A pale green interloper among the stars of Cassiopeia, Comet Hartley 2 glows like an escapee from Krypton at the center of this exposure taken on the night of Sept. 28, 2010, by NASA astronomer Bill Cooke. Still too faint to be seen with the unaided eye, the comet was 18 million miles away from Earth at the time. Cooke took this image using a telescope located near Mayhill, N.M., which he controlled via the Internet from his home computer. "Before mid-October, Northern Hemisphere observers will be able to see the comet nearly all night long in the northeast," Cook...