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	Frequently Asked Questions Send to a friend  Printable version  En Español Keywords Telescopes and Modern Observatories  Hubble Space Telescope  Radio Astronomy  Resources FAQs about Astronomers and Observatories Astronomy Gift Shop 2009 Sky Almanac McDonald Observatory logo cap What is the largest telescope?  The Keck telescopes in Hawaii are the world's largest. The largest visible-light telescopes currently in operation are the Keck I and II telescopes on Mauna Kea in Hawaii. Each uses an array of 36 computer-controlled mirror segments to provide the light-gathering power of a single 10-meter (33-foot) mirror. The Hobby-Eberly Telescope at McDonald Observatory near Fort Davis, Texas, houses the world's largest telescope mirror. Because of the way HET is designed, astronomers use only 9.2 meters of the 11-meter (36-foot) mirror at any one time, making HET the world’s third-largest telescope. Scheduled upgrades to the telescope, however, will improve its performance to that of a 10-meter telescope, which is the equivalent of the twin Kecks. The largest single-mirror telescope is the 8.3-meter Subaru Telescope, operated by the National Astronomical Observatory of Japan atop Mauna Kea. It saw first light in 1999. Two larger ground-based mirrors are in the planning stages: the Giant Magellan Telescope and the Thirty-Meter Telescope. The first would consist of eight individual mirrors working together, while the latter would consist of a large segmented mirror. Each would have an effective aperature of roughly 30 meters (100 feet), giving them as much surface area as a small office building. Hubble Space Telescope looks at the nether regions of the universe with a 2.4-meter mirror. The James Webb Space Telescope, which NASA plans to launch as early as 2013, will have an eight-meter (25.6-foot) primary mirror. The largest refracting telescope in the world is at Yerkes Observatory in Williams Bay, Wisconsin. Instead of a mirror, it gathers light with a 40-inch glass lens. Astronomers also gather radio waves from space using dish-shaped antennas, the largest of which is the Arecibo Observatory in Puerto Rico. Featured in the movie “Contact,” Arecibo's dish is 1,000 feet in diameter. Other FAQs Select FAQ category Earth, Moon, and the Sun The Solar System Space Probes and Human Exploration Stars and Nebulae Astronomers and Observatories Galaxies and Cosmology Stargazing and Star Lore » FAQs about StarDate Online Astronomers and Observatories Links History of Astronomy International Astronomical Union SEDS Large Telescopes Page Keck Observatory NAIC Arecibo Observatory Hobby-Eberly Telescope Space Telescope Science Institute SCOPE Home Page The Astrophysical Journal American Astronomical Society
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