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.
Contents |
Definition
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).
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.
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].
See also
Categories
Units of length | Non-SI metric units