Fraunhofer lines

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Solar Fraunhofer lines
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Solar Fraunhofer lines

In physics and optics, the Fraunhofer lines are a set of spectral lines named for the German physicist Joseph von Fraunhofer (1787--1826). The lines were originally observed as dark features in the optical spectrum of the Sun.

The English chemist William Hyde Wollaston was in 1802 the first person to note the appearance of a number of dark features in the solar spectrum. In 1814, Fraunhofer independently rediscovered the lines and began a systematic study and careful measurement of the wavelength of these features. In all, he mapped over 570 lines, and designated the principal features with the letters A through K, and weaker lines with other letters.

It was later discovered by Kirchoff and Bunsen that each chemical element was associated with a set of spectral lines, and deduced that the dark lines in the solar spectrum were caused by absorption by those elements in the upper layers of the sun. Some of the observed features are also caused by absorption in Oxygen molecules in the atmosphere.

The major Fraunhofer lines, and the elements they are associated with, are shown in the following table:

Designation Element Wavelength (nm) Designation Element Wavelength (nm)
yO2898.765 cFe495.761
ZO2822.696 FH β486.134
AO2759.370 dFe466.814
BO2686.719 eFe438.355
CH α656.281 G'H γ434.047
aO2627.661 GFe430.790
D1Na589.594 GCa430.774
D2Na588.997 hH δ410.175
D3He587.565 HCa+396.847
E2Fe527.039 KCa+393.368
b1Mg518.362 LFe382.044
b2Mg517.270 NFe358.121
b3Fe516.891 PTi+336.112
b4Fe516.751 TFe302.108
b4Mg516.733 tNi299.444

The Fraunhofer C-, F-, G'-, and h- lines correspond to the alpha, beta, gamma and delta lines of the Balmer series of emission lines of the hydrogen atom.

Because of their well defined wavelengths, Fraunhofer lines are often used to characterize the refractive index and dispersion properties of optical materials.

See also

nl:Fraunhoferlijnen pt:Espectro de Fraunhofer ja:フラウンホーファー線 pl:linie Fraunhofera sv:Fraunhoferska linjerna

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