On a freezing January morning, a thick frost covered the trees—tiny, sharp crystals; delicate white branches; fractals. This kind of frost is called "hoar frost," from an Old English adjective meaning "to show signs of age." Knobby, hunchbacked trees with white hair and beards. But frost also gives the impression of stopping time. Maybe that's what makes it seem magical, bringing to mind ice castles, white witches, and snow queens—places and people outside the rules of time, always beautiful but never changing.