This is how the Great Spiral Galaxy of Andromeda would look in the sky if it were bright enough. Sadly, its light is too faint. But imagine seeing that every night. Would you get tired of it? I know I wouldn't.
Unfortunately, it's not that bright. But it's a beautiful simulation anyway, one that gives an idea — albeit a faint one — of how huge the cosmos is. Of course, it's not the only image of this kind. Here's another one featured in NASA's Astronomy Picture of the Day:
Andromeda — or M31 — is larger than our Milky Way (although not as massive, if you count the dark matter in our galaxy.) It's 2.5 million light-years from us, while the Moon is only 384,400 kilometres away. Now think that a light-year is 9.5 trillion kilometres. Even with this graphic comparison, the size of M31 — or anything at a galactic scale — is truly incomprehensible for the human mind.
As time goes by, however, humans would start seeing it clearly at night: M31 is on a direct collision course with our home galaxy. This is what Earth's sky would look like as millenia pass by and both galaxies collide and merge:
When it happens, star systems will lose their bearings, changing orbits all around. Our own solar system will "probably be tossed much farther from the galactic core than it is today." Here's the simulation from afar:
But there's nothing to fear: the stars within the Milky Way and Andromeda are so far apart between each other than the possibility of them colliding is almost nil. And you will not be around anyway, so who cares. Just enjoy the videos and imagine the show.
Note to Galactus: the sky really needs Photoshop's Shadows and Highlights filter.
The original image used for the composite was taken by Stephen Rahn.