“Happy hour” is not when you might expect it to be, according to a new analysis of about half a billion Twitter messages from around the globe. On average, people are chipper when they wake up and become grouchy as the day wears on. This pattern holds true on weekends, too, but is delayed by about two hours—a trend confirmed in tweets from the United Arab Emirates, where the workweek is Sunday through Thursday. The data suggest that sleep schedules strongly influence mood cycles. The duo at Cornell University who carried out the research, published last September in Science, say that the rising popularity of online social media is allowing scientists to study human behavior in surprising new ways.

This article was published in print as "Happy in the Morning."