Aurora极光简介

1、Huifeng GengDefinition and CauseImagesColorsMythologyContentsAnauroraisanaturallightdisplayinthesky(fromtheLatinwordaurora,“sunrise”ortheRoman goddess of dawn), predominantly seen in the high latitude (ArcticandAntarctic) regions. Definition and CauseDefinition Aurorae are caused by cosmic rays（宇宙辐射

2、线）, solar wind and magnetospheric plasma（磁能层的等离子体） interacting with the upper atmosphere (thermosphere（热大气层）/exosphere（外大气层）). Their charged particles（带电粒子）, mainly electrons（电子） and protons（质子）, enter the atmosphere from above causing ionization（电离） and excitation of atmospheric constituents, and c

3、onsequent light emissions（发光）. Incident protons can also produce emissions as hydrogen atoms after gaining an electron from the atmosphere.Definition and CauseCauseImages The altitudes where aurora emissions occur were revealed by Carl Strmer and his colleagues who used cameras to triangulate more t

4、han 12,000 aurorae. They discovered that most of the light is produced between 90 and 150 km above the ground, while extending at times to more than 1000 km. Images of auroras are significantly more common today than in the past due to the increase in use of digital cameras that have high enough sen

5、sitivities. Film and digital exposure to auroral displays is fraught with difficulties, particularly if faithfulness of reproduction is an objective. Due to the different color spectrum present, and the temporal changes occurring during the exposure, the results are somewhat unpredictable. Different

6、 layers of the film emulsion respond differently to lower light levels, and choice of film can be very important. Longer exposures superimpose rapidly changing features, and often blanket the dynamic attribute of a display. Higher sensitivity creates issues with graininess.ColorRedGreenYellow and Pi

7、nkBlueAt the highest altitudes, excited atomic oxygen emits at 630.0 nm (red); low concentration of atoms and lower sensitivity of eyes at this wavelength make this color visible only under more intense solar activity. The low amount of oxygen atoms and their gradually diminishing concentration is r

8、esponsible for the faint appearance of the top parts of the curtains. Scarlet, crimson, and carmine are the most often-seen hues of red for the aurorae.At lower altitudes the more frequent collisions suppress the 630.0 nm(red) mode: rather the 557.7 nm emission (green) dominates. Fairly high concent

9、ration of atomic oxygen and higher eye sensitivity in green make green auroras the most common. The excited molecular nitrogen (atomic nitrogen being rare due to high stability of the N2 molecule) plays its role here as well, as it can transfer energy by collision to an oxygen atom, which then radia

10、tes it away at the green wavelength. (Red and green can also mix together to produce pink or yellow hues.) The rapid decrease of concentration of atomic oxygen below about 100 km is responsible for the abrupt-looking end of the lower edges of the curtains.Yellowandpinkarea mixof red and green or blu

11、e. Other shades of red as well as orange may be seen on rare occasions; yellow-green is moderately common. As red, green, and blue are the primary colors of additive synthesis（合成） of colors, in theory practically any color might be possible.At yet lower altitudes, atomic oxygen is uncommon, and ioni

12、zed molecular nitrogen takes over in producing visible light emission; it radiates at a large number of wavelengths in both red and blue parts of the spectrum, with 428 nm (blue) being dominant. Blue and purple emissions, typically at the lower edges of the curtains, show up at the highest levels of

13、 solar activity.TheValkyrior（瓦尔基里）are warlike virgins, mounted（骑上） upon horses and armed with helmets and spears.When they ride forth on their errand（使命）, their armour sheds a strange flickering light, which flashes up over the northern skies, making what Men call the aurora borealis, or Northern Lights.The ValkyriorFamous Auroras tend to be from Spanish speaking countries. Actresses include Aurora Clavel and Aurora Bautista