Why is sun so great?

Because I began this whole blogging thing in the dead of a nasty winter, it's only fair to mention that summer has come to Massachusetts and it is wonderful wonderful wonderful. Why why why does it make such a huge difference? Living in this climate, I veer from a borderline suicide case, holed up in the apartment in front of the TV or internet wrapped in a sleeping bag, to a thing of pure joy, flitting from BBQ to football game to beach, within a week. One moment life is a long dull struggle, the next its exploding with fabulous possibilities. You would think we could somehow train ourselves to cope with the extremes (since they should not be a surprise)--shouldn't the joy of summer (or end of winter) wear off with the years? And shouldn't we come up with strategies to fight the nastiness of winter? But no, clearly the weather is more fundamental than the things I can control with my mind. Or maybe there's no magic. It just just literally be that it has an incredibly big effect on what I do with my time and the things I do in the summer are far more pleasant.