Anders Jonas Ångström, (born August 13, 1814, Lögdö, Sweden—died June 21, 1874, Uppsala), Swedish physicist, a founder of spectroscopy for whom the angstrom, a unit of length equal to 10−10 metre, was named.
Ångström’s most important work concerned heat conduction and spectroscopy. He devised a method of measuring thermal conductivity, showing it to be proportional to electrical conductivity. In 1853 he pointed out that an electric spark yields two superposed spectra, one from the metal of the electrode and the other from the gas through which it passes. From Euler’s resonance theory Ångström deduced a principle of spectrum analysis: that an incandescent gas emits light of the same wavelength as the light it can absorb.
Ångström’s studies of the solar spectrum led to his discovery, announced in 1862, that hydrogen is present in the Sun’s atmosphere. He was the first, in 1867, to examine the spectrum of the aurora borealis and to detect and measure the characteristic bright line of oxygen in its yellow-green region at 5577 angstroms, but he was mistaken in supposing that this same line is also to be seen in the zodiacal light. In 1868 he published his great map of the solar spectrum in Recherches sur le spectre solaire (“Researches on the solar spectrum”), in which wavelength values were given in units of 10−10 metre, a unit that came to be called the angstrom. He and his collaborator Robert Thalén measured the spectral lines of many chemical elements, both in the solar spectrum and in the laboratory. Ångström and Thalén’s work soon became authoritative. However, Ångström suspected that their work contained a systematic error, and it was not until 1884, 10 years after Ångström’s death, that Thalén published results that corrected the wavelengths of some lines by as much as an angstrom. (The culprit was that Ångström and Thalén had used a value for the length of their metre standard that was too small.)
Ångström’s son Knut Johan Ångström was also a physicist who worked in spectroscopy and taught at Uppsala University.