angstrom (Å), unit of length, equal to 10−10 metre, or 0.1 nanometre. It is used chiefly in measuring wavelengths of light. (Visible light stretches from 4000 to 7000 Å.) It is named for the 19th-century Swedish physicist Anders Jonas Ångström. The angstrom is also used to measure such quantities as atomic and molecular sizes (most elements have atoms with radii of about 1 to 2 Å) and the thickness of films on liquids.