Which dates matter? All of them, of course. But there are some we talk about more than others, and this calendar from web comic xkcd gives those dates prime real estate. Creator Randall Munroe mined English-language books from 2000 on for mentions of dates, then expanded the corresponding numbers on the calendar; the bigger the date, the more mentions it got. Poignantly, September 11 is bigger than any other date, with January 1 and July 4 close. By contrast, Leap Day (February 29) is minuscule. It also looks like the first of every month gets mentioned regularly. Happy December 1!