The Giant Magellan Telescope (GMT) will be the world's largest telescope when it is completed in 2025. Instead of one large mirror, the GMT will have seven separate mirrors working together. This will mean its collecting area is bigger than the actual mirror surfaces. It will be made of seven  diameter mirror parts. It will have a the resolving power of a  mirror. Its collecting area will be the same as a  mirror. The telescope will have over four times the ability to gather light than existing telescopes. It will produce images up to ten times clearer than the Hubble Space Telescope. It will cost $700 million.

Planned site
The location of the telescope is the Las Campanas Observatory, which is also the site of the Magellan Telescopes, some  northeast of La Serena, Chile. This area has clear weather for most of the year. The night sky in most of the surrounding Atacama Desert region is free from atmospheric pollution. With few cities nearby this is probably one of the places least affected by light pollution. All of this makes the area one of the best spots on Earth for long-term astronomical observation.

Design details
The telescope is unique because it will use seven mirror sections, each  in diameter.  These segments will then be arranged to form a single optical surface. This is difficult as the surface of the outer six mirror segments is not radially symmetrical (that is, they are off-axis). This requires a small change in the way mirrors are usually polished. All seven mirrors will be arranged so that the reflecting surface of each of them is on a common axis. One mirror will be in the center and the other six arranged symmetrically around the center. A focal plane will be on-axis with the entire assembly.  The plan is to build seven identical off-axis mirrors. The spare mirror has been made to replace a mirror when it needs recoating, a 1–2 week (per segment) process required every 1–2 years.

The Steward Observatory, at the University of Arizona, is making the mirrors in a laboratory beneath the university's football stadium. It is using a rotating furnace to make the mirror.  The casting of the first mirror was completed on November 3, 2005. But the time-consuming shaping and polishing will be completed in the autumn of 2011.

The telescope will make use of adaptive optics.

Member organizations
The following is a list of the group which is developing the telescope.
Observatories of the Carnegie Institution of Washington (OCIW)
 University of Chicago
 Harvard University
 Smithsonian Astrophysical Observatory
 Texas A&M University
 University of Arizona
 University of Texas at Austin
 Australian National University
 Astronomy Australia Limited
 Korea Astronomy and Space Science Institute
George P. Mitchell, founder of Mitchell Energy & Development Corp., and The Cynthia and George Mitchell Foundation are giving $25 million to help pay for the telescope.

Related pages
Atacama Desert

References

Other websites 
 Giant Magellan Telescope home page
 Article from the MIT news office
 New Scientist article on the telescope 
 COSMOS article on the telescope 
 Painted outline of the mirrors at the parking lot of the Observatories of the Carnegie Institution in Pasadena

Telescopes
Chile