On 22 July 1995 two men independently discovered a previously unknown comet at about the same time. Alan Hale, a professional astronomer, saw the comet from his home in southern New Mexico, while Tom Bopp, an amateur stargazer, saw it from the Arizona desert. Named after the two men, it was known as Comet Hale-Bopp. Scientists, soon determined that the comet—a chunk of streaming ice, chemicals, and dust on a multi-millennial trip around the sun—was going to provide a great show for people on Earth. Estimated to have a nucleus twenty-five miles in diameter and a tail several million miles long, Hale Bopp was thought to be the biggest and brightest comet to come near the Earth since 1811. Though it came no closer to Earth than 122 million miles, it was easily visible to the naked eye throughout much of 1997. It was not expected to return...