Giant Magellan Telescope. Artwork of the Giant Magellan Telescope (GMT), an optical telescope comprising 7 primary mirrors, each with a diameter of 8.4 metres. The mirrors combine to form a light gathering aperture of 21.5 metres which is reflected to a secondary mirror located above. The secondary mirror utilises adaptive optics to compensate for distortions from the Earth's atmosphere. This type of telescope design is known as a Gregorian system and will eventually be housed in a steel enclosure. The GMT will be located in northern Chile and is scheduled to be completed in 2016.