Somewhere over Greenland, I opened up the window shade. People see the northern lights on their flights to Iceland, right? Might as well check. I was sitting parallel to the wing, the blue and yellow Icelandair logo lit against the black sky. But as I looked back toward the tail of the plane, I saw something else: a faint white smudge in the sky. I looked away and back a few times, and sure enough, the ligh...