Sodium layer

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The night glow of the sodium layer, from the perspective of the International Space Station in cross section

With sodium layer , engl. Sodium layer is an area of ​​the mesosphere in which there are unbound , non- ionized sodium atoms . The sodium layer is typically located at a height of 80 to 105 km and has a vertical extent of about 5 km; below that, sodium is mostly chemically bound, most often as sodium oxide , above it is ionized.

The sodium atoms are predominantly in the excited state and have a slightly yellowish radiation at a wavelength of 589 nm, the Fraunhofer sodium D line . This radiation is also known as night glow . The sodium comes from the abrasion of meteors .

The sodium layer was discovered by Vesto Melvin Slipher in 1929 , and in 1939 Sydney Chapman proposed a reaction cycle to explain the night glow.

In astronomy , the sodium layer is used to create artificial guide stars by means of lasers , which can be used to compensate for the deterioration in the image quality of telescopes caused by atmospheric turbulence ( seeing ).

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