How every fact on this site was checked
115 facts. Each one is in our own words, each one has a source, and each one was checked against that source on 13 November 2026.
How we check
We read each source and wrote each fact in our own words. Our build stores the text of every source page, and for each fact it checks that the key words and figures, the “checks” in the table, really appear on the source page. If any check fails, the site does not build. Where good sources disagree, we show each version in a “Sources differ” box rather than picking one. Anything that is our own reading, rather than a sourced fact, is labelled Our opinion. The drawings are our own and simplified.
Known disagreements
- Distance. 2.5 million light-years (NASA), about 2,480,000 (Britannica) or about 2 million (the Royal Observatory’s closest-galaxy page).
- Width. About 152,000 light-years (Royal Observatory), approximately 200,000 (Britannica) or some 220,000 (NASA).
- Size in the sky. Six times as wide as the full Moon (NASA’s Messier 31 page), roughly the size of the full Moon to the naked eye (NASA, 2025), or about 3 by 1 degrees, twice the Moon’s width (EarthSky).
- Bigger than the Milky Way. As much as twice as massive (NASA) or more than twice as many stars (Royal Observatory).
- Brightness. Magnitude 3.1 (NASA) or 3.5 (EarthSky).
- How lopsided the satellites are. Seen in 0.3% of similar simulated systems (Nature Astronomy summary) or 0.1% after removing look-alikes (Sky & Telescope).
- Meeting the Milky Way. A head-on collision in about four billion years (NASA, 2012), or only a 50-50 chance in ten billion years, with about 2% for a head-on hit in 4 to 5 billion years (NASA, 2025).
What we left out
- Some popular figures, such as exact star counts or a precise width, did not appear in the sources we could check, so we give the sources’ own figures.
- Hubble’s own plate is described from NASA’s account; our drawing is a sketch of the idea, not a copy.
- Estimates such as the chance of a collision, or how unusual the satellites are, change as new data arrive. We give them as the named source states them, on the date we checked.
- The approach meter is our own arithmetic from the Royal Observatory’s and NASA’s figures, not a quoted fact.
The log
| # | Fact | Source | Checks |
|---|---|---|---|
| 1 | The Andromeda Galaxy, also called M31, is the nearest major galaxy to our own Milky Way. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 2 | It is a spiral galaxy in the constellation Andromeda. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 3 | Britannica lists its other names: the Andromeda Nebula, M31 and NGC 224. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 4 | It shares various characteristics with the Milky Way. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 5 | Astronomers use it as a stand-in for spiral galaxies in general: we would know much less about our own spiral if we did not have Andromeda to study. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 2 passed |
| 6 | NASA says studying the Milky Way from inside is like trying to understand the layout of New York City while standing in the middle of Central Park. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 7 | We see Andromeda almost edge on, tilted by 77 degrees. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 8 | NASA says Andromeda is as much as twice as massive as the Milky Way. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 1 passed |
| 9 | The Royal Observatory says it has more than twice as many stars as the Milky Way. | Royal Museums Greenwich: A guide to the Milky Way, our home galaxy (Jake Foster, Royal Observatory) | 1 passed |
| 10 | The Milky Way, Andromeda and more than 50 other galaxies make up the Local Group. | NASA Science: Galaxies | 1 passed |
| 11 | NASA gives its distance as 2.5 million light-years. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 12 | Britannica says about 2,480,000 light-years from Earth. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 13 | The Royal Observatory’s ‘closest galaxy’ page says about 2 million light-years. | Royal Museums Greenwich: What is our closest galaxy? | 1 passed |
| 14 | So the light we see left Andromeda 2.5 million years ago: we see it as it was then. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |
| 15 | Royal Observatory: about 152,000 light-years wide. | Royal Museums Greenwich: A guide to the Milky Way, our home galaxy (Jake Foster, Royal Observatory) | 1 passed |
| 16 | Britannica: approximately 200,000 light-years across. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 17 | NASA: some 220,000 light-years across. | NASA Science: Our Milky Way Galaxy: How big is space? | 1 passed |
| 18 | It is so close that it looks six times as wide as the full Moon in the sky. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 19 | NASA’s 2025 satellite story says it appears to the naked eye roughly the size of the full Moon. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 1 passed |
| 20 | EarthSky says it stretches about 3 degrees by 1 degree, twice as wide as the full Moon. | EarthSky: The constellation Andromeda the Chained Lady | 2 passed |
| 21 | ESA/Hubble says the whole galaxy contains over one thousand billion stars: more than a trillion. | ESA/Hubble heic1502: Hubble’s high-definition panoramic view of the Andromeda Galaxy (5 January 2015) | 1 passed |
| 22 | Andromeda is getting about 110 km (70 miles) closer to us every second. | Royal Museums Greenwich: A guide to the Milky Way, our home galaxy (Jake Foster, Royal Observatory) | 1 passed |
| 23 | NASA put its approach at about 250,000 miles per hour, fast enough to get from here to the Moon in an hour. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 2 passed |
| 24 | That speed was measured with the Doppler effect: Andromeda’s motion towards us squashes the waves of its starlight. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 2 passed |
| 25 | It was mentioned as early as 965 CE in the Book of the Fixed Stars by the Islamic astronomer al-Ṣūfī. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 26 | It was rediscovered in 1612, soon after the telescope was invented, by the German astronomer Simon Marius. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 27 | Marius said it looked like the light of a candle seen through a horn. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 28 | For centuries astronomers thought it was part of the Milky Way, a ‘spiral nebula’, hence the old name Andromeda Nebula. | Encyclopaedia Britannica: Andromeda Galaxy | 2 passed |
| 29 | In the early 1900s most astronomers thought the Milky Way was a single ‘island universe’ with nothing observable beyond it. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 30 | Andromeda was catalogued as just one of many faint, fuzzy ‘spiral nebulae’. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 31 | As far back as 1912, astronomers realised Andromeda, then thought to be only a nebula, was heading our way. | NASA Science: Apocalypse when? Hubble casts doubt on certainty of galactic collision (2 June 2025) | 1 passed |
| 32 | On the night of 5 October 1923 Edwin Hubble began an observing run that lasted into the early hours of 6 October. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 33 | In poor conditions he made a 45-minute exposure and marked three suspected novae, exploding stars, with an ‘N’. | NASA Science: Hubble views the star that changed the universe (2011) | 2 passed |
| 34 | Comparing that plate with older ones, he found one ‘nova’ dimmed and brightened far faster than a nova should. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 35 | He crossed out the ‘N’ and wrote ‘VAR!’, for variable, with an exclamation mark. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 36 | The star, Hubble variable number one or V1, is a Cepheid variable in Andromeda’s outer regions. | NASA Science: Hubble views the star that changed the universe (2011) | 2 passed |
| 37 | A Cepheid brightens and fades in a regular pattern, like a lighthouse, and was already known to be a reliable distance marker. | NASA Science: Hubble views the star that changed the universe (2011) | 2 passed |
| 38 | V1 showed that Andromeda lies beyond our galaxy, and settled the debate about the spiral nebulae. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 39 | Harlow Shapley, who believed the nebulae were part of the Milky Way, reportedly said of Hubble’s letter: “Here is the letter that destroyed my universe.” | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 40 | By the end of 1924 Hubble had found 36 variable stars in Andromeda, 12 of them Cepheids. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 41 | From them he worked out a distance of 900,000 light-years; better measurements later moved it to about 2 million. | NASA Science: Hubble views the star that changed the universe (2011) | 2 passed |
| 42 | Britannica: only in the 1920s did Hubble show conclusively that Andromeda is a separate galaxy. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 43 | An astronomer at the Space Telescope Science Institute called V1 “the most important star in the history of cosmology”. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 44 | In 2010 and 2011 amateur astronomers tracked V1 and the Hubble Space Telescope photographed it again, as a tribute. | NASA Science: Hubble views the star that changed the universe (2011) | 3 passed |
| 45 | V1 takes a little over 31 days to brighten and fade once. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 46 | Cepheids are still the first rung on the ‘cosmic distance ladder’ astronomers use for far more distant galaxies. | NASA Science: Hubble views the star that changed the universe (2011) | 1 passed |
| 47 | NASA says Edwin Hubble measured Andromeda’s vast distance by finding a variable star that served as a ‘milepost marker’. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 1 passed |
| 48 | In January 2015 Hubble released a 1.5-billion-pixel mosaic of part of Andromeda, showing over 100 million stars. | ESA/Hubble heic1502: Hubble’s high-definition panoramic view of the Andromeda Galaxy (5 January 2015) | 3 passed |
| 49 | Showing that 2015 image at full size would take more than 600 HD television screens. | ESA/Hubble heic1502: Hubble’s high-definition panoramic view of the Andromeda Galaxy (5 January 2015) | 1 passed |
| 50 | NASA likened resolving single stars at that distance to photographing a beach and seeing individual grains of sand. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 51 | In January 2025 Hubble released an even bigger panorama: about 2.5 billion pixels and 200 million stars. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 3 passed |
| 52 | It took over 10 years and more than 600 overlapping Hubble snapshots. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 53 | It needed over 1,000 Hubble orbits. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 54 | Even 200 million stars is only a fraction of Andromeda’s population. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 55 | Cooler, yellowish stars crowd the centre; a blue ring of young stars and star-forming regions marks a spiral arm. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 3 passed |
| 56 | The dark silhouettes in the pictures are complex lanes of dust. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 57 | NGC 206 is the most conspicuous star cloud in Andromeda. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 58 | Some bright ‘stars’ in Hubble’s picture are photo-bombers in our own Milky Way, much closer to us. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 59 | There is a supermassive black hole at Andromeda’s heart. | NASA Science: Hubble finds mysterious disk of blue stars around black hole (2005) | 1 passed |
| 60 | In 2005 Hubble measurements put its mass at 140 million Suns, three times more than once thought. | NASA Science: Hubble finds mysterious disk of blue stars around black hole (2005) | 1 passed |
| 61 | A disc of hot, young blue stars whips round the black hole, rather like planets round the Sun. | NASA Science: Hubble finds mysterious disk of blue stars around black hole (2005) | 2 passed |
| 62 | What looked like a double centre is a ring of old red stars about five light-years from the black hole. | NASA Science: Hubble finds mysterious disk of blue stars around black hole (2005) | 2 passed |
| 63 | Andromeda has a past of collisions, swallowing smaller galaxies. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 64 | Deep surveys of its outskirts show huge streams and clouds of stars, the remains of smaller galaxies it has ‘eaten’. | Encyclopaedia Britannica: Andromeda Galaxy | 2 passed |
| 65 | In 2018 University of Michigan scientists concluded that Andromeda shredded a massive galaxy, now called M32p, about two billion years ago. | University of Michigan News: The Milky Way’s long-lost sibling finally found (23 July 2018) | 2 passed |
| 66 | M32p would have been the third-largest galaxy in the Local Group, after the Milky Way and Andromeda. | University of Michigan News: The Milky Way’s long-lost sibling finally found (23 July 2018) | 1 passed |
| 67 | It was at least 20 times larger than any galaxy that ever merged with the Milky Way. | University of Michigan News: The Milky Way’s long-lost sibling finally found (23 July 2018) | 1 passed |
| 68 | They suggest the dense little galaxy M32 is its surviving centre, like the pit of a plum. | University of Michigan News: The Milky Way’s long-lost sibling finally found (23 July 2018) | 1 passed |
| 69 | One of the scientists, Eric Bell, said: “M32 is a weirdo.” | University of Michigan News: The Milky Way’s long-lost sibling finally found (23 July 2018) | 1 passed |
| 70 | NASA says the Milky Way has been relatively placid, but Andromeda has had a more dynamic history, probably including a major merger a few billion years ago. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 2 passed |
| 71 | Hubble has studied the whole known population of 36 small satellite galaxies orbiting Andromeda. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 1 passed |
| 72 | The survey built a 3D map of the dwarfs and worked out how they formed stars over nearly 14 billion years. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 2 passed |
| 73 | Half of them seem confined to one plane, all orbiting in the same direction. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 1 passed |
| 74 | One researcher, Daniel Weisz, called that “weird”: a total surprise nobody fully understands yet. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 1 passed |
| 75 | The brightest companion is M32, a compact galaxy that may be the leftover core of a larger galaxy that hit Andromeda a few billion years ago. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 2 passed |
| 76 | Many of Andromeda’s dwarfs kept forming stars slowly for far longer than expected, something computer simulations don’t show. | NASA Science: NASA’s Hubble provides bird’s-eye view of Andromeda galaxy’s ecosystem (27 February 2025) | 2 passed |
| 77 | Britannica’s pictures show M110, an elliptical galaxy that is another satellite of Andromeda. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 78 | The Royal Observatory says its two dwarf elliptical satellites can be seen with a small telescope. | Royal Museums Greenwich: What is our closest galaxy? | 1 passed |
| 79 | Most of Andromeda’s dwarf galaxies lie on our side, between Andromeda and the Milky Way, and better distances show that lopsidedness is real. | Sky & Telescope: Why are most of Andromeda’s dwarf galaxies on our side? | 2 passed |
| 80 | A 2025 Nature Astronomy summary says that degree of lopsidedness turns up in only 0.3% of similar simulated systems. | Nature Astronomy: Andromeda’s lopsided galaxy system challenges standard cosmology (11 April 2025) | 1 passed |
| 81 | Sky & Telescope reports that, after removing look-alike cases, only 0.1% of simulated galaxies were as lopsided as Andromeda. | Sky & Telescope: Why are most of Andromeda’s dwarf galaxies on our side? | 1 passed |
| 82 | The researchers say this needs either a very unusual history, or may hint that our standard picture of the cosmos is missing something. | Sky & Telescope: Why are most of Andromeda’s dwarf galaxies on our side? | 1 passed |
| 83 | The Triangulum galaxy, M33, is a smaller companion at a similar distance, and much harder to see. | Royal Museums Greenwich: What is our closest galaxy? | 1 passed |
| 84 | In 2012 NASA said Hubble measurements predicted a head-on meeting with Andromeda in about four billion years. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 1 passed |
| 85 | NASA said the Sun would probably be flung into a new part of the galaxy, but Earth and the solar system would not be destroyed. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 1 passed |
| 86 | In that picture the two would merge into a single elliptical galaxy about two billion years after the first encounter. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 2 passed |
| 87 | Stars are so far apart that they would not hit each other. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 1 passed |
| 88 | NASA’s illustrations showed Andromeda filling the night sky in 3.75 billion years, and the sky ablaze with new stars at 3.85 billion. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 2 passed |
| 89 | Triangulum would join in and might later merge with the pair; there was a small chance it would hit the Milky Way first. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 2 passed |
| 90 | In 2025 a new study using Hubble and Gaia data found only about a 50-50 chance of the two galaxies colliding in the next 10 billion years. | NASA Science: Apocalypse when? Hubble casts doubt on certainty of galactic collision (2 June 2025) | 1 passed |
| 91 | It left only about a 2% chance of a head-on collision in just 4 to 5 billion years. | NASA Science: Apocalypse when? Hubble casts doubt on certainty of galactic collision (2 June 2025) | 1 passed |
| 92 | The team considered 22 variables and ran 100,000 computer simulations reaching 10 billion years ahead. | NASA Science: Apocalypse when? Hubble casts doubt on certainty of galactic collision (2 June 2025) | 2 passed |
| 93 | Lead author Till Sawala said the two could still go past each other. | NASA Science: Apocalypse when? Hubble casts doubt on certainty of galactic collision (2 June 2025) | 1 passed |
| 94 | The Large Magellanic Cloud can change the Milky Way’s path and make a collision less likely. | ESA/Hubble heic2508: Hubble casts doubt on certainty of galactic collision (2 June 2025) | 1 passed |
| 95 | NASA points out that a warming Sun will make Earth uninhabitable in roughly a billion years, so Andromeda is the least of our cosmic worries. | NASA Science: Apocalypse when? Hubble casts doubt on certainty of galactic collision (2 June 2025) | 2 passed |
| 96 | The merged galaxy has been unofficially nicknamed Milkomeda. | Royal Museums Greenwich: A guide to the Milky Way, our home galaxy (Jake Foster, Royal Observatory) | 1 passed |
| 97 | Hubble’s deep views show galaxy collisions were more common in the past, when the universe was smaller. | NASA Science: NASA’s Hubble shows Milky Way is destined for head-on collision (31 May 2012) | 1 passed |
| 98 | It is one of the few galaxies you can see with your eyes alone, as a milky blur. | Encyclopaedia Britannica: Andromeda Galaxy | 1 passed |
| 99 | On clear, dark nights it shows faintly as a hazy patch; binoculars or a small telescope reveal its bright core and glow. | Royal Museums Greenwich: Night sky highlights, February 2026 | 1 passed |
| 100 | Through binoculars it looks like a lens-shaped smudge. | Royal Museums Greenwich: What is our closest galaxy? | 1 passed |
| 101 | Give your eyes 15 minutes to adapt to the dark, and don’t look at your phone. | Royal Museums Greenwich: Night sky highlights, February 2026 | 1 passed |
| 102 | If you use a star app, switch on its red night-vision mode. | Royal Museums Greenwich: Night sky highlights, February 2026 | 1 passed |
| 103 | The W-shaped constellation Cassiopeia points towards Andromeda. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |
| 104 | Use the right-hand V of the W as an arrow: the galaxy is a little over 15 degrees from its tip, and a bit to the right. | EarthSky: The constellation Andromeda the Chained Lady | 3 passed |
| 105 | 15 degrees is about the span of your index finger to little finger, held at arm’s length. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |
| 106 | Andromeda the constellation sits next to the Great Square of Pegasus; one of the square’s stars belongs to it. | EarthSky: The constellation Andromeda the Chained Lady | 2 passed |
| 107 | November and December are excellent months to look: after dark, the constellation is already high in the east. | EarthSky: The constellation Andromeda the Chained Lady | 2 passed |
| 108 | EarthSky adds that most people will need binoculars or a telescope to find it. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |
| 109 | Its brightness is magnitude 3.1 on NASA’s page. | NASA Science: Hubble’s Messier Catalog, Messier 31 (the Andromeda Galaxy) | 1 passed |
| 110 | EarthSky gives magnitude 3.5. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |
| 111 | Visit Isle of Man lists the Great Andromeda Galaxy among the sights you can see from the island’s dark sky sites with your eyes alone. | Visit Isle of Man: Stargazing sites | 2 passed |
| 112 | Full Moonlight counts as light pollution for the fainter sights. | Royal Museums Greenwich: Astronomy without a telescope, what can I see in the night sky? | 1 passed |
| 113 | The constellation is named after Andromeda, daughter of Queen Cassiopeia and King Cepheus in Greek myth. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |
| 114 | She is the Chained Lady: chained up as a sacrifice to the sea monster Cetus, she is saved by Perseus. | EarthSky: The constellation Andromeda the Chained Lady | 3 passed |
| 115 | All the characters in the story are now constellations in the night sky. | EarthSky: The constellation Andromeda the Chained Lady | 1 passed |