Telescopes have grown in size since they first appeared around 1608. The following tables list the increase in size over the years. Different technologies can and have been used to build telescopes, which are used to magnify distant views and gather light (especially important in astronomy).
Roque de los Muchachos Observatory (Spanish: Observatorio del Roque de los Muchachos, ORM) is an astronomical observatory located in the municipality of Garafía on the island of La Palma in the Canary Islands, Spain. The observatory site is operated by the Instituto de Astrofísica de Canarias, based on nearby Tenerife. ORM is part of the European Northern Observatory.
The seeing statistics at ORM make it the second-best location for optical and infrared astronomy in the Northern Hemisphere, after Mauna Kea Observatory, Hawaii. The site also has some of the most extensive astronomical facilities in the Northern Hemisphere; its fleet of telescopes includes the 10.4 m Gran Telescopio Canarias, the world's largest single-aperture optical telescope as of July 2009, the William Herschel Telescope (second largest in Europe), and the adaptive optics corrected Swedish 1-m Solar Telescope.
William Herschel's 40-foot telescope, also known as the Great Forty-Foot telescope, was a reflecting telescope constructed between 1785 and 1789 at Observatory House in Slough, England. It used a 48-inch (120 cm) diameter primary mirror with a 40-foot-long (12 m) focal length (hence its name "Forty-Foot"). It was the largest telescope in the world for 50 years. It may have been used to discover Enceladus and Mimas, the 6th and 7th moons of Saturn. It was dismantled in 1840 by Herschel's son John Herschel due to safety concerns; today the original mirror and a 10-foot (3.0 m) section of the tube remain.