The Very Large Telescope (VLT) is located at the Paranal Observatory in Chile's Atacama desert, and is the world's most advanced optical telescope. It comprises four 8.2 metre reflecting telescopes and three auxiliary 1 metre telescopes that can move about.
The VLT produces extremely sharp images using a special technique called optical inferometry (i.e. combining the light from all telescopes) and can capture light from the faintest and most remote objects in the Universe.
The Gran Telescopio Canarias, also known as GranTeCan or GTC, is a 10.4 metre telescope, which began operations in 2009. The GTC Project is a partnership between Spain, Mexico, the University of Florida and the Instituto de AstrofÃsica de Canarias (IAC).
The William Herschel Telescope (WHT) is the largest UK owned telescope in the Canary Isles, and indeed throughout the northern hemisphere. It was built during the 1980's and first saw operation in 1987.
At 11 metres in diameter, the Southern Africa Large Telescope (SALT) is the largest single optical telescope in the southern hemisphere, able to detect stars one billion times dimmer than the faintest visible to the unaided eye. It is sited at the Southern Africa Observatory site near Sutherland, Northern Cape.
The main mirror, however, is not one single piece of glass, but made up of 91 hexagonal mirror segments which are all carefully joined and aligned to reflect the light as if they were one mirror.
Commissioned way back in 1974, the Anglo-Australian Telescope was one of the last 4 metre equatorially mounted telescopes to be constructed. Such telescopes are tilted to align with the rotation of the Earth, and follow or track a star through the sky they only have to move in one direction. Most modern large telescopes have to move in two directions to follow a star - a more complicated technique but possible these days with the advent of modern computers.