The first observer to catalog differences in star brightnesses was Greek astronomer Hipparchus. He created a catalog around 135 B.C.E. of roughly 850 stars divided into six ranges. He called the ...

You know that M31 (NGC 224) in Andromeda is another galaxy far outside our own Milky Way, don’t you? Of course you do! Everyone knows that. But we haven’t always known it. In fact, we’ve only known ...