An apparatus devised by A. A. Michelson which, in its original form, consisted of two pairs of flat mirrors on arms mounted across the top of the 100-inch (2.5-m) Hooker Telescope at Mount Wilson so as to increase its effective aperture. Interference fringes produced when the light was combined in the telescope allowed the diameters of stars to be estimated. A modern variant uses telescopes separated by many metres as collectors, with their light brought to a central point where techniques similar to those of aperture synthesis in radio astronomy are used to detect fine detail on stars.