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The angstrom, named after Anders Angstrom, is a unit of measurement equal to one ten-billionth of a meter. It has been replaced by the nanometer but is still used to measure small objects and light waves. The visible light spectrum is now expressed in nanometers, but wavelengths can also be measured in angstroms. The angstrom is considered obsolete and discouraged from use.
If you thought the nanometer was small, you haven’t come across the angstrom, but that’s probably because it preceded the nanometer. Named after Swedish spectroscopist and physicist Anders Angstrom (1814-1874), the angstrom is a legacy unit of measurement that equals one ten-billionth of a metre, or 1/10,000,000,000 of 3.28 feet. In other words, it would take 245 million angstroms to equal an inch, 10 million angstroms to equal a millimeter, or 10,000 angstroms to equal a micron. And by now you’ve guessed that with a nanometer being one billionth of a meter, it takes 10 angstroms to equal one nanometer.
In 1868 Anders Angstrom was studying solar radiation and compiled a graph of electromagnetic energy that measured light waves in increments of a ten-millionth of a millimeter. It was this unit of measurement that became known as the angstrom. Although the angstrom has been replaced by the nanometer as the unit of choice, it has traditionally been used to measure very small objects such as atoms and chemical bonds in addition to light waves and the visible light spectrum.
For humans, visible light includes those wavelengths that fall between deep purple and deep red. Light purple, for example, measures in the 4000 angstrom range, while dark red is closer to 7000 angstrom. Wavelengths at 5500 angstroms (exactly between the two extremes) would be yellow light, in the middle of the visible light spectrum. Today, however, the visible light spectrum is most often expressed as being between 400 and 700 nanometers (nm).
To offer some real-world examples of angstroms, a very fine human hair of just 50 microns would be 500,000 angstroms thick. A sheet of paper is about a million angstroms thick, and a credit card is a whopping 8 million angstroms thick.
While the angstrom has served its purpose and is still used in some technical fields, as early as 1978 the International Committee on Weights and Measures called for the withdrawal of this unit of measurement asking scientists to refrain from applying the angstrom to new applications or fields where it was not already in use. The American National Standard for Metric Practice also discouraged its use, and today the angstrom is considered obsolete.
