The winter solstice takes place on Dec. 21. This is when the Sun — the source of heat, light and vitality — is farthest away in the sky. Nights are long, days are short and there’s a chill that blows through people’s lives. For some, it’s the perfect excuse to huddle close and get intimate. It’s no coincidence that more babies are born in late summer than at any other time of the year — do the math. But for others, the winter solstice is the time when they feel slow and sluggish. It depends on whether you’re diurnal or nocturnal by nature. If you’re a night owl, you’ll do great — but if you’re an early bird, then you may have to get one of those SAD lights to balance your mood.