Carl Edward Sagan (November 9, 1934 – December 20, 1996) was an American astronomer, planetary scientist, cosmologist, astrophysicist, astrobiologist, science communicator, author, and professor. His best known scientific contribution is his research on the possibility of extraterrestrial life, including experimental demonstration of the production of amino acids from basic chemicals by radiation. He assembled the first physical messages sent into space, the Pioneer plaque and the Voyager Golden Record, which were universal messages that could potentially be understood by any extraterrestrial intelligence that might find them. He argued in favor of the hypothesis, which has since been accepted, that the high surface temperatures of Venus are the result of the greenhouse effect.

Initially an assistant professor at Harvard, Sagan later moved to Cornell, where he spent most of his career. He published more than 600 scientific papers and articles and was author, co-author or editor of more than 20 books. He wrote many popular science books, such as The Dragons of Eden, Broca's Brain, Pale Blue Dot and The Demon-Haunted World. He also co-wrote and narrated the award-winning 1980 television series Cosmos: A Personal Voyage, which became the most widely watched series in the history of American public television: Cosmos has been seen by at least 500 million people in 60 countries. A book, also called Cosmos, was published to accompany the series. Sagan also wrote a science-fiction novel, published in 1985, called Contact, which became the basis for a 1997 film of the same name. His papers, comprising 595,000 items, are archived in the Library of Congress.

Stephen William Hawking (8 January 1942 – 14 March 2018) was an English theoretical physicist, cosmologist, and author who, at the time of his death, was director of research at the Centre for Theoretical Cosmology at the University of Cambridge. Between 1979 and 2009, he was the Lucasian Professor of Mathematics at the University of Cambridge, widely viewed as one of the most prestigious academic posts in the world.

Hawking's scientific works included a collaboration with Roger Penrose on gravitational singularity theorems in the framework of general relativity, and the theoretical prediction that black holes emit radiation, often called Hawking radiation. Initially, Hawking radiation was controversial. By the late 1970s and following the publication of further research, the discovery was widely accepted as a major breakthrough in theoretical physics. Hawking was the first to set out a theory of cosmology explained by a union of the general theory of relativity and quantum mechanics. He was a vigorous supporter of the many-worlds interpretation of quantum mechanics.

Arthur Charles Clarke (16 December 1917 – 19 March 2008) was an English science fiction writer, science writer, futurist, inventor, undersea explorer, and television series host. He co-wrote the screenplay for the 1968 film 2001: A Space Odyssey, widely regarded as one of the most influential films of all time. Clarke was a science fiction writer and a futurist of a distinguished ability.

Carl Sagan

Stephen Hawking

Arthur C. Clarke