THE CRESCENT MOON showed through a blur of white against a sharp blue sky. Icicles and ice glaze clung to the wall of rock at the Park’s edge. Near the turnstiles the subway platform was thick with people in winter coats, and the train was still 11 minutes away. Between the brightness and the cold, the 10-year-old’s transition lenses stayed tinted all the way until the train came. A contrail held one sharp edge while the other side spread out like white paint dragged with a palette knife. The Apple Store had hung heat lamps from a fancy scaffold outside the door but no one was lined up there. Within an hour the sky had been swept to pure blue again. Paint lumps stood out on a stoplight as it hung in the lowering sun. A pair of sisters in matching snow pants went zishing along the sidewalk together.