Fraunhofer lines

The Fraunhofer lines or Fraunhofer lines are absorption lines in the spectrum of the sun. They are caused by resonance absorption of the gases in the solar photosphere. The Fraunhofer lines allow conclusions on the chemical composition and temperature of the gas atmosphere of the sun and stars.

Discovery

The English chemist William Hyde Wollaston in 1802 was the first observer of the dark lines in the solar spectrum. However, they were rediscovered in 1814 independently of him from Munich optician Joseph von Fraunhofer, which they then systematically studied and determined by careful measurements whose wavelengths. In total he recorded over 570 lines, among them he knew the striking with the letters A to K. The less pronounced lines received other letters.

Later Gustav Robert Kirchhoff and Robert Bunsen discovered that each chemical element was associated with a specific number and arrangement of spectral lines. They concluded from this that the observed by Wollaston and Fraunhofer lines were due to the absorption properties of these elements in the upper layers of the sun and this therefore had to be present in the photosphere. Some of the lines, however, are caused by the components of the earth's atmosphere.

Application

Due to their well-defined wavelengths, the Fraunhofer lines are often used to determine the refractive index and the dispersion of the optical materials.

In spectroscopic determination of temperature can be determined from the intensity distribution of the spectrum and with the aid of the Boltzmann distribution, the surface temperature. For example, if the Balmer lines observed in the spectrum of the sun as Fraunhofer lines, so the temperature must be so high that in some of the hydrogen atoms of the first excited state ( n = 2) is busy. For example, every 108th hydrogen atom in the first excited state at the sun with 6000 K surface temperature.

The first indications of the chemical element helium were 1868 his absorption lines in the spectrum of sunlight. In astronomy, the Fraunhofer lines are used to determine the composition of stars.

Others

The Fraunhofer C, F, G ', and h- lines are consistent with the alpha-, beta-, gamma- and delta- lines of the Balmer series of the hydrogen atom.

The lines A, B, A, Y, and Z are not solar, but terrestrial origin, that is to say: They are caused by absorption in the atmosphere.