NEIL deGRASSE TYSON is an astrophysicist and the director of the Hayden Planetarium at the American Museum of Natural History in New York City. He is the author of many science books for a general audience, among them Space Chronicles: Facing the Ultimate Frontier (2012) and The Pluto Files: The Rise and Fall of America’s Favorite Planet (2014). He is an informative and entertaining tweeter @neiltyson and writes the “Universe” column in Natural History magazine, where this essay was published in 2007.