Fraunhofer lines

Fraunhofer lines

Partial solar spectrum, showing many dark absorption lines such as Fraunhofer discovered. Some are identified with the responsible element.

Fraunhofer lines are absorption lines (dark lines) in the spectrum of the Sun, or of another star, first studied and named by Joseph von Fraunhofer in 1814. Altogether, Fraunhofer found some 700 lines in the solar spectrum. The nine most prominent he labeled with capital letters A to K, starting at the red end. The A and B bands are now known to be caused by absorption in Earth's atmosphere, while the rest are due to absorption in the Sun's photosphere. C and F are now better known as H-alpha and H-beta; the D lines are of sodium, the H and K lines of calcium, and the G band by neutral iron and the CH molecule. All these features occur generally in stars of spectral types F, G, and K.


A selection of Fraunhofer lines
lines due to wavelengths (Å)
A band O2 (molecular oxygen in Earth's atmosphere) 7594–7621
B band O2 (molecular oxygen in Earth's atmosphere) 6867–6884
C (H-alpha) H (hydrogen) 6563
a band O2 (molecular oxygen in Earth's atmosphere) 6276–6287
D1 & D2 Na (sodium) 5896 & 5890
E Fe (iron) 5270
b1, b2, b3, b4 Mg (magnesium) 5184, 5173, 5169, 5167
c Fe (iron) 4958
F (H-beta) H (hydrogen) 4861
d Fe (iron) 4668
e Fe (iron) 4384
f H (hydrogen) 4340
G Fe 4308
g Ca 4227
h (H-delta) H (hydrogen) 4102
H & K Ca (calcium) 3968 & 3934