Although his Cosmos series is nearly 20 years old, it remains as relevant today as it did in the early 1980s. Here are some excellent video excerpts from the series.
One Thousand Years of Darkness : Sagan discusses the destruction of the Library of Alexandria and why the momentous discoveries of the ancient world were unable to prevent the dark ages from virtually banishing scientific thought for a millennium. A sobering statement on what ignorance, apathy and fanaticism can do if left unchallenged.
4th Dimension Explanation : from world famous astronomer and astrophysicist legendary Carl Sagan
Drake Equation :
Search for Extraterrestrial Intelligence :