Ozma Ii: The Biggest Targeted Search for Interstellar Radio Signals in the Twentieth Century

Patrick Palmer and Benjamin Zuckerman conducted a targeted search for interstellar radio signals between 1972 and 1976 known as Ozma II, observing approximately 670 nearby stars with the NRAO 300-ft radio telescope. Ozma II observed more than 300 times as many stars as Drake's 1960 Ozma project, more than 60 times as many stars as the biggest previous searches by Slysh (10), Verschuur (10), and Troitskii (11), and more than nine times as many stars as a search conducted by Bridle and Feldman around the same time as Ozma II. No other targeted search appears to have exceeded Ozma II's stellar sample size during the twentieth century. The Phoenix Project is estimated to have exceeded Ozma II's 670 stars around 2002, eventually observing approximately 800 stars by 2004. This paper describes Ozma II, places it in the context of other searches, and concludes that it was a major milestone in the search for extraterrestrial intelligence and deserves to be recognized as such.