Carl Sagan's Cosmos series originally aired on PBS. Titled Cosmos: A Personal Voyage, the 1980 documentary used television to explain astronomy, cosmology, evolution, and the history of scientific discovery to a mass audience.
The 13-episode series was produced by Carl Sagan Productions and KCET, a Los Angeles PBS member station. Sagan wrote and presented the program with Ann Druyan and Steven Soter, while Adrian Malone served as executive producer. Its original run lasted from September 28 through December 21, 1980.
Cosmos became a landmark for public television. It was widely reported as the most-watched series in the history of American public television until Ken Burns's The Civil War in 1990, and it later reached audiences in more than 60 countries. The companion book and soundtrack helped extend its influence beyond the broadcasts.
The BBC is an understandable mix-up because it co-produced and later screened Cosmos in the United Kingdom, editing episodes to fit 50-minute slots. That later international airing does not change the answer: the original U.S. network was PBS. The series also inspired later programs, including Cosmos: A Spacetime Odyssey and Cosmos: Possible Worlds.