Carl Sagan told us that there are more stars in the universe than there are grains of sand on all of the Earth's beaches. At the same time, there are more H 2 O molecules in just 10 drops of water ...

This story appears in the August 2017 issue of National Geographic magazine. Carl Sagan spent his childhood immersed in Mars. The future scientist, an avid reader of Edgar Rice Burroughs’s ...

Carl Sagan with the famous message sent on Pioneer probes, 1974. By then he knew we might find life closer to home. Credit: CBS via Getty Images Millions of space nerds reacted with joy Monday to ...