An international team of astronomers have turned up an enormous companion galaxy to our Milky Way - it was hiding in plain sight. The star cluster is only 30,000 light years from Earth, and contains thousands of stars spread over an area 5,000 times larger than the full Moon in the sky. These stars don't fall within the Milky Way's spiral arms, galactic bulge or spherical halo, so astronomers figured they must belong to some other object. It's probably the remnant from an ancient galactic merger.