Nanometre

The nanometre (International spelling as used by the International Bureau of Weights and Measures; SI symbol: nm) or nanometer (American spelling) is a unit of length in the metric system, equal to one billionth of a metre ( 6991100000000000000♠0.000000001 m) . The name combines the SI prefix nano- (from the Ancient Greek νάνος, nanos, "dwarf") with the parent unit name metre (from Greek μέτρον, metrοn, "unit of measurement"). It can be written in scientific notation as 6991100000000000000♠1×10⁻⁹ m, in engineering notation as 1 E−9 m, and is simply 1/1 000 000 000 m. One nanometre equals ten ångströms.

Use

The nanometre is often used to express dimensions on an atomic scale: the diameter of a helium atom, for example, is about 0.1 nm, and that of a ribosome is about 20 nm. The nanometre is also commonly used to specify the wavelength of electromagnetic radiation near the visible part of the spectrum: visible light ranges from around 400 to 700 nm. The angstrom, which is equal to 0.1 nm, was formerly used for these purposes.