fraunhofer lines

Fraun·ho·fer lines   (froun'hō'fər)    pl.n.  A set of several hundred dark lines appearing against the bright background of the continuous solar spectrum and produced by absorption of light by the cooler gases in the sun's outer atmosphere at frequencies corresponding to the atomic transition frequencies of these gases. [After Joseph von Fraunhofer (1787-1826), German physicist.]

Main Entry: Fraun·ho·fer lines
Pronunciation: 'fraun-"hOf-&r-
Function: noun plural
: the dark lines in the spectrum of sunlight
Fraunhofer, Joseph von (1787–1826), German optician and physicist. Fraunhofer was a master theoretical optician as well as an expert maker of glass lenses and precisionoptical instruments. He effected the improvement of the homogeneity of optical glass and increased the size of the blanks free of imperfections, thus making possible the construction of large-diameterlenses. He sought to determine precisely the dispersion and index of refraction for different kinds of optical glass so that the construction of lenses could be based on optical theory and calculation.In 1814 he observed the effect of the refracting medium on light and found that the solar spectrum is crossed with many fine lines. He mapped over 570 lines that he observed between the red and violetends of the spectrum. With these lines, now known as the Fraunhofer lines, as guides, he determined with unprecedented precision the optical constants of various kinds of glass.