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aurora borealis
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. |
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"aurora borealis." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "aurora borealis." The Columbia Encyclopedia, 6th ed.. 2008. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1E1-aurorabo.html "aurora borealis." The Columbia Encyclopedia, 6th ed.. 2008. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1E1-aurorabo.html |
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aurora
aurora An emission of light from the Earth's high atmosphere, caused principally by oxygen atoms or nitrogen molecules that are excited by electrons accelerated within the magnetosphere. The visible aurora is dominated by the green (557.7 nm wavelength) and red (630 nm) emissions of oxygen, occurring respectively at altitudes of 100 km and above about 400 km, and red (661–686 nm) nitrogen emissions at about 95 km. Violet purple (391.4 nm) nitrogen emissions are sometimes seen in the sunlit uppermost parts of aurorae at altitudes of 1000 km.
Popularly known as the northern lights (or southern lights in the southern hemisphere), the aurora takes a number of characteristic forms. These may range from a glow, low over the northern horizon (from which the aurora borealis—‘northern dawn’—takes its name), through arcs and bands, which may be homogeneous, or may show vertical rays. Isolated rays and patches of auroral light may also be seen. Most spectacular of all is the corona, a perspective effect whereby rays appear to converge on a single region of the sky almost overhead during a particularly intense storm. During strong activity, the rays and other structures move, causing a ‘curtain’ effect, and there may often be rapid changes in brightness. The aurora is seen from the southern hemisphere as the aurora australis, a mirror-image of activity present at the same time over the opposite hemisphere of the Earth. Auroral activity is present more or less continuously around the high-latitude auroral ovals. Observers at lower latitudes, such as in the British Isles, southern United States, or Australasia, see auroral activity only when the magnetosphere is disturbed by violent solar events. Mid-latitude aurorae are usually triggered by solar flares or coronal mass ejections, and are most likely around times of high sunspot activity. Aurorae also occur on Jupiter, Saturn, Uranus, and Neptune. |
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"aurora." A Dictionary of Astronomy. 1997. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "aurora." A Dictionary of Astronomy. 1997. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O80-aurora.html "aurora." A Dictionary of Astronomy. 1997. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O80-aurora.html |
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aurora
aurora, a display of lights high in the atmosphere, known as the aurora borealis in the northern hemisphere and the aurora australis in the southern hemisphere. In Scotland the former is also known as the Northern Lights. Both auroras are most frequently seen at latitudes higher than 60°. A display consists of rapidly moving patches or columns of different coloured lights. They are most dramatic during disturbances in the earth's magnetic field and the sun is on the equinoctial, when there are periods of extensive interference with radio and telephone transmissions. They are less intense when the sunspot cycle is at its peak, when the sun emits more ultraviolet light. The UV light alters the ionization of the upper atmosphere so that it absorbs the particles being emitted from the sunspots more efficiently. But once the sun's activity has peaked, the atomic particles are able to penetrate the Van Allen radiation belt, particularly within 20° of the magnetic poles. In the upper atmosphere the particles collide with the gas molecules, exciting them to emit light in the visible spectrum. Occasionally the sun emits huge pulses of particles known as solar winds, which result in particularly spectacular displays of auroras that are visible at lower latitudes than normal.
M. V. Angel |
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"aurora." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "aurora." The Oxford Companion to Ships and the Sea. 2006. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O225-aurora.html "aurora." The Oxford Companion to Ships and the Sea. 2006. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O225-aurora.html |
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aurora
aurora Illumination of the sky, sometimes in brilliant colours, as a result of high-speed solar particles entering the ionosphere (at a height of 100–130 km) and releasing electrons from air molecules by excitation. The re-establishment of molecules leads to the emission of light, especially red- and green-coloured light, e.g. in arcs or bands over large areas. The effect is called ‘aurora borealis’ or ‘northern lights’ in the northern hemisphere and ‘aurora australis’ or ‘southern lights’ in the southern hemisphere. Such atmospheric disturbances occur in relation to disturbances on the Sun in the course of the sunspot cycle.
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AILSA ALLABY and MICHAEL ALLABY. "aurora." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. AILSA ALLABY and MICHAEL ALLABY. "aurora." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O13-aurora.html AILSA ALLABY and MICHAEL ALLABY. "aurora." A Dictionary of Earth Sciences. 1999. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O13-aurora.html |
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Aurora
Aurora in Roman mythology, the goddess of the dawn, equivalent of the Greek Eos. Most of the stories about her tell of handsome men being kidnapped to live with her.
From the early 18th century, aurora has been used to designate a natural electrical phenomenon characterized by the appearance of streamers of reddish or greenish light in the sky, especially near the northern or southern magnetic pole. The effect is caused by the interaction of charged particles from the sun with atoms in the upper atmosphere. In northern and southern regions it is respectively called aurora borealis or northern lights and aurora australis or southern lights. |
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ELIZABETH KNOWLES. "Aurora." The Oxford Dictionary of Phrase and Fable. 2006. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. ELIZABETH KNOWLES. "Aurora." The Oxford Dictionary of Phrase and Fable. 2006. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O214-Aurora.html ELIZABETH KNOWLES. "Aurora." The Oxford Dictionary of Phrase and Fable. 2006. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O214-Aurora.html |
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aurora
au·ro·ra / əˈrôrə; ôˈrôrə/ • n. (pl. au·ro·ras or au·ro·rae / ôˈrôrē/ ) 1. a natural electrical phenomenon characterized by the appearance of streamers of reddish or greenish light in the sky, usually near the northern or southern magnetic pole. 2. [in sing.] poetic/lit. the dawn. DERIVATIVES: au·ro·ral adj. |
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"aurora." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "aurora." The Oxford Pocket Dictionary of Current English. 2009. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O999-aurora010.html "aurora." The Oxford Pocket Dictionary of Current English. 2009. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O999-aurora010.html |
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aurora
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T. F. HOAD. "aurora." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. T. F. HOAD. "aurora." The Concise Oxford Dictionary of English Etymology. 1996. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O27-aurora.html T. F. HOAD. "aurora." The Concise Oxford Dictionary of English Etymology. 1996. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O27-aurora.html |
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aurora
aurora Sporadic, radiant display of coloured light in the night sky, caused by charged particles from the Sun interacting with air molecules in the Earth's magnetic field. Auroras occur in polar regions and are known as aurora borealis in the n, and aurora australis in the s.
http://www.sel.noaa.gov/pmap; http://www.spaceweather.com |
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"aurora." World Encyclopedia. 2005. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "aurora." World Encyclopedia. 2005. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O142-aurora.html "aurora." World Encyclopedia. 2005. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O142-aurora.html |
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aurora borealis
aurora borealis
•Alice, chalice, challis, malice, palace, Tallis
•aurora australis
•Ellis, trellis
•necklace
•aurora borealis, Baylis, digitalis, Fidelis, rayless
•ageless • aimless • keyless
•amaryllis, cilice, Dilys, fillis, Phyllis
•ribless • lidless • rimless
•kinless, sinless, winless
•lipless • witless • annus mirabilis
•annus horribilis • syphilis
•eyeless, skyless, tieless
•polis, solace, Wallace
•joyless
•Dulles, portcullis
•accomplice
•Annapolis, Indianapolis, Minneapolis
•Persepolis
•acropolis, cosmopolis, Heliopolis, megalopolis, metropolis, necropolis
•chrysalis • surplice • amice • premise
•airmiss • Amis • in extremis • Artemis
•promise
•pomace, pumice
•Salamis
•dermis, epidermis, kermis
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"aurora borealis." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. 11 Feb. 2012 <http://www.encyclopedia.com>. "aurora borealis." Oxford Dictionary of Rhymes. 2007. Encyclopedia.com. (February 11, 2012). http://www.encyclopedia.com/doc/1O233-auroraborealis.html "aurora borealis." Oxford Dictionary of Rhymes. 2007. Retrieved February 11, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O233-auroraborealis.html |
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