About the Author

William Sheehan (Willmar, MN) is the author of the widely acclaimed The Planet Mars and Worlds in the Sky, and coauthor (with Stephen James O'Meara) of Mars: The Lure of the Red Planet and (with Richard Baum) of In Search of Planet Vulcan. He is a frequent contributor to Astronomy and formerly a contributing editor to Sky & Telescope.

John Westfall (Antioch, CA) is professor of geography at San Francisco State University, the recipient of the Peggy Haas Service Award from the Association of Lunar and Planetary Observers, and the author of the Atlas of the Lunar Terminator.