The angstrom, also known as the angstrom unit, is a measure of displacement equal to 0.0000000001 meter (10 -10 m). It is sometimes used to express wavelength s of visible light, ultraviolet (UV) light, X rays, and gamma rays.
The visible-light spectrum extends from approximately 7700 angstroms (red light) to 3900 angstroms (violet light). This corresponds to frequencies of 390 to 770 terahertz (THz), where 1 THz = 10 12 Hz. Ultraviolet radiation, X rays, and gamma rays have progressively shorter wavelengths and higher frequencies. Some gamma rays have wavelengths less than
0.0001 (10 -4 ) angstrom.
The angstrom is not often used nowadays. It has been largely superseded by the nanometer (nm), which is 10 times larger; 1 nm = 10 angstroms = 10 -9 m.
Also see Table of Physical Units .