Some Giant Telescopes

Radio (dish-antenna) telescopes: The fixed-dish telescope (1963) near Arecibo, Puerto Rico: 1,000 ft (305 m) in diameter, covering 25 acres.
Very Large Array (VLA) radio telescope (1980) near Socorro, N.M. It has 27 mobile dishes, each 82 ft in diameter.
The fully steerable radio telescope (1972) at Effelsberg, Germany: 328 ft (100 m) in diameter.
The fully steerable radio telescope (2000) at Green Bank, W. Va.: 328 by 360.89 ft (100 by 110 m) in diameter.
Optical (mirror) telescopes:Hale telescope (1948) at Mt. Palomar, Calif. The reflector is 200 in. (5 m) in diameter.
W. M. Keck telescope (1991) at Mauna Kea, Hawaii. Its primary mirror is composed of 36 hexagonal segments, each 5.9 ft (1.8 m) across.
The European Southern Observatory (ESO) Very Large Telescope (VLT) at Cerro Paranal, Chile. It consists of four 27-ft (8.2-m) telescopes that can work independently or in combined mode. In the combined mode, the VLT has the total light-collecting power of a 52.5-ft (16-m) single telescope.
The Yerkes Observatory 40-in. (1.01-m) refractor telescope (1897) at Williams Bay, Wis.
The National Astronomical Observatory of Japan (NAOJ) Subaru telescope (1999) at Mauna Kea, Hawaii. Its single mirror is 27 ft (8.2 m) in diameter.
The Hobby-Eberly Telescope (HET) at the McDonald Observatory in West Texas. Dedicated in 1997, HET has a 9.2-m (433-in.) mirror.
The Gemini North and Gemini South twin 26.6-ft (8.1 m) telescopes. Gemini North (2000) is located atop Mauna Kea, Hawaii, and Gemini South (2001) atop Cerro Pachón, in the Chilean Andes.
The Multiple Mirror Telescope (MMT) in Arizona. The telescope's primary mirror measures 21.3 ft (6.5 m) in diameter. It went into operation in 2000.
The Magellan I (2000) and Magellan II (2002) twin telescopes at the Las Campanas Observatory in the Chilean Andes. Both have mirrors measuring 21.3 ft (6.5 m) across.
BTA (Bolshoi Teleskop Azimutalnyi, or “Large Altazimuth Telescope”) on Mount Pastukhov, in the Caucasus Range, Russia. The 19.7-ft (6-m) reflector telescope went into operation in 1976.

See also Evolution of Telescopes