unit of length
accuracy=5 An ångström or angstrom (symbol
Å) (pronEng|ˈɔːŋstrəm; Swedish: IPA2|ˈɔ̀ŋstrœm) is an internationally recognized non- SIunit of length equal to 0.1 nanometreor 1e|−10 metres. It is sometimes used in expressing the sizes of atoms, lengths of chemical bonds and visible-light spectra, and dimensions of parts of integrated circuits. It is commonly applied in structural biology. It is named after Anders Jonas Ångström.
The ångström is named after the Swedish
physicist Anders Jonas Ångström(1814–1874), one of the founders of spectroscopywho is known also for studies of astrophysics, heattransfer, terrestrial magnetism, and the aurora borealis.
In 1868, Ångström created a spectrum chart of
solar radiationthat expresses the wavelengthof electromagnetic radiationin the electromagnetic spectrumin multiples of one ten-millionth of a millimetre, or 1e|−10 meters. This unit of lengthbecame known as the "Ångström unit", and later simply as the "ångström".
The visual sensitivity of a human being is from about 4,000 ångströms (violet) to 7,000 ångströms (dark red) so the use of the ångström as a unit provided a fair amount of discrimination without resort to fractional units. Because of its closeness to the scale of atomic and molecular structures it also became popular in
Although intended to correspond to 1e|−10 metres, for precise spectral analysis the ångström needed to be defined more accurately than the metre which until 1960 was still defined based on the length of a bar of metal held in
Paris. In 1907 the International Astronomical Uniondefined the international ångström by making the wavelength of the red line of cadmiumin air equal to 6438.46963 international ångströms, and this definition was endorsed by the International Bureau of Weights and Measuresin 1927. From 1927 to 1960, the ångström remained a secondary unit of length for use in spectroscopy, defined separately from the metre, but in 1960, the metre itself was redefined in spectroscopic terms, thus aligning the ångström as a submultiple of the metre.
Today, the use of the ångström as a unit is less popular than it used to be and the nanometre (nm) is often used instead (with the ångström being officially discouraged by both the International Committee for Weights and Measures and the
American National Standard for Metric Practice).
Unicodeincludes the "angstrom sign" at U+212B (Å). However, the "angstrom sign" is normalized into U+00C5 (Å), and is thereby seen as a (pre-existing) encoding mistake, and it is better to use U+00C5 (Å) directly. [cite book |title=The Unicode Standard |url=http://www.unicode.org/versions/Unicode5.0.0/ |format=PDF |accessdate=2007-07-06 |edition=Version 5.0 |isbn=0-321-48091-0 |pages=493 |chapter=Symbols |chapterurl=http://www.unicode.org/versions/Unicode5.0.0/ch15.pdf |author=the Unicode Consortium. Ed. by Julie D. Allen ... |year=2006 |publisher=Addison-Wesley |location=Upper Saddle River, NJ [etc.] |oclc=145867322 ]
Conversion of units
1 E-10 m
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