Ångströms

Ångströms, singular ångström, symbol Å, is a non-SI unit of length equal to 10^-10 metres. In Swedish usage the plural form is ångströms; in English the plural is angstroms. The unit is widely used to express lengths on atomic and molecular scales, such as interatomic spacings, lattice constants in crystals, and wavelengths of light in the visible and near-infrared range.

The angström is named after Anders Jonas Ångström (1814–1874), a Swedish physicist and a pioneer of spectroscopy. His work on the measurement of wavelengths of light emitted by various sources helped establish the spectral scale used in early spectroscopy and solar astronomy. The unit was proposed in recognition of his contributions to the field.

For practical conversions, 1 ångström equals 10^-10 metres. Consequently, 1 nanometre (nm) equals 10 ångströms, and 1 ångström equals 100 picometres (pm). Wavelengths of visible light fall roughly in the range of about 4000–7000 Å. The angström is still encountered in older literature and in some applied sciences, particularly crystallography and spectroscopy, but in many modern contexts researchers prefer SI-derived units such as nanometres or picometres to align with standard SI practice.

Status and usage notes: the angström is not an SI base unit, but it is accepted for use with SI units as a non-SI unit. Its continued use varies by discipline and region; many journals and educators now emphasize explicit metres or nanometres to avoid ambiguity.