1996: Carl Sagan dies.

Calling Carl Sagan a scientist is a little like calling the Beatles a rock band. Sagan was certainly a scientist (an astronomer, biologist and astrophysicist, to be precise). But he was also science's most visible public advocate, a secular humanist, a fervent believer in extraterrestrial life, a teacher, an author, a television host and a political activist.

While accurately fixing the surface temperature of Venus and positing the presence of seas on Jovian and Saturnian moons are among his practical contributions to the field of astronomy, his lasting contribution to humanity was to popularize the natural sciences for hundreds of millions of people.

Through his PBS series Cosmos: A Personal Voyage, Sagan reached an enormous worldwide audience. He also authored numerous books, including a sci-fi novel, that further helped popularize the natural sciences.

Reaction to Sagan from the scientific fraternity was mixed – not everyone appreciated his eager embrace of celebrity – but his professional credentials were sound, and many colleagues were pleased to see the sciences, thanks to his advocacy, rise in the public consciousness.

Sagan the scientist is perhaps best remembered as a proponent of the search for extraterrestrial life, but he enjoyed a distinguished, wide-ranging career. He helped midwife the birth of the U.S. space program and as it grew was involved in everything from devising mission experiments to briefing Apollo astronauts prior to their landing on the moon.

Sagan was deeply involved in more earthbound matters as well, and was often skeptical of technology's impact on civilization. He worried about our growing ability to annihilate ourselves through the proliferation of nuclear weapons, and he warned against our casual abuse of the planet. He was a vocal opponent of President Reagan's proposal to develop a space-based weapons program (the so-called "Star Wars" initiative) and an early voice against the dangers of global warming.

Sagan was 62 when he died from the complications of myelodysplasia, a blood deficiency linked to anemia and leukemia.

(Source: Various)