Fraunhoferlijnen

Fraunhoferlinien, or Fraunhofer lines, are dark absorption lines seen in the spectrum of the Sun and other stars. They were first systematically mapped by Joseph von Fraunhofer in 1814–1815 using a prism spectroscope, revealing hundreds of narrow black lines superimposed on the continuous spectrum.

These lines arise when photons emitted inside the hot solar photosphere pass outward through cooler gas in the overlying layers, where atoms and ions absorb light at characteristic wavelengths. Additional absorption by Earth's atmosphere also imprints telluric lines. In the 1850s, Gustav Kirchhoff and Robert Bunsen showed that these lines serve as fingerprints for chemical elements, enabling identification of the constituents of stars and the Sun.

Fraunhoferlinien are fundamental in spectroscopy. They allow determination of chemical composition, physical conditions, and motions of astronomical objects. Shifts in line positions reveal radial velocities (Doppler effect). The relative strengths of lines inform about temperature and abundance. They also provided a foundation for modern spectroscopy and astrophysics, and their study led to lab-measured atomic spectra and quantum theories.

Naming: many lines are traditionally labeled with letters, such as the D line (a prominent sodium doublet), and the Ca II H and K lines near the blue end of the spectrum. While many line identifications were later linked to specific elements, some lines originate in the Earth's atmosphere (telluric lines) and must be distinguished from solar features.