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Land and Climate of Antarctica

Optical Phenomena in Antarctica

Antarctica experiences many unusual atmospheric optical phenomena. Most spectacular is the aurora australis (southern lights), caused by entry into the upper atmosphere of streams of charged particles (mainly protons and electrons) from the Sun. Deflected by the Earth’s magnetic field, the particles collide with atoms and molecules of atmospheric gases 100 to 140 km (60 to 90 mi) above the Earth’s surface. This produces light in characteristic rays, bands, and rings of various hues. Within the southern auroral zone—a wide circle about 4,000 km (about 2,000 mi) in diameter and centered around the geomagnetic pole (the south end of the axis of the geomagnetic field that surrounds the Earth)—auroral displays are visible almost every winter night, including the 24-hour-long polar night.

Refraction of light from the Sun and Moon by concentrations of ice crystals in the lower atmosphere produces iridescent clouds in the sky and rainbow-like halos around the Sun and Moon. Similar atmospheric distortions produce colored disks resembling the Sun and Moon—called parhelia, or sun dogs, and parselene respectively—as well as colored arches in the sky. More rarely, high altitude ice clouds called noctilucent clouds are visible after sunset. Dry atmosphere chilled by contact with the cold surface of Earth gives rise to spectacular mirages, in which distant objects are raised above the horizon to appear misleadingly close.

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