Astronomers have discovered a clump of 73 quasars spanning four billion light years at its widest point -- that's like 40,000 Milky Way galaxies lined end-to-end.
For 520 days, six men lived together in a simulated mission to Mars. Here's what their home away from home looked like.
The comet ISON, discovered by two amateur astronomers last year, will zoom past Earth next fall. But where did it come from?