Carl Sagan (1934 - 1996) was an American astronomer and popularizer of science. Through his 1980 television series Cosmos, which reached 600 million people in over 60 countries, he inspired an entire generation to become more interested in astronomy and science in general. Cosmos was the most popular PBS series of all time. Carl Sagan was a supporter of the Search for Extraterrestrial Intelligence (SETI), a founder of the field of exobiology, and a champion of secular humanism, seen widely as an alternative to religion.
Carl Sagan began his career at the University of Chicago, where he earned degrees in physics, astronomy, and astrophysics, obtaining a Ph.D in 1960. Between 1962 and 1968, he went to work for the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts. He also lectured each year at Harvard University throughout this time. In 1968, he moved to Cornell University, becoming a full professor in 1971. From 1972 to 1981, Carl Sagan was Associate Director for the Center for Radio Physics and Space Research at Cornell. From the 1950s and throughout this whole period, Sagan worked as an adviser to NASA.
Carl Sagan’s first major scientific discovery was in the early 1960s, where he analyzed radio waves reflected off the planet Venus, and came to the conclusion that the planet was dry and hot. At the time, it was popularly thought that Venus’ thick clouds concealed a balmy and possibly even habitable world. In 1962, the Mariner 2 spacecraft did a fly-by of Venus, and measured its surface temperature at 500 °C (932 °F), hot enough to melt lead, and Sagan’s conclusions were validated.
Carl Sagan was the foremost popularizer of the idea that Saturn’s moon Titan and Jupiter’s moon Europa may possess surface or subsurface oceans, and might be hospitable to hardy extraterrestrial microbes. Recently, Titan was found to have several large hydrocarbon lakes on its surface, some larger than the Great Lakes. A surface ocean on Europa has been found not to exist, but missions are in the works to send a probe to investigate the possibility of a subsurface ocean with ice-penetrating radar.
The most memorable part of Sagan’s legacy is undoubtedly his television show, which touched on a range of issues: astronomy, space travel, the Enlightenment, science fiction, and many others. In 1977, Carl Sagan released The Dragons of Eden: Speculations on the Evolution of Human Intelligence, which won a Pulitzer Prize and demonstrated Sagan’s knowledge in areas outside astronomy.