Ångstrom , Anders Jonas

(1814–1874) Swedish physicist and astronomer

Ångstrom was born the son of a chaplain in Lögdö, Sweden. He studied and taught physics and astronomy at the University of Uppsala, where he obtained his doctorate (1839) and later became professor of physics (1858), a position he held up to his death.

Ångstrom was one of the pioneers of spectroscopy. His most important work was Optiska Undersökningar (1853; Optical Investigations), in which he published measurements on atomic spectra, particularly of electric sparks. He noted spectral lines that were characteristic of both the gas and the electrodes used. Ångstrom applied Euler's theory of resonance to his measurements and deduced that a hot gas emits light at precisely the same wavelength at which it absorbs light when it is cool. In this he anticipated the experimental proof of Gustav Kirchhoff. He was also able to show the composite nature of the spectra of alloys.

Having established the principles of spectroscopy in the laboratory, Ångstrom turned his attention to the Sun's spectrum, publishing Recherches sur le spectre solaire (1868; Researches on the Solar Spectrum) in which he made the inference that hydrogen was present in the Sun. In this work he also reported the wavelengths of some 1000 Fraunhofer lines measured to six significant figures in units of 10^–8 centimeter. Since 1905 his name has been officially honored as a unit of length used by spectroscopists and microscopists; 1 Ångstrom = 10^–8 cm. His map of the Normal Solar Spectrum (1869) became a standard reference for some 20 years. Ångstrom was also the first to examine the spectrum of the aurora borealis and to measure the characteristic bright yellow–green light sometimes named for him.