An astronomical interferometer is an array of telescopes or
mirror segments acting together to probe structures with higher
resolution by means of interferometry. The benefit of the
interferometer is that the angular resolution of the instrument
is nearly that of a telescope with the same aperture as a single
large instrument encompassing all of the individual photon-
collecting sub-components. The drawback is that it does not
collect as many photons as a large instrument of that size. Thus
it is mainly useful for fine resolution of the more luminous
astronomical objects, such as close binary stars. Astronomical
interferometers are widely used for optical astronomy, infrared
astronomy, submillimetre astronomy and radio astronomy. Aperture
synthesis can be used to perform high-resolution imaging using
astronomical interferometers. Very Long Baseline Interferometry
uses a technique related to the closure phase to combine
telescopes separated by thousands of kilometers to form a radio
interferometer with the reso