Carl Sagan, the beloved American astronomer ... Twitter users are sharing some of Sagan's most insightful and inspiring quotes online.

I just ran across a Charlie Rose interview with Carl Sagan that ran shortly before Sagan’s death in 1996. In it he repeated a warning that he frequently gave, which I will paraphrase.

Samuel Sagan, the 5-year-old son of the late astronomer Carl Sagan views a large color photo of the planet Mars at Planetfest 97 in Pasadena, California, July 5, 1997. Reuters Famed astronomer ...