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The Andromeda Galaxy
The furthest thing most people will ever see with their own eyes, and it is coming this way.
Seeing it from the UK and Ireland
This is the one deep sky object worth trying with nothing but your eyes. From properly dark countryside, on a moonless night in autumn or winter, it is a faint smudge of light rather than a star, and once you have found it you will always find it again. Binoculars make it easy from a decent garden. Set your expectations though: your eye sees the bright core only, as a grey oval with no colour and no spiral. The arms and the dust lanes in this photograph took a stack of exposures to bring out, and no amount of staring will show them to you. Look for it high overhead through autumn, and use the Sky Tonight page to check the Moon is out of the way.
Andromeda is the nearest big galaxy to our own, and it is the same sort of thing: a spiral disc of a few hundred billion stars turning slowly around a bright core. We see it tilted at a steep angle rather than face on, which is why it looks like a stretched oval with dark lanes cutting across it. Those lanes are dust in its spiral arms, blocking the light of the stars behind them.
It is 2.5 million light years away, and that number is the whole point of it. The light landing on the camera left Andromeda two and a half million years ago, before anything you would recognise as a human being existed. Almost nothing else you can see without equipment is that far off.
The two small ovals in the picture are its companions. The one up and to the right is M110, and the brighter one just below the core is M32. Both are small galaxies of their own, held by Andromeda the way the Moon is held by us.
It is also getting closer, at about 110 kilometres every second. For years the two galaxies were expected to collide in about four and a half billion years, but newer measurements from 2025 put the chance of a merger at only about even over the next ten billion. Nobody will be standing on the Earth to watch either way, but it is a rare case of a picture showing you something genuinely on its way.
The numbers
- Also called
- M31, and NGC 224
- Distance
- 2.5 million light years
- Width
- Roughly 150,000 light years, a little larger than our own galaxy
- Brightness
- Magnitude 3.4, naked eye from a dark sky
- Companions in the picture
- M110 above right, M32 below the core
- Closing speed
- About 110 kilometres per second
- Merger with the Milky Way
- About an even chance within 10 billion years
- Best months from the UK and Ireland
- September to February
To find out whether it is up tonight, and when it gets properly dark where you are, see Sky Tonight.