The Andromeda Galaxy

Messier 31 - The Andromeda galaxy at 2.5 million light years away from us!

M31 is the most distant thing we can see with the unaided eye. From our point of view the Moon is about 0.5 degrees across the sky. Andromeda is about 6 times bigger. This spectacular neighbor is approaching our Milky Way at about 110 kilometers per second (68 miles/s). This galactic collision is predicted to occur in about 4.5 Billion years.

Fun fact, the stars from the galaxies are sufficiently far apart that it's improbable that any of them will individually collide. For example, the nearest star to our Sun is Proxima Centauri, about 4.2 light-years away!