An angstrom is a unit of measurement used to express very small distances, particularly in the fields of physics and chemistry. It is equal to one ten-billionth of a meter (10^-10 meters) and is often used to describe the size of atoms and the wavelengths of light. The symbol for angstrom is Å. This unit is especially useful in the study of molecules and crystals, where dimensions are on the atomic scale. For example, the diameter of a hydrogen atom is about 1 Å, while the wavelength of visible light ranges from approximately 4000 to 7000 Å.