Any travel agent can tell you that a sunny beach is the perfect antidote for a foul mood. But scientific investigations into the weather-mood equation don't always show direct cause and effect.
Matthew C. Keller, a postdoctoral fellow at the Virginia Institute for Psychiatric and Behavioral Genetics, decided that researchers weren't asking the right questions. His study, published in Psychological Science, has found that moods do generally rise with temperature—with or without the beach—but only in the spring. That's probably because people savor the sun after months of deprivation, Keller says.
Even during the spring thaw, only people who spend time outside in the sunshine are likely to find themselves measurably happier. The optimal daily dose: one half hour.