some 50 molecules found in the cloud.

In the film Men in Black, the miniature galaxy everyone is hunting hangs from the collar of which animal?

A cat wore the galaxy on its collar all along. A dying alien's clue about a belt referred to the pet's name, borrowed from a constellation, and not to the stars themselves.

Which galaxy, Messier 104, is nicknamed after a hat because a dark dust lane rims its bright bulge?

Sombrero is the nickname of a galaxy seen almost edge-on, about 31 million light-years away. Its glowing bulge makes the crown of the hat and the dust lane the brim.

A 2016 study found a third of humanity can no longer see the Milky Way because of which problem?

Light pollution from towns and cities hides the band from 80% of Americans and 60% of Europeans. Under truly dark skies the Milky Way is bright enough to cast a shadow.

Which Greek hero rescued the chained princess whose name now belongs to the Milky Way's nearest major galaxy?

Perseus killed the sea monster sent to devour Andromeda, then married her. The pair now sit side by side as constellations, and the galaxy is named after hers.

Aboriginal Australians trace which bird in the dark dust clouds that run along the Milky Way?

An emu stretches along the band, with the Coalsack Nebula beside the Southern Cross as its head. The figure is drawn from the dark gaps in the glow and not from stars.

The Hubble Space Telescope needed corrective optics in 1993 because which part was made to the wrong shape?

Its main mirror was too flat at the outer edge by about 2,200 nanometres, enough to blur every image. The repair added optics with the opposite error, working like a pair of spectacles.

What nickname have astronomers given the giant galaxy that may form if the Milky Way and Andromeda merge?

Milkomeda blends the two galaxies' names. A 2025 study made the crash far from certain, giving only about an even chance of a head-on merger in the next 10 billion years.

Many Indian languages name the Milky Way after which sacred river, imagined as flowing across the sky?

The Ganges gives the galaxy its Sanskrit name, Akasaganga, the river of the sky. Finns call the same band the Pathway of the Birds, after the migrating flocks thought to follow it south.

Despite its name, the light-year that astronomers use to describe galaxies is a unit of which quantity?

Length is what a light-year measures: the span light crosses in a year, about 63,000 times the gap between Earth and the Sun. The word year tempts many people into treating it as a stretch of time.

Which force holds a galaxy's stars, gas and dust together as a single system across thousands of light-years?

Gravity binds every galaxy, and it also ties galaxies to one another, gathering them into families hundreds or even thousands strong.

Which star system, a little over four light-years away, lies closest to the Sun in the Milky Way?

Alpha Centauri is really three stars, and the faintest of them, Proxima, is the closest of all at about 4.2 light-years. Seen together they rank third-brightest in the night sky.

When a massive galaxy bends the light of a more distant one into a circle, the ring is named after which physicist?

Albert Einstein predicted that mass bends light, but another physicist, Orest Khvolson, first wrote about the ring itself in 1924. It needs both galaxies and the observer lined up almost perfectly.

In a Cherokee folktale, the Milky Way is a trail of cornmeal spilled by which thieving animal?

A dog stole the cornmeal and was chased away, spilling it across the sky as it fled north. The Cherokee name for the band means the place where the animal ran.

Which desert, the driest outside the poles, hosts many of the giant telescopes that study distant galaxies?

The Atacama in Chile pairs high altitude and dry air with more than 200 cloudless nights a year. The Very Large Telescope is among the observatories built there.

Astronomers clock how fast a galaxy approaches or recedes using which phenomenon, also heard in a passing siren?

The Doppler effect stretches the light of a retreating galaxy to longer wavelengths and squeezes it for an approaching one. Christian Doppler described the idea in 1842, long before other galaxies were known.

The Milky Way appears as a pale band across the night sky because Earth views the galaxy's disc from where?

From inside it, the flat disc of stars surrounds Earth, so its combined glow wraps the whole sky like a ribbon. Every star visible to the naked eye belongs to the same galaxy.

In the Chinese tale of the cowherd and weaver girl, lovers parted by the Milky Way cross a bridge of which birds?

Magpies flock together once a year, on the seventh day of the seventh lunar month, to span the river of stars. China's Queqiao relay satellites are named after that bridge.

A supernova that flared in the Milky Way in 1604, visible to the naked eye, is named after which astronomer?

Johannes Kepler described the new star in a book, De Stella Nova. At its peak it outshone every other star in the night sky.

Which space shuttle carried the Hubble Space Telescope into orbit in April 1990?

Discovery carried Hubble up seven years after its intended 1983 launch. Technical delays, budget trouble and the 1986 Challenger disaster had all held the telescope back.

The giant telescope that first revealed a galaxy's spiral arms in 1845 stood on an earl's estate in which country?

Ireland was home to the Leviathan of Parsonstown, built at Birr Castle by the Earl of Rosse. The 72-inch reflector stayed the largest telescope in the world until 1917.

Astronomers voted in 2018 to rename Hubble's law on receding galaxies to share credit with which Belgian priest?

Georges Lemaître published the link between a galaxy's distance and its speed in 1927, two years before Hubble. His paper was published in French in a low-impact journal.

Which Harvard astronomer linked a pulsing star's rhythm to its true brightness, unlocking the distances to galaxies?

Henrietta Leavitt found the pattern while measuring photographic plates as a human computer at the Harvard observatory. Before her, star distances could only be gauged by parallax.

The Solar System sits near the inner rim of which spiral arm of the Milky Way, some 3,500 light-years wide?

The Orion Arm was once dismissed as a minor spur between two larger arms. Evidence presented in 2013 suggests it may be a branch of a major arm or an arm segment in its own right.

The English name Milky Way can be traced back to a story of about 1380 by which poet?

Geoffrey Chaucer used the name in The House of Fame, a dream poem in which a golden eagle seizes the narrator and lifts him up into the sky.

Which Greek thinker, famed for his theory of atoms, held that the Milky Way was the glow of certain stars?

Democritus shared the view with Anaxagoras some 2,000 years before a telescope showed the band's separate stars. They thought those stars lay hidden in the shadow cast by the Earth.

Astronomers gauging how far away a galaxy lies rely on objects of known true brightness, each called a standard what?

Candle is the word because the method works like judging how far off a flame is by how dim it looks. Exploding stars of one particular type serve for the most remote galaxies.

The face-on spiral Messier 101, found in Ursa Major in 1781, is popularly known as which galaxy?

The Pinwheel suits a spiral seen almost exactly face-on. Its finder, Pierre Méchain, passed it to Charles Messier, who made it one of the final entries on his famous list.

Edwin Hubble made his great galaxy finds of the 1920s with the 100-inch Hooker Telescope on which California mountain?

Mount Wilson held the world's largest telescope from 1917 to 1949. The same air layer that traps smog over Los Angeles gives the peak some of the steadiest skies in North America.

Galaxy Zoo volunteers sorted nearly a million galaxies photographed from New Mexico by which mapping project?

Sloan Digital Sky Survey images were too many for one astronomer, who classified 50,000 by eye in a week and found it mind-numbing. Over 100,000 volunteers then did the job in about 175 days.

In galaxy names such as NGC 1300, the letters NGC stand for which 1888 list of deep-sky objects?

New General Catalogue was compiled by John Dreyer and lists 7,840 objects. His two later supplements, the Index Catalogues, are why thousands more galaxies carry IC numbers.

The Milky Way's north pole lies in a constellation, rich in galaxies, named after which Egyptian queen's hair?

Berenice II vowed to cut off her long hair if her husband came home safely from war. Hers is the only modern constellation named after a historical person.

Which Swiss astronomer found in 1933 that galaxies crowded together in Coma move too fast for their stars to hold them?

Fritz Zwicky also coined the word supernova with Walter Baade, and the pair were the first to propose that such explosions leave neutron stars behind.

Which Bell Labs engineer, hunting for static on phone links in the 1930s, found radio noise coming from the Milky Way?

Karl Jansky caught the hiss with an antenna that turned on four Ford Model T wheels, nicknamed his merry-go-round. The unit radio astronomers use for a signal's strength is named after him.

Vesto Slipher first clocked the speeds of galaxies at which Arizona observatory, where Pluto was later found?

Lowell Observatory in Flagstaff took Slipher on as a temporary assistant in 1901. He rose to become its director and hired Clyde Tombaugh, the young man who spotted Pluto.

Galaxy distances come from a chain of methods, each calibrating the next, known as the cosmic distance what?

Ladder is the image because no single technique works at every range, so each rung is used to set up the next one out. Only the lowest rungs measure distances directly.

What do astronomers call the thin gas and dust spread through a galaxy, the raw material from which new stars form?

The interstellar medium is thinner than the best laboratory vacuum, yet there is enough of it to keep building stars. In the Milky Way it is 99% gas and 1% dust by mass.

Which nickname does the spiral galaxy Messier 64 owe to a dark band of dust lying across its bright nucleus?

The Black Eye holds a stranger secret: its outer gas circles the opposite way to the gas nearer the middle, perhaps because it once swallowed a gas-rich satellite galaxy.

Which NASA space telescope, launched by shuttle in 1999, studies galaxies and exploded stars in X-rays?

Chandra can pick up X-ray objects 100 times fainter than any earlier telescope could. Its name, chosen in a public contest, honours the astrophysicist Subrahmanyan Chandrasekhar.

In the Great Debate of 1920, which astronomer rightly argued that spiral nebulae were galaxies far beyond our own?

Heber Curtis was proved right on the central question within a few years. He and his opponent each gave a 40-minute lecture at what is now the Smithsonian's natural history museum.

Which astronomer, Edwin Hubble's partner in clocking galaxy speeds, began as a mule driver and observatory janitor?

Milton Humason left school at 14 and hauled supplies up the mountain by mule while the observatory was being built. He joined the scientific staff without even a high school diploma.

Which Dutch astronomer showed that the Milky Way rotates, with stars nearer its middle overtaking those farther out?

Jan Oort compared the stars to planets, where those nearer the Sun overtake those farther out. A vast shell of icy bodies at the edge of the Solar System also carries his name.

Which Persian astronomer described the Andromeda Galaxy as a small cloud in his Book of Fixed Stars around 964?

Al-Sufi saw it with the naked eye, more than six centuries before the telescope. It is the earliest recorded observation of that galaxy, in a book charting all 48 classical constellations.

The bright spiral Messier 81 in Ursa Major is popularly named after which German astronomer, who found it in 1774?

Johann Bode spotted it on the last night of 1774, years before Charles Messier added it to his own list. It is the largest of a family of 34 galaxies.

The giant gamma-ray bubbles above and below the Milky Way's centre are named after which NASA space telescope?

Fermi data revealed the two lobes in 2010, each reaching about 25,000 light-years from the galactic centre. The team that found them won a prize for a structure nobody had anticipated.

Dust in the Milky Way's plane hides a fifth of the distant sky in a strip called the Zone of what?

Avoidance is the word because galaxies seemed to shun the strip, which an 1878 paper first called the Zone of Few Nebulae. Radio telescopes can see straight through it.

A Dutch schoolteacher sorting galaxy images as a volunteer in 2007 found a glowing green cloud now called Hanny's what?

Voorwerp is simply Dutch for object, a sign of how baffling it was. The cloud is about as big as a small galaxy and has a gap 16,000 light-years across in its middle.

Astronomers who averaged the light of over 200,000 galaxies named the universe's colour after which coffee drink?

Latte won out even though cappuccino got more votes in the naming poll. The team had first announced a pale green, then found a software error weeks later and arrived at beige.

Which comedy troupe's 1983 film features the Galaxy Song, a musical tour of the Milky Way's size and speed?

Monty Python's Eric Idle sings it after stepping out of a refrigerator. Most of the astronomical figures in the song are accurate to within one or two significant figures.

Which European space telescope, launched in 2023, was built to chart galaxies in 3D across a third of the sky?

Euclid looks at galaxies as they were up to 10 billion years ago, tracing how the expansion of the universe has changed. Its name honours the ancient Greek mathematician.