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The density varies with season; the average column density (the number of atoms per unit area above any point on the Earth's surface) is roughly 4 billion sodium atoms/cm. For a typical thickness of 5 km this corresponds to volume density of roughly 8000 sodium atoms/cm.
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Atoms of sodium in this layer can become excited due to sunlight, solar wind, or other causes. Once excited, these atoms radiate very efficiently around 589 nm, which is in the yellow portion of the spectrum. These radiation bands are known as the
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and has a depth of about 5 km (3.1 mi). The sodium comes from the
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proposed a reaction-cycle theory to explain the night-glow phenomenon.
90:. Atmospheric sodium below this layer is normally chemically bound in
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The sodium layer was first discovered in 1929 by
American astronomer
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to compensate for movements in the atmosphere. As a result, optical
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have found the sodium layer to be useful for creating an artificial
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can perform much closer to their theoretical limit of resolution.
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and used to excite sodium atoms in the upper atmosphere. (
98:, while the sodium atoms above the layer tend to be
116:. The resulting radiation is one of the sources of
176:Ageorges, N.; Hubin, N.; Redfern, R.M. (1999),
188:, Garching: European Southern Observatory: 3,
178:"Atmospheric Sodium Column Density Monitoring"
78:range of 80–105 km (50–65 mi) above
45:Frequency Addition Source of Optical Radiation
130:in the upper atmosphere. The star is used by
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182:ESO Conference and Workshop Proceedings
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16:Thin layer of Earth's upper atmosphere
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74:. This layer usually lies within an
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35:experiments is tuned to the
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25:Starfire Optical Range
224:Metallic vapor layers
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244:Astronomical imaging
23:A FASOR used at the
194:1999ESOC...56....3A
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196:, archived from
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128:laser guide star
33:laser guide star
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132:adaptive optics
37:sodium D2a line
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218:External links
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157:Sydney Chapman
145:. In 1939 the
113:sodium D lines
55:is a layer of
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203:on 2012-03-19
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143:Vesto Slipher
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205:, retrieved
198:the original
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154:geophysicist
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96:sodium oxide
53:sodium layer
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124:Astronomers
43:stands for
239:Atmosphere
233:Categories
207:2011-09-04
163:References
136:telescopes
72:mesosphere
92:compounds
80:sea level
151:American
118:air glow
94:such as
84:ablation
76:altitude
190:Bibcode
147:British
100:ionized
88:meteors
66:within
57:neutral
249:Sodium
64:sodium
201:(PDF)
68:Earth
60:atoms
41:FASOR
29:LIDAR
51:The
31:and
27:for
86:of
70:'s
62:of
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47:.)
192::
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