It’s been confirmed: the Andromeda Galaxy is heading right for us (well, our galaxy). You can see a great animation of the interaction from NASA. Don’t panic though: Andromeda won’t reach the Milky Way for 4 billion years, and it’ll take another couple of billion years after that for things to settle down as the galaxies merge. NASA also created a similation of how the night sky will change over those 6 billion years:
One quibble: the horizon is unlikely to look much like that depicted in six billion years, by which time the expanding red giant Sun will have engulfed the Earth.
In the meantime, you can check out Andromeda yourself with just a pair of binoculars. One interesting point you mightn’t realise; it’s actually much larger in the sky than suggested by the first frame above. Unlike most celestial objects, it’s not a small apparent size that makes it hard to see; it’s the fact that it’s diffuse and faint. In fact, Andromeda appears much larger in the sky than does the full Moon, as this 2006 APOD montage demontrates:
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You need good light collection capabilities (long exposures), not better magnification, to see the outskirts of Andromeda like this. Ironically, the smaller Magellanic Cloud galaxies are much easier to see with the naked eye (they were easy to spot while camping in Australia as a kid), as their light is packed into a much smaller region of the sky. In fact, I think I might get out the telescope this weekend and check out some Northern sky objects. Enjoy your weekend, too.
