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 of the world’s Super Telescopes:
- 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 Atacama region of Chile is an excellent location for telescopes because of its superb seeing conditions. It’s a high-altitude desert, so it’s extremely dry and cool there, with 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 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 in other super telescopes being designed and built around the world.
These mirrors are modern feats of engineering. Each one is made of 20 tons of glass, and takes years to build. The first mirror was cast in 2005, and was still being polished 6 years later. In fact, the mirrors are so massive, that they need 6 months to cool when they come out of casting.
They aren’t just flat, simple mirrors. They’re described as potato chips, rather than being flat. They’re 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. 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!
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 plan is for the Giant Magellan Telescope to begin operation with only four of its mirrors. The GMT will also have an extra mirror built, just for contingencies.
The construction of the GMT’s mirrors required entirely new testing methods and equipment to achieve these demanding accuracies. The entire 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 is also segmented. Each one of the secondary mirror’s segments must work in concert with its matching segment on the primary mirror, and the distance from secondary mirror to primary mirror has to be measured within one part in 500 million. That requires exacting engineering for the steel structure of the body of the telescope.
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.
The scientific aims of the GMT are well laid out, and there aren’t really any surprises. The goals of the GMT are to increase our understanding of some fundamental aspects of our Universe:
- Star, planet, and disk formation
- Extrasolar planetary systems
- Stellar populations and chemical evolution
- Galaxy assembly and evolution
- Fundamental physics
- First light and reionization
The GMT will collect more light than any other telescope we have, which is why its development is so keenly followed. It will be the first ‘scope to directly image extrasolar planets, which will be enormously exciting. With the GMT, we may be able to see the color of planets, and maybe even weather systems.
We’re accustomed to seeing images of Jupiter’s storm bands, and weather phenomena on other planets in our Solar System, but to be able to see something like that on extra-solar planets will be astounding. That’s something that even the casual space-interested person will immediately be fascinated by. It’s like science fiction come to life.
Of course, we’re still a ways away from any of that happening. With first light not anticipated until the early 2020’s, we’ll have to be very patient.