Fraunhofer lines

The dark absorption lines in the spectrum of the Sun and, by extension, in the spectrum of any star. Many of the stronger ones were first mapped by Joseph von Fraunhofer (1787-1826), who also labelled some of the most prominent with letters of the alphabet. Some of these identifying letters are still commonly used in physics and astronomy, notably the sodium D lines and the calcium H and K lines. Fraunhofer's original (1817) designations of absorption lines in the solar spectrum Letter Wavelength (nm) Chemical origin A 759.37 Atmospheric O2 B 686.72 Atmospheric O2 C 656.28 Hydrogen a D1 589.59 Neutral sodium D2 589.00 Neutral sodium D3 587.56 Neutral helium E 526.96 Neutral iron F 486.13 Hydrogen b G 431.42 CH molecule H 396.85 Ionized calcium K 393.37 Ionized calcium Note: Fraunhofer's original observations did not resolve the components of his D line.