While we're able to detect tiny planets orbiting stars many light years away, and land a craft on a comet, figuring out how big the galaxy we live in turns out to be pretty hard.

New evidence from the Sloane Digital Sky Survey suggests that the Milky Way could be bigger than we thought: as much as 50% bigger. This hints that in the Milky Way's past, it may have collided with another galaxy, setting off ripples, "like a pebble in a pond"