Ångström

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(Redirected from Angstrom)

1 Ångström =
International units
100×10⁻¹² m	100×10⁻¹⁵ km
100×10⁻⁹ mm	1 Å
668.459×10⁻²⁴ AU	0 LY
US customary / Imperial units
3.937×10⁻⁹ in	328.084×10⁻¹² ft
109.361×10⁻¹² yd	62.137×10⁻¹⁵ mi

An ångström (symbol Å) is a non-SI unit of length that is internationally recognized. It is sometimes used expressing the size of atoms, and lengths of chemical bonds and visible-light spectra.

1 Definition
2 History
3 Representation in computers
4 See also

[edit] Definition

1 ångström (Å) = 10^–10 metres = 0.1 nm = 100 pm

For an example of lengths in this unit, the average diameter of an atom, calculated from its empirical radius, ranges from approximately 0.5 Å for hydrogen (the smallest element) to 3.8 Å for uranium (the largest naturally occurring element on earth).

[edit] History

The ångström is named after the Swedish physicist Anders Jonas Ångström (1814–1874), one of the founders of spectroscopy. Besides astrophysics, Ångström was also a student of heat transfer, terrestrial magnetism, and the aurora borealis, which was so prominent for him in his northern skies. He created a spectrum chart of solar radiation that expresses the length of electromagnetic radiation in the electromagnetic spectrum on the order of multiples of one ten-millionth of a millimeter, or 1×10^-10 meters. This unit of length became known as the ångström, Å.

From 1927 to 1960, the ångström was a secondary unit of length for use in spectroscopy, defined separately from the meter, which was still defined based on a physical prototype. In 1960, the meter itself was redefined in spectroscopic terms, making the ångström obsolete.

[edit] Representation in computers

Unicode includes the "ångström sign" at U+212B (Å). However, the "ångström sign" is canonically decomposed into U+00C5 (Å), thereby seen as a (pre-existing) encoding mistake, and it is better to use U+00C5 (Å) directly.

When typing the ångström sign into Excel or other processing programs, it is important to type in [A]~0(2) + Ctrl-W in order for it to be formatted correctly. Word processors do not have this symbol directly included and so it must be input as mentioned.

On a Macintosh, the keyboard shortcut for Å is [Option-Shift-A].