ANN ARBOR—Moonless nights outside the Cerro Tololo astronomical observatory in Chile are so dark that when you look down, you can't see your feet. "You can't see your hands," said David Gerdes, physics professor at the University of Michigan. "But you can hold them up to the sky and see a hand-shaped hole with no stars in it. It's really incredible." From this site in the Andes over the next five years, an international team will map one-eighth of the sky in unprecedented detail—aiming to make a time lapse of the past 8 billion years of a slice of the...