Auroras are luminous phenomena which appear in the high atmosphere in the form of arcs, bands, draperies, or curtains. These phenomena are usually white but may have other colors. The lower edges of the arcs or curtains are usually well defined while the upper edges are not. Polar auroras are caused by electrically charged particles, ejected from the Sun, which act on the rarefied (select) gases of the higher atmosphere. The particles are channeled by Earths magnetic field, so auroras are observed mainly near the magnetic poles. In the Northern Hemisphere they are known as aurora borealis; in the Southern Hemisphere they are known as aurora australis.

Airglow is similar in origin and nature to the aurora; it, too, is an upper atmospheric electrical phenomenon. The main differences between airglow aid aurora are that airglow is quasi-steady (quasi means seemingly) in ap-pearance, is much fainter than aurora, and appears in the middle and lower altitudes.

Aerographers Mate 3 & 2, NAVEDTRA 10363-E1, Naval Education and Training Pro-gram Development Center, Pensacola, Fla., 1976.

Aerographers Mate 1 & C, NAVEDTRA 10362-B, Naval Education and Training Pro-gram Development Center, Pensacola, Fla., 1974.

Federal Meteorological Handbook (FMH-1B), Surface Observations, NAVAIR 50-1D-1, Department of the Navy, Commander Naval Oceanography Command, NSTL Station Miss., 1 January 1980.

Glossary of Meteorology, American Meteoro-logical Society, Boston, Mass., 1959.

International Cloud Atlas, World Meteorological Organization, Geneva, Switzerland, 1956.

Meteorology For Army Aviators, United States Army Aviation Center, Fort Rucker, Ala., 1981.

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