Research shows that one-third of us are not getting enough sleep today, which is why a growing number of experts recommend taking more naps. So, here's what you need to know about the science of sleep, so you can plan your perfect nap: First know this: There's an ideal nap TIME. And for most people, it's halfway between the time you wake up, and when you go to bed - so, between 1pm and 4pm. Research shows that if you try napping any earlier or later, it throws off your body's circadian rhythm - which can make it harder to fall asleep at your "normal" bed time. Another nap fact: The ideal PLACE to nap is "whatever works" - whether it's in a parked car, on a couch, or curled up under your desk. Just know that it's easier to take short naps if you're sitting upright. Which brings us to this question: HOW LONG should we nap? According to sleep expert Dr. Sara Mednick, that depends on your napping goal. For example: If you're looking for a quick energy boost, aim for a "power nap" no longer than 20-minutes. Because short naps are proven to help us feel sharper and more alert for at least 2 hours. Plus, a study in the journal Sleep says that a 20-minute nap limits us to the lightest stage of sleep, so we'll wake up, without feeling groggy. Next, if your goal is to get a memory boost - say, before a test, aim for a 60-minute nap. Dr. Mednick says that gives you time to enter the deepest "slow wave sleep" - where most of the brain's memory consolidation happens. And studies show it's the best phase for memorizing facts, faces, and names. The catch? When you wake from slow wave sleep, it can take up to an hour to shake off your grogginess. Finally, if your goal is to completely reboot your brain, go for a 90-minute nap. Our expert says this gives you time for a full cycle of sleep - including the "REM sleep" phase, when we're most likely to dream. Which provides the full restorative benefits of a nap. So when we wake up, we're ready for any challenge that comes our way - from riding a bike to playing a piano.