Aurora: Difference between revisions

Latest revision as of 18:26, 14 August 2018

aurora[edit | edit source]

A faint visual phenomenon associated with geomagnetic activity that is visible mainly in the high-latitude night sky. Aurora often occur within a band of latitudes known as the auroral oval, the location of which is dependent on geomagnetic activity. Aurora are a result of collisions between atmospheric gases and precipitating charged particles (mostly electrons) guided by the geomagnetic field from the magnetotail. Each gas (oxygen, nitrogen molecules and atoms) emits a particular color depending on the energy of the precipitating particles and the atmospheric composition, which varies with altitude. Typical aurora are 100–250 km above ground level. The colors of the aurora are normally both red and green. The red color occurs at heights around 250 km and is due to a specific transition of atomic oxygen; deeper penetrating particles (to around 100 km) interact with molecular nitrogen and oxygen causing green bands. Aurorae in the Northern Hemisphere are called aurora borealis ("northern lights") and in the Southern Hemisphere, aurorae are known as aurora australis. Patterns and forms of aurora include quiescent arcs, moving rays, patches, and veils.

Space Weather Prediction Center, 2018: Aurora. Accessed 13 August 2018. Available at https://www.swpc.noaa.gov/phenomena/aurora.

Term edited 13 August 2018.

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 == aurora ==
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-<div class="definition"><div class="short_definition">The sporadic [[radiant]] emission from the [[upper atmosphere]] over the middle and high  latitudes.</div><br/> <div class="paragraph">It is believed to be due primarily to the emission of the [[nitrogen]] molecule N<sub>2</sub>, its molecular  [[ion]] N<sub>2</sub><sup>+</sup>, and atomic [[oxygen]] [O]. According to various theories, auroras seem definitely to be  related to [[magnetic storms]] and the influx of charged [[particles]] from the sun. The exact details  of the nature of the mechanisms involved are still being investigated. The aurora is most intense  at times of magnetic storms (when it is also observed farthest equatorward) and shows a [[periodicity]]  related to the sun's 27-day rotation [[period]] and the 11-year [[sunspot cycle]]. The distribution with  height shows a pronounced maximum near 100 km. The lower limit is probably near 80 km. The  aurora can often be clearly seen, and it assumes a variety of shapes and colors that are characteristic  patterns of auroral emission. The names given to the various forms are 1) [[arcs]], which are bands  of [[light]] extending across the sky, the highest point of the arc being in the direction of the magnetic  [[meridian]]; 2) [[rays]], which may appear as single lines like a searchlight beam, or in bundles; 3)  [[draperies]], which have a curtainlike appearance, sharp on the bottom and tenuous in the upper  parts; 4) crown or [[corona]], which are seen when the rays appear to spread out from a single point  in the sky; 5) [[bands]], which are similar to the arcs, and may or may not have a ray structure; and  6) diffuse [[luminous]] surfaces, which appear as luminous clouds of indefinite shape. Sometimes the  term "streamers" is used to describe the auroral forms that extend to great heights. In northern  latitudes these displays are called [[aurora borealis]], [[aurora polaris]], or [[northern lights]]; in southern  latitudes they are called [[aurora australis]]. <br/>''Compare'' [[airglow]].</div><br/> </div>
+<div class="definition"><div class="short_definition">A faint visual phenomenon associated with geomagnetic activity that is visible mainly in the high-latitude night sky. Aurora often occur within a band of latitudes known as the [[auroral oval]], the location of which is dependent on geomagnetic activity. Aurora are a result of collisions between atmospheric gases and precipitating charged particles (mostly [[electrons]]) guided by the geomagnetic field from the magnetotail. Each gas ([[oxygen]], [[nitrogen]] molecules and atoms) emits a particular color depending on the energy of the precipitating particles and the atmospheric composition, which varies with altitude. Typical aurora are 100&#8211;250 km above ground level. The colors of the aurora are normally both red and green. The red color occurs at heights around 250 km and is due to a specific transition of atomic oxygen; deeper penetrating particles (to around 100 km) interact with molecular nitrogen and oxygen causing green bands. Aurorae in the Northern Hemisphere are called [[aurora borealis]] ("northern lights") and in the Southern Hemisphere, aurorae are known as [[aurora australis]]. Patterns and forms of aurora include quiescent arcs, moving rays, patches, and veils.</div><br/></div>
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+<p>Space Weather Prediction Center, 2018: Aurora. Accessed 13 August 2018. Available at <nowiki>https://www.swpc.noaa.gov/phenomena/aurora</nowiki>.</p><br/>
+<p>''Term edited 13 August 2018.''</p>
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