FraunhoferLinien

Fraunhoferlinien, or Fraunhofer lines, are dark absorption features observed in the solar spectrum. They were identified and cataloged by the German physicist Joseph von Fraunhofer in 1814, and the set is named after him. These lines occur where photons at specific wavelengths are absorbed by atoms and ions in the Sun’s outer layers, as well as by molecules and atoms in Earth’s atmosphere, producing a spectrum punctuated by narrow, dark features.

Fraunhofer compiled a high-resolution spectrum and assigned wavelengths to hundreds of individual lines, establishing a reference framework for wavelength calibration in spectroscopy. Among the most familiar lines are the sodium D lines near 589 nanometers and the calcium II H and K lines near 396.8 and 393.4 nanometers. The solar spectrum also contains numerous other metal lines from iron, magnesium, titanium, and more, as well as hydrogen lines from the Balmer series.

The Fraunhoferlinien have had a profound impact on physics and astronomy. They enable determination of the Sun’s chemical composition, temperature, and density in its atmosphere, and they allow astronomers to measure Doppler shifts that reveal motions within stars and galaxies. Magnetic fields can be studied via Zeeman splitting in certain lines, providing insights into solar and stellar magnetism. Today the lines continue to serve as fixed reference standards for spectrograph calibration and for comparative spectroscopy across wavelengths and instruments.

A portion of the solar spectrum contains telluric lines produced by Earth’s atmosphere, which can blend with or obscure solar features. Distinguishing solar Fraunhofer lines from telluric features remains a routine part of spectral analysis.