Angstrom

The angstrom is a <a href="/facts/Unit_of_length/C8XqXetI">unit of length</a> equal to 10−10 <a href="/facts/Metre/hPhzc1CV">m</a>; that is, one ten-<a href="/facts/Billion/d9KjEYSt">billionth</a> of a <a href="/facts/Metre/hPhzc1CV">metre</a>, a hundred-millionth of a <a href="/facts/Centimetre/urPkBdGR">centimetre</a>, 0.1 <a href="/facts/Nanometre/a98sjHyu">nanometre</a>, or 100 <a href="/facts/Picometre/Cb54mVBX">picometres</a>. The unit is named after the <a href="/facts/Swedish_people/gAeGfw2N">Swedish</a> <a href="/facts/Physicist/cQcgvSIm">physicist</a> <a href="/facts/Anders_Jonas_%C3%85ngstr%C3%B6m/y1QnJFy6">Anders Jonas Ångström</a> (1814–1874). It was originally spelled with <a href="/facts/Swedish_alphabet/9vQCp9EF">Swedish letters</a>, as Ångström and later as ångström (/ˈɒŋstrəm/). The latter spelling is still listed in some dictionaries, but is now rare in <a href="/facts/English_language/tpkxGt7b">English</a> texts. Some popular US dictionaries list only the spelling angstrom.
The unit's symbol is <a href="/facts/%C3%85/2R3BU1nc">Å</a>, which is a letter of the <a href="/facts/Swedish_alphabet/9vQCp9EF">Swedish alphabet</a>, regardless of how the unit is spelled. However, "A" or "A.U." may be used in less formal contexts or <a href="/facts/Typography/byx4sANl">typographically</a> limited media.
The angstrom is often used in the <a href="/facts/Natural_science/8hg81Q2p">natural sciences</a> and <a href="/facts/Technology/9Uav5WVR">technology</a> to express sizes of <a href="/facts/Atom/FoQ4kGN5">atoms</a>, <a href="/facts/Molecule/N9ljSfFq">molecules</a>, <a href="/facts/Microscopy/GpHlElDS">microscopic biological</a> structures, and lengths of <a href="/facts/Chemical_bond/ArNUMnIB">chemical bonds</a>, <a href="/facts/Crystallography/9B5toeqG">arrangement of atoms in crystals</a>, <a href="/facts/Wavelength/kcJU0ymz">wavelengths</a> of <a href="/facts/Electromagnetic_radiation/Ynx7ujCW">electromagnetic radiation</a>, and dimensions of <a href="/facts/Integrated_circuit/fjn6vg7C">integrated circuit</a> parts. The <a href="/facts/Covalent_radius/gLzAFRTk">atomic (covalent) radii</a> of <a href="/facts/Phosphorus/27xCeIqs">phosphorus</a>, <a href="/facts/Sulfur/IK0amTfM">sulfur</a>, and <a href="/facts/Chlorine/y27UwYBM">chlorine</a> are about 1 angstrom, while that of <a href="/facts/Hydrogen/BoYHjl0J">hydrogen</a> is about 0.5 angstroms. <a href="/facts/Visible_light/jeofpMn4">Visible light</a> has <a href="/facts/Wavelength/kcJU0ymz">wavelengths</a> in the range of 4000–7000 Å.
In the late 19th century, spectroscopists adopted 10−10 of a metre as a convenient unit to express the wavelengths of characteristic <a href="/facts/Spectral_line/HuI4Bj5f">spectral lines</a> (<a href="/facts/Monochromatic_radiation/5bzKwIH3">monochromatic</a> components of the <a href="/facts/Emission_spectrum/fxumR717">emission spectrum</a>) of <a href="/facts/Chemical_element/0jducgWD">chemical elements</a>. However, they soon realized that the definition of the metre at the time, based on a material artifact, was not accurate enough for their work. So, around 1907 they defined their own unit of length, which they called "Ångström", based on the wavelength of a specific spectral line. It was only in 1960, when the metre was redefined in the same way, that the angstrom became again equal to 10−10 metre. Yet the angstrom was never part of the <a href="/facts/SI/NShmfzlD">SI</a> system of units, and has been increasingly replaced by the nanometre (10−9 m) or picometre (10−12 m).

Angstrom open-in-new

Angstrom