A metric unit of length, equal to 0.1 nanometer or 10-10?meter. Angstroms are used most often to measure the wave length of light waves. There is a technique called spectroscopy for identifying chemical substances by the wave lengths of light which they absorb (or emit, depending on the circumstances). Light shining through or from the substance is passed through a prism, which separates the various wave lengths to form a colorful spectrum. The spectrum often includes bright bands corresponding to wave lengths at which the substance emits light, or dark bands if the substance is absorbing light. The pattern of bands identifies the substance in somewhat the same way a fingerprint identifies a person. One of the pioneers of spectroscopy was the Swedish physicist Anders Jon ?ngstr?m (1814-1874), and in his honor the wave lengths of light waves are customarily stated in angstroms. Although English speakers usually pronounce the word as if it were English, the Swedish pronunciation is closer to "ong-strerm."