An impressive solar halo, created by ice crystals in cirrus clouds that refract the incoming sunlight, seen over a palm tree near the offices of the National Solar Observatory in Tucson, Arizona, on June 27, 2006. A halo is an optical phenomenon produced by light interacting with ice crystals suspended in the atmosphere, resulting in a wide variety of colored or white rings, arcs and spots in the sky. Many halos are near the Sun or Moon, but others occur elsewhere or even in the opposite part of the sky.