American astronomer

One of the first scientists to take an active interest in the possibility that life exists elsewhere in the Universe, and an astronomer that was both a best-selling author and a popular television figure, Carl Sagan was one of the best-known scientists in the world. Sagan made important contributions to studies of Venus and Mars, and he was extensively involved in planning NASA's Mariner missions. Regular appearances on the Tonight Show with Johnny Carson began a television career that culminated in the series Sagan hosted on public television called Cosmos, seen in sixty countries by over 400 million people. He was also one of the authors of a paper that predicted drastic global cooling after a nuclear war; the concept of "nuclear winter" affected not only the scientific community, but also national and international policy, as well as public opinion about nuclear weapons...