After 400 years of speculating about the existence of planets beyond the Solar System, work over the past two decades has finally borne fruit: our planetary home is not unique. The discovery of extrasolar planets took so long because it is hard. Picture the Sun, nearly a million miles across, as an orange in New York City. To scale, the Earth is a grain of sand 15 feet away. Standing on this grain of sand, our task is to find another grain of sand, fifteen feet from its orange — in Minneapolis. And that’s for the closest star; most of the planetary systems we’ve discovered are hundreds of times farther away. In this course, Professor Helfand will review the technology employed to accomplish this feat and present the results: thousands of new planets — including more than one hundred that are just like Earth.