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"
A ring-like filament of stars wrapping around the Milky Way may actually belong to the galaxy itself, rippling above and below the relatively flat galactic plane. If so, that would expand the size of the known galaxy by 50 percent and raise intriguing questions about what caused the waves of stars.