Fraunhofer, Joseph von (1787–1826)

German physicist who did important work in optics. The dark lines in the solar spectrum (Fraunhofer lines), which reveal the chemical composition of the Sun's atmosphere, were accurately mapped by him.

Fraunhofer determined the dispersion powers and refractive indices of different kinds of optical glass. In the process, he developed the spectroscope, and in 1821 he became the first to use a diffraction grating to produce a spectrum from white light.

Fraunhofer was born in Bavaria and started work in his father's glazing workshop at the age of ten. In 1806 he entered the optical shop of the Munich Philosophical Instrument Company, which produced scientific instruments, and by 1811 he had become a director. From 1823 he was director of the Physics Museum of the Bavarian Academy of Sciences.

In 1814, to obtain more accurate optical values, he commenced using two bright yellow lines in flame spectra as a source of monochromatic light. Comparing this with sunlight, he observed that the solar spectrum is crossed with many fine, dark lines: 574 between the red and violet ends of the spectrum.

Fraunhofer constructed both diffraction and reflection gratings. By using the wave theory of light, he was able to derive a general form of the grating equation that is still in use today.