Hear about the prediction of the Milky Way colliding with the Andromeda galaxy, which might happen in about four billion years

In 2012, NASA astronomers announced that they could predict with certainty the next major cosmic event to affect our solar system, the titanic collision of our galaxy with the neighboring Andromeda galaxy. Actual collisions between stars are rare, as so much of a galaxy is empty space. And collisions between galaxies take hundreds of millions of years to complete and are driven by the effect of gravity. Our galaxy, the Milky Way, is falling towards the Andromeda galaxy.

In about 4 billion years, these galaxies will collide. What will this be like? For one thing, the stars themselves won't collide, they're too sparsely distributed.

The galaxies will splash together, flinging some stars out in the process. Eventually, in about 6 billion years, these galaxies will merge. The combined system will settle down, perhaps resembling an elliptical galaxy. At that time, the Andromeda galaxy will appear as large in the sky as either of the Magellanic clouds do today.