Mark III Stellar Interferometer

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The Mark III Stellar Interferometer was a ground‑based optical instrument at Mount Wilson Observatory in California. It used a 32‑meter baseline to combine light from multiple telescopes, giving sharper views in visible light (about 450–800 nm). It was a collaboration between the U.S. Naval Observatory, Naval Research Laboratory, Smithsonian Astrophysical Observatory, and MIT. It operated from 1987 to 1992. After it closed, the Naval Observatory built a larger interferometer called the Navy Prototype Optical Interferometer. Mark III helped measure the details of several binary star systems, including Alpha Andromedae and Phi Cygni, among others.