Even If We're Just Dancing In The Dark

From Wiki on the Winter Solstice:

Even in modern cultures these gatherings are still valued for emotional comfort, having something to look forward to at the darkest time of the year. This is especially the case for populations in the near polar regions of the hemisphere. The depressive psychological effects of winter on individuals and societies for that matter, are for the most part tied to coldness, tiredness, malaise, and inactivity. Winter weather, plus being indoors causes negative ion deficiency which decreases serotonin levels resulting in depression and tiredness. Also, getting insufficient light in the short winter days increases the secretion of melatonin in the body, off balancing the circadian rhythm with longer sleep. Studies have proven that exercise, light therapy, increased negative ion exposure (which can be attained from plants and well ventilated flames burning wood or beeswax) can reinvigorate the body from its seasonal lull and relieve winter blues by shortening the melatonin secretions, increasing serotonin and temporarily creating a more even sleeping pattern. Midwinter festivals and celebrations occurring on the longest night of the year, often calling for evergreens, bright illumination, large ongoing fires, feasting, communion with close ones, and evening physical exertion by dancing and singing are examples of cultural winter therapies that have evolved as traditions since the beginnings of civilization. Such traditions can stir the wit, stave off malaise, reset the internal clock and rekindle the human spirit.

And, it's fun.