When it comes to sleep, there’s a lot to learn, and scientists are still trying to figure out a lot of things. One of the things that’s become more clear over the years is the importance of napping. In the fourth of our 11 weekly infographics (which, when tallied up, will feature 80 facts about sleep) we provide information on how much you should nap, when you should nap, and information about historical figures who were vigorous nappers.