We humans have an insatiable hunger to understand the Universe. As Carl Sagan said, "Understanding is Ecstasy." But to understand the Universe, we need better and better ways to observe it. And that means one thing: big, huge, enormous telescopes.
In this series we'll look at 6 super telescopes being built:
- The Giant Magellan Telescope
- The Overwhelmingly Large Telescope
- The 30 Meter Telescope
- The European Extremely Large Telescope
- The Large Synoptic Survey Telescope
- The James Webb Space Telescope
The Giant Magellan Telescope
The Giant Magellan Telescope (GMT) is being built in Chile, at the Las Campanas Observatory, home of the GMT's predecessors the Magellan Telescopes. The Atacamas region of Chile is an excellent location for telescopes because of its superb seeing conditions. It's extremely dry and cool there, the altitude is high, and there is little light pollution.
The GMT is being built by the USA, Australia, South Korea, and Brazil. It started facility construction in 2015, and first light should be in the early 2020's. Segmented mirrors are the peak of technology when it comes to super telescopes, and the GMT is built around this technology.
The heart of the Giant Magellan Telescope is the segmented primary mirror. Image: Giant Magellan Telescope – GMTO Corporation
The GMT's primary mirror consists of 7 separate mirrors: one central mirror surrounded by 6 other mirrors. Together they form an optical surface that is 24.5 meters (80 ft.) in diameter. That means the GMT will have a total light collecting area of 368 square meters, or almost 4,000 square feet. The GMT will outperform the Hubble Space Telescope by having a resolving power 10 times greater.
There's a limit to the size of single mirrors that can be built, and the 8.4 meter mirrors in the GMT are at the limits of construction methods. That's why segmented systems are in use in the GMT, and all of the super telescopes being designed and built around the world.
One thing that defines the GMT is the asymmetric shape of its six outer mirrors. They're described as potato chips, rather than being flat. They're also aspheric, meaning the mirrors' faces have steeply curved surfaces. The mirror's have to have exactly the same curvature in order to perform together, which requires leading-edge manufacturing. In fact, the mirrors' paraboloidal shape has to be polished to an accuracy greater than 25 nanometers. That's about 1/25th the wavelength of light itself. And each of these mirrors is 20 tons of glass.
In fact, if you took one of the GMT's mirrors and spread it out from the east coast to the west coast of the USA, the height of the tallest mountain on the mirror would be only 1/2 of one inch.
The construction of the GMT's mirrors required entirely new testing methods and equipment to achieve these demanding accuracies. That task fell on the University of Arizona's Richard F. Caris Mirror Lab.
But GMT is more than just its primary mirror. It also has a secondary mirror, which also segmented. Each one of the secondary mirror's segments must work in concert with its matching segment on the primary mirror.
The engineering behind the GMT is extremely demanding, but once it's in operation, what will it help us learn about the Universe?
"I think the really exciting things will be things that we haven't yet though of." -Dr. Robert Kirshner
The GMT will help us tackle multiple mysteries in the Universe, as Dr. Robert Kirshner, of the Harvard-Smithsonian Center for Astrophysics, explains in this video.
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