Published by the American Geophysical Union as part of the Antarctic Research Series, Volume 64. Archdeacon Stuck was seeing halos formed in moonlight. Their daytime counterparts are surprisingly common, not only in the arctic but in temperate climates as well. Many halos are possible, forming arcs of colored or white light almost anywhere in the sky. Their occasional brilliance, variety, and exotic shapes have impressed skywatchers for centuries. This book introduces halos and tries to convey some of their beauty. It tells much of what is known about them: how they arise, how so many are possible, and why some are rare, while others occur every few days or so. No such insights, of course, are necessary for the enjoyment of a halo display; indeed, an elaborate display is one of Nature"s wonders. Nevertheless, understanding can add to enjoyment, especially since the makings of a great display turn out to be as remarkable as the display itself.