As summer nears its close, many of us are flying away to get our last taste of summer vacation, but nothing ruins a good jaunt to Europe like a bout of jet lag. In fact, jet lag was once considered such a problem that Congress set up a special unit at NASA devoted to studying the condition. Joining us to explain why jet lag occurs and how we can prevent it are Dr. Kevin Gregory, a former scientist at the NASA Jet Lag Center and the current senior scientist at Alertness Solutions Inc., and Dr. David M. Rapoport, Director of the Sleep Medicine Program at NYU Medical School.