Hale Telescope mirror.. It was completed in 1948 and is still in active use. The Hale Telescope represented the technological limit in building large optical telescopes for over 30 years. It was the largest telescope in the world until the Russian BTA-6 was built in 1976, and the second largest until the construction of the Keck Observatory Keck 1 in 1993. Hale supervised the building of the telescopes at the Mount Wilson Observatory with grants from the Carnegie Institution of Washington: the telescope in 1908 and the telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding
Telescope the task they perform such as [[astrograph]]s, [[comet seeker]]s and [[solar telescope]]s. [[File:USA.NM.VeryLargeArray.02.jpg|thumb|200px|The [[Very Large Array]] at Socorro, New Mexico, United States.]] Radio telescopes are [[Directional antenna|directional]] [[radio antennas]] used for [[radio astronomy]]. The dishes are sometimes constructed of a conductive wire mesh whose openings are smaller than the [[wavelength]] being observed. Multi-element [[Radio telescope]]s are constructed from pairs or larger groups of these dishes to synthesize large 'virtual' apertures that are similar in size to the separation between the telescopes; this process is known as [[aperture synthesis]]. As of 2005, the current record array size is many times the