Photographed by Mindy Best.When you're planning a vacation, you sometimes have to build in extra time for jet lag. Think about it: If you're flying across several time zones, you're not going to be back on track for at least a day or two. That's just the price you pay to see the world. But, a new app could solve that small problem. Entrain, created by University of Michigan grad student Olivia Walch, uses mathematical equations to predict when you should be snoozing. All you have to do is tell the app which time zone you're entering, and it does all the fancy calculations for you. It will create a schedule indicating when to stay in bright light, low light, or complete darkness. It'll even adjust the schedule to accommodate the kind of light that's available to you at the time you're traveling. The result? Your estimated jet-lag time is pretty much cut in half. So, if for every hour you shift, you experience a day of jet lag, that trip to Australia just got a lot more realistic. We could go into the specifics about how light affects your circadian clock, but we think you should just accept the fact this app is about to change the way you travel. (NPR)