Lucy, whose real name is BPM 37093, is a diamond roughly the size of our moon. At around 4000 kilometers in diameter (2,485 miles), Lucy is estimated to be around 10 billion trillion trillion carats. A billion trillion trillion? x 10? It's easier to imagine dividing by zero than to put this ridiculous number into perspective.
What's the story behind this huge diamond? According to BBC News,
"It's the compressed heart of an old star that was once bright like our Sun but has since faded and shrunk. Astronomers have decided to call the star "Lucy" after the Beatles song, Lucy in the Sky with Diamonds.
The diamond star completely outclasses the largest diamond on Earth, the 546-carat Golden Jubilee which was cut from a stone brought out of the Premier mine in South Africa."