49 Fun Facts About Milky Way

What type of galaxy is the Milky Way?

Barred spiral: a long bar of old stars crosses the centre instead of the arms winding right in. A 2005 infrared survey of some 30 million stars showed the bar was far longer than astronomers had thought.

Roughly how many stars is the Milky Way estimated to contain?

Between 100 and 400 billion is the usual estimate. The range is wide because we count from inside the galaxy, and its dim, low-mass stars are very hard to detect.

The Sun sits in which spiral arm of the Milky Way?

The Orion Arm, a minor spur between two larger arms. It puts us about 26,000 light-years from the centre, roughly halfway to the edge, in what NASA calls the suburbs of the galaxy.

What is the intense radio source at the Galactic Center called?

Sagittarius A*, said 'A-star', marks the galaxy's supermassive black hole. In 2022 the Event Horizon Telescope released the first image of it: a glowing ring of gas around a dark shadow.

Roughly how massive is the black hole at the centre of the Milky Way?

About 4 million solar masses, weighed by tracking stars that whip around an invisible object at the centre. That work won Reinhard Genzel and Andrea Ghez a share of the 2020 Nobel Prize in Physics.

In 1610, who first resolved the band of the Milky Way into individual stars with a telescope?

Galileo Galilei. In his 1610 booklet Sidereus Nuncius he reported that the Galaxy is 'nothing else but a mass of innumerable stars', ending centuries of dispute over what the band was made of.

Whose 1923 observations showed the Milky Way was just one galaxy among many?

Edwin Hubble found Cepheid variable stars, whose pulsing reveals their true distance, inside a spiral 'nebula'. They put it far outside the Milky Way, settling astronomy's 'Great Debate' of 1920.

Hunting static on transatlantic phone links around 1932, Karl Jansky traced a faint hiss to the Milky Way, founding which science?

Radio astronomy. The Bell Labs engineer tracked the hiss for months with a rotating antenna and found it came from a direction fixed among the stars, the heart of the Milky Way, not from storms or the Sun.

Why does the Milky Way appear as a band across the night sky?

We see its disc from inside: the galaxy is flat, so looking along it piles the stars into a band. In a ball-shaped elliptical galaxy the stars would be spread all around the sky instead.

In Greek myth, whose spilled milk formed the Milky Way?

Hera's. In the usual telling Zeus held the infant Heracles to his sleeping wife's breast to make him immortal; she woke and pushed the child away, and her milk sprayed across the sky.

In Irish, the Milky Way is called 'the Way of the White' what?

Cow: Bealach na Bó Finne. 'White cow' is also what the name of Bóinn, goddess of the Boyne, means, and the band seems to have been seen as the Boyne's reflection in the sky.

Around 1380, which English poet wrote of 'the Galaxye, which men clepeth the Milky Wey'?

Geoffrey Chaucer, in his poem The House of Fame. The English name is traced back to this line, a direct translation of the Latin via lactea, and he adds the reason himself: 'for hit is whyt'.

In Finnish, Estonian and several Turkic languages, the galaxy is named after what?

The path of migrating birds: Linnunrata in Finnish, Linnutee in Estonian. Northern peoples saw that birds heading south for the winter follow the line of the band across the sky.

What does the Chinese name for the Milky Way, used across East Asia, translate to?

Silver River. In the legend behind China's Qixi and Japan's Tanabata festivals, it is the river that parts a weaver girl from her cowherd husband, who may cross it to meet her only once a year.

Pilgrims to which holy site traditionally used the Milky Way as a guide?

Santiago de Compostela. The band seemed to point pilgrims west across Spain, so Spaniards still call the Milky Way El Camino de Santiago; one medieval legend says it was made of dust kicked up by their feet.

What does 'Vintergatan', the Swedish name for the Milky Way, mean?

Winter Street. Nobody is sure why: one idea is that the bright summer nights of the far north hide the band, so it shows best in winter; another is that people once read it to forecast the coming winter.

In an Armenian legend echoed in Arabic and Turkish names for the galaxy, a fleeing thief spilled a trail of what?

Straw: Armenians called the galaxy the Straw Thief's Way, after the god Vahagn, who stole straw from the Assyrian king Barsham one cold winter and spilled some as he fled. Turkish Samanyolu still means 'straw road'.

The Gomeroi people of Australia see the dark dust lanes of the band as which giant animal?

An emu, whose head is the dark Coalsack nebula beside the Southern Cross, with neck and body trailing along the band. When it seems to run across the sky in April and May, real emus are laying and eggs can be gathered.

What are the swarms of ancient stars that orbit in the Milky Way's halo called?

Globular clusters: tightly bound balls of up to millions of stars, among the oldest in the galaxy. Harlow Shapley mapped them in the 1910s and found they centre on a point far from the Sun, the true middle of the galaxy.

What is the dark region of the band where interstellar dust hides the stars behind called?

The Great Rift, a dark river of dust and gas clouds running along the band from Cygnus towards the galaxy's centre. Infrared light slips through the dust, so infrared telescopes can see the stars it hides.

A 2016 world atlas of light pollution ranked which country the worst, with the Milky Way hidden from every resident?

Singapore, a city-state lit from edge to edge, where eyes never fully adapt to the dark. The same atlas found the band hidden from more than a third of humanity, including nearly 80% of North Americans.

Which philosopher wrote in Meteorologica that the Milky Way was part of Earth's upper atmosphere?

Aristotle took the band for a dry vapour set alight in the upper air, below the Moon. In the same book he waved away Democritus, who had already called the milky way the light of stars.

The Drake equation, drawn up in 1961, is a way of estimating the number of what in the Milky Way?

Alien civilisations whose signals we might detect. Frank Drake wrote it as the agenda for a small 1961 meeting in West Virginia, to organise what nobody knew rather than to reach a firm number.

Which philosopher proposed in 1755 that the Milky Way is a vast rotating system of stars, and faint nebulae other such systems?

Immanuel Kant reasoned that whatever set the planets circling the Sun in a single plane could do the same for the stars. The idea of distant 'island universes' remained a guess until the 1920s, when the nebulae proved to be galaxies.

Which astronomer, the discoverer of Uranus, first tried to map the Milky Way's shape in 1785 by counting stars?

William Herschel counted the stars in patch after patch of sky with telescopes he built himself, reasoning that more stars meant a deeper galaxy. His map put the Sun near the middle, a mistake that stood for well over a century.

Which ESA spacecraft, launched in 2013, charted nearly two billion stars to build a 3D map of the Milky Way?

Gaia measured each star's position dozens of times over more than a decade, until ESA switched it off in March 2025. Tiny shifts in position give a star's distance and its motion through the galaxy.

Roughly how long does the Solar System take to complete one orbit of the galaxy, a 'galactic year'?

About 240 million years, though estimates run from roughly 220 to 250 million. Even at more than 200 km every second, the Sun has managed only about 20 laps since it formed.

Which Dutch astronomer, namesake of the distant cloud that supplies long-period comets, showed in the 1920s that the Milky Way rotates?

Jan Oort showed that stars nearer the centre overtake the Sun while those farther out fall behind, just as inner planets pass outer ones. He was still in his twenties; his comet cloud came more than two decades later.

Which insect was shown in 2013 to keep a straight course at night by the glow of the Milky Way?

The dung beetle: in a Johannesburg planetarium, beetles rolled their balls as straight under the band alone as under a full starry sky. A straight line is the fastest escape from rivals at the dung pile.

What is the other giant spiral in the Local Group besides the Milky Way?

The Andromeda Galaxy, 2.5 million light-years away, is the nearest major galaxy and can be seen with the naked eye. The light you see tonight left it long before our species existed.

In 1987, the closest supernova seen in nearly four centuries flared in which satellite galaxy of the Milky Way?

The Large Magellanic Cloud, the biggest of the Milky Way's satellite galaxies. The blast was seen on 23 February 1987, but the galaxy is so far off that the star had really died some 160,000 years earlier.

In 2009, astronomers studying a dust cloud near the galaxy's centre found a chemical that helps give which fruit its flavour?

Raspberries: the chemical is ethyl formate, which also smells of rum. It turned up during a hunt through the cloud for amino acids, the building blocks of life, that otherwise came up empty.

Debris from the Milky Way's last big merger is nicknamed after which food, for its long, thin shape on astronomers' charts?

A sausage: plotted by their speeds, stars from the wrecked smaller galaxy form a long, narrow blob. The crash, some 8 to 10 billion years ago, is thought to have built much of the Milky Way's inner bulge and outer halo.

When did a 2012 NASA forecast say the Milky Way would hit its nearest large neighbour?

In about 4 billion years, NASA said, with the stars so far apart that hardly any would actually hit. A 2025 study using newer data put the odds of any collision in the next 10 billion years at only about fifty-fifty.

Most galaxies' light is shifted red as they recede; our fast-approaching neighbour's is shifted towards which colour?

Blue: light waves from anything coming towards us are squeezed shorter, just as an approaching siren rises in pitch. The shift shows the neighbouring galaxy closing on us at about 110 km every second.

The Milky Way's outer stars orbit too fast for the gravity of its visible stars and gas, which points to what?

Dark matter: unseen mass whose gravity keeps the fast outer stars from flying off. Vera Rubin's measurements of other spiral galaxies in the 1970s made the case, and it is thought to far outweigh everything we can see.

Which telescope, named for the first nuclear reactor's builder, lent its name to gamma-ray lobes at the galactic core?

Fermi, NASA's gamma-ray telescope, which spotted the two bubbles in 2010. Each reaches 25,000 light-years from the centre, and they may be the remnant of an ancient outburst from the galaxy's central black hole.

Maps on the Pioneer and Voyager probes fix the Sun's place in the galaxy using 14 of which objects?

Pulsars: each sweeps a beam past us at its own precise rate, so the 14 timings identify them like fingerprints. Because the rates drift over the ages, a finder could also work out how long ago the probes set off.

Which infrared space telescope's 2005 survey showed the Milky Way's central bar was far longer than thought?

The Spitzer Space Telescope sees in infrared, which passes through the dust hiding the galaxy's centre from ordinary telescopes. Its count of some 30 million stars showed the bar lies at about 45 degrees to our line to the centre.

Which type of star makes up about three-quarters of all the stars in the Milky Way?

Red dwarfs: small, cool stars that burn so slowly they can last for trillions of years. Common as they are, not one is bright enough to see with the naked eye, not even our nearest neighbour, Proxima Centauri.

After hydrogen, which element makes up nearly all the rest of the gas between the Milky Way's stars?

Helium: about nine in every ten atoms of the gas are hydrogen, and nearly all the rest are helium. Thin as it is, the gas adds up to some 10 to 15% of the mass of the galaxy's stars, the raw material for new ones.

The Milky Way's starry disc is about 100,000 light-years across; roughly how thick is it?

About 1,000 light-years, a hundredth of its width, which makes the disc about as flat, in proportion, as a CD. Only the central bulge of older stars fattens the middle.

Mapped in 2014, which supercluster is home to the Milky Way?

Laniakea, 'immense heaven' in Hawaiian, a name chosen to honour the Polynesian navigators who crossed the Pacific by the stars. It holds about 100,000 galaxies, of which the Milky Way is just one.

The Sun sits inside the Local Bubble, a vast hollow in the galaxy's gas blown out by what?

Exploding stars: a run of some 15 supernovae, beginning about 14 million years ago, swept the gas outwards. A 2022 study found that nearly all the young stars near the Sun formed on the bubble's surface, from the gas it piled up.

In a common reading of the Babylonian epic Enuma Elish, the Milky Way is the tail of which slain sea deity?

Tiamat: the god Marduk splits her body in two to make the heavens and the earth, and the Tigris and Euphrates flow from her eyes. The text says only that he twisted her tail into a great cosmic bond, which many read as the Milky Way.

In 2018, a star swinging past the Milky Way's central black hole confirmed a prediction of whose theory?

Albert Einstein: as the star S2 swept past at almost 3% of the speed of light, its light was stretched to longer wavelengths, just as general relativity predicts and Newton's gravity does not.

By a 2013 estimate from Kepler data, the Milky Way may hold up to how many Earth-sized planets in habitable zones?

40 billion, counting planets around small, cool stars as well as some 11 billion around stars like the Sun. The team reckoned one Sun-like star in five has such a planet, the nearest perhaps only 12 light-years away.

What is happening to the small galaxy that has crashed through the Milky Way at least three times?

Being torn apart: the little Sagittarius galaxy has been stretched into streams of stars that loop around ours. Each crash seems to have set off a burst of star birth, one of them at about the time the Sun formed.

A 2007 study put a Milky Way star's age at 13.2 billion years using a method that works like what?

Carbon dating: the star holds radioactive uranium and thorium, which decay at a steady, known rate, so the amount left shows how long the clock has run. It reads 13.2 billion years, nearly as old as the universe itself.