In August 1924 the United States declared a National Radio Silence Day and sent an Army cryptographer up in a Navy dirigible to listen for Martians. That surreal image opens a century-long journey through the search for extraterrestrial intelligence, from Tesla's misread static in 1899 to Frank Drake's Project Ozma in 1960 and the birth of modern SETI at Green Bank.

We explain why the 1.420 gigahertz water hole is a logical cosmic meeting place, how Jerry Ehman's 1977 Wow signal still has no explanation, and how Paul Horowitz's autocorrelation receivers scaled from Drake's single channel to 250 million channels with Project BETA. The episode also covers the cancellation of NASA's Microwave Observing Program, the privately funded Project Phoenix, the Allen Telescope Array's multi-beaming, optical SETI, Tabby's Star, technosignatures, and the ...