The Michelson stellar interferometer is one of the earliest astronomical interferometers built and used. The interferometer was proposed by Albert A. Michelson in 1890, following a suggestion by Hippolyte Fizeau.

The first such interferometer built was at the Mount Wilson observatory, making use of its 100-inch (~250 centimeters) mirror. It was used to make the first-ever measurement of a stellar diameter, by Michelson and Francis G. Pease, when the diameter of Betelgeuse was measured in December 1920. The diameter was found to be 240 million miles (~380 million kilometers), about the size of the orbit of Mars, or about 300 times larger than the Sun.

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  Scheme of the Michelson stellar interferometer.
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  A 20-foot (~6 meters) Michelson interferometer mounted on the frame of the 100-inch (~250 cm) Hooker Telescope, 1920.
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  The Hooker Telescope interferometer on display at the Mount Wilson observatory, 2023.

• History of astronomical interferometry
• Fizeau interferometer
• Michelson interferometer

• Michelson, A. A., and Pease, F. G. (1921). Astrophys. J. 53, 249–259.