angstrom

[After Anders Jonas ÅNGSTRÖM.]

Symbol Å. A unit of length equal to 10⁻¹⁰ metre. It was formerly used to measure wavelengths and intermolecular distances but has now been replaced by the nanometre. 1 Å=0.1 nanometre. The unit is named after A. J. Ångström.

A unit of measurement equal to .1 nanometer, which is approximately 1/250 millionth of an inch. Angstroms are used to measure the wavelengths of light and the elements in a chip. One nanometer is equal to 10 angstroms, and one micron is equal to 10,000 angstroms. The size of an atom is three to 10 angstroms.

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[Etymology: A. J. Ångström; Sweden 1814-74] physics. Symbol Å. The length 10^-10 m = 0.1 nm, though expressed as 1.000 000 2~ × 10^-10 prior to the minor re-sizing of the metre in 1960.

History

Originally (in 1868 for solar radiations) and still used for expression of wavelengths in the electromagnetic spectrum. After elaborate measurement of the wavelength of the red line of cadmium at 6438.4696 × 10¹⁰ m, it was agreed internationally in 1907 that the angstrom be defined by assigning the value 6438.4696 Å to that wavelength
[Barrell H. Proc. Roy. Soc. London Ser. A Vol. 186, 164-70 (1946)] (in dry air containing 0.03% carbon dioxide, at standard atmospheric pressure and a temperature of 15°C). This was the pioneer use of light to define length, presaging the application to the metre in 1960, using krypton. By that time the 1907 definition had been shown to have made the angstrom 1.000 000 2~ × 10^-10 m relative to the extant prototype metre; the 1960 re-definition changed the length of the metre to make it precisely 10¹⁰ Å as defined in 1907.

The 1978 decision of the CIPM considering it acceptable to continue to use the angstrom with the SI still stands.

See also angström star; tenth metre.

A unit of length; used to express electromagnetic wavelengths; 1 Å = 10^-10 meter = ¹/10 nanometer. Abbr. Å.

A nonsystematic unit of length equal to 10⁻¹⁰ meter or 0.1 nanometer; symbol Å.