aurora borealis and aurora australis, luminous display of various forms and colors seen in the night sky. The aurora borealis of the Northern Hemisphere is often called the northern lights, and the aurora australis of the Southern Hemisphere is known as the southern lights. Each is visible over an area centering around the geomagnetic pole of its own hemisphere. The aurora borealis is said to occur with greatest frequency along a line extending through N Norway, across central Hudson Bay, through Point Barrow, Alaska, and through N Siberia. It is often visible in Canada and the N United States and is seen most frequently at the time of the equinoxes; in times of extreme activity, it may be seen in parts of the S United States. Among the most magnificent of natural phenomena, auroral displays appear in shades of red, yellow, green, blue, and violet and are usually brightest in their most northern latitudes. The aurora is seen in a variety of forms, e.g., as patches of light, in the form of streamers, arcs, banks, rays, or resembling hanging draperies. The aurora occurs between 35 mi and 600 mi (56 km-970 km) above the earth. It is caused by high-speed electrons and protons from the sun, which are trapped in the Van Allen radiation belts high above the earth and then channeled toward the polar regions by the earth's magnetic field. These electrically charged particles enter the atmosphere and collide with air molecules (chiefly oxygen and nitrogen), thus exciting them to luminosity; near the 600-mile level, the light may be given off by electrons and protons combining to form hydrogen atoms. The auroras coincide with periods of greatest sunspot activity and with magnetic storms (disturbances of the ionosphere which interfere with long-distance radio communication). Much was learned about the aurora during the 1957-58 International Geophysical Year, when it was studied intensively by means of balloons, radar, rockets, and satellites. Most of the other planets in the solar system also have auroras.

aurora australis: see aurora borealis.

Königsmark, Countess Maria Aurora, 1666-1728, Swedish noblewoman; sister of Count Philipp Christoph Königsmark. She went to Dresden in search of her missing brother and there became the mistress of Augustus II of Poland and Saxony. Their son, Maurice, was the famous Marshal de Saxe. In her last years she was abbess coadjutor at Quedlinburg.

Aurora, in Roman religion and mythology: see Eos.

Aurora. 1 City (1990 pop. 222,103), Adams and Arapahoe counties, N central Colo., a growing suburb on the east side of Denver; inc. 1903. Founded during the silver boom of the 1890s, it is now a business and technical center and Colorado's third largest city. Manufactures includes furniture, aircraft fittings, electrical equipment, precision measurement instruments, magnesium products, computer software, and paper. Tourism and construction are also important. The former Fitzsimmons Army Medical Center is being converted to business and research use. 2 City (1990 pop. 99,581), Kane co., NE Ill., on the Fox River; inc. 1837. It has large railroad yards and a variety of manufactures, including paper and plastic products, rods and bearings, controls (thermostats), foods, and consumer goods. It was one of the first cities to use electricity for street lighting (1881). It is the seat of Aurora Univ. and of a notable historical museum. A riverboat casino opened in the city in 1993.

Luminous phenomenon of the upper atmosphere that occurs primarily at high latitudes. Auroras in the Northern Hemisphere are called aurora borealis, or northern lights; in the Southern Hemisphere they are called aurora australis, or southern lights. Auroras are caused by the interaction of energetic particles (electrons and protons) from outside the atmosphere with atoms of the upper atmosphere. Such interaction occurs in zones surrounding the Earth's magnetic poles. During periods of intense solar activity, auroras occasionally extend to the middle latitudes.

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Roman goddess of dawn. Her Greek counterpart was Eos. Hesiod described her as the daughter of the Titans Hyperion and Theia. She was the sister of Helios, the sun, and Selene, the moon. By the Titan Astraeus, she became the mother of the winds and of the evening star. In Greek mythology she was also represented as the lover of the hunters Cephalus and Orion.

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