aurora

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A luminous atmospheric phenomenon appearing as streamers or bands of light sometimes visible in the night sky in northern or southern regions of the earth. It is thought to be caused by charged particles from the sun entering the earth's magnetic field and stimulating molecules in the atmosphere.
• noun The dawn.

from The Century Dictionary.

• noun In electricity, an electric glow-discharge, appearing at very high voltages and some what resembling the aurora borealis.
• noun The length of time elapsing between successive maxima or minima of auroral displays, as the diurnal, the annual, the sun-spot, and the 55-year period. The last is possibly equivalent to 5 sun-spot periods. See auroral periodicity.
• noun The rising light of the morning; the dawn of day, or morning twilight.
• noun [capitalized] In Roman mythology, the goddess of the dawn: called Eos by the Greeks.
• noun The aurora borealis or the aurora australis (the polar lights).
• noun A reddish color produced by dyeing with arnotto.

from the GNU version of the Collaborative International Dictionary of English.

• noun The rising light of the morning; the dawn of day; the redness of the sky just before the sun rises.
• noun The rise, dawn, or beginning.
• noun (Class. Myth.) The Roman personification of the dawn of day; the goddess of the morning. The poets represented her a rising out of the ocean, in a chariot, with rosy fingers dropping gentle dew.
• noun (Bot.) A species of crowfoot.
• noun The aurora borealis or aurora australis (northern or southern lights).
• noun A luminous meteoric phenomenon, visible only at night, and supposed to be of electrical origin. This species of light usually appears in streams, ascending toward the zenith from a dusky line or bank, a few degrees above the northern horizon; when reaching south beyond the zenith, it forms what is called the corona, about a spot in the heavens toward which the dipping needle points. Occasionally the aurora appears as an arch of light across the heavens from east to west. Sometimes it assumes a wavy appearance, and the streams of light are then called merry dancers. They assume a variety of colors, from a pale red or yellow to a deep red or blood color.
• noun is a corresponding phenomenon in the southern hemisphere, the streams of light ascending in the same manner from near the southern horizon.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An atmospheric phenomenon created by charged particles from the sun striking the upper atmosphere, creating coloured lights in the sky. It is usually named australis or borealis based on whether it is in the southern or northern hemispheres respectively.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the first light of day
• noun an atmospheric phenomenon consisting of bands of light caused by charged solar particles following the earth's magnetic lines of force
• noun (Roman mythology) goddess of the dawn; counterpart of Greek Eos