9. Keck Observatory
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The dome shutters of Keck I and II top the summit of the dormant volcano Mauna Kea in Hawaii.
At an altitude of 14,000 ft (4,267.2 meters), at the top of Hawaii's Mauna Kea peak, two massive telescopes scan the universe for answers to some big questions -- how old is the universe, and how quickly is it expanding? Each 300-ton, 8-story tall telescope has an actual aperture of 10 meters (33 ft) and can collect both visible and infrared light.
The massive mirrors that collect and focus light are, like SALT's mirror, an array of smaller mirrors arranged on a perfectly formed curve. The telescopes have inner cooling systems to protect against the flexing that can come with heat exposure. But one of the greatest parts of the system is a tiny mirror that's actually supposed to flex. Even on Mauna Kea, Keck has to deal with the distortion caused by Earth's gaseous atmosphere, which is the greatest enemy to ground-based telescopes. A 6-inch (15-cm) mirror in each telescope deforms its shape 670 times per second to make up for the effects of Earth's atmosphere on incoming light [source: SALT].
The result is a pair of telescopes that can see the past. Keck can pick up light that has been traveling for billions of years. By the time this faint light hits Keck's mirrors, the event that caused it is long gone. Keck is helping astronomers determine the age of the universe and its expansion rate as well as allowing them to watch the birth of stars in other galaxies.
If Keck can see back in time, imagine what the biggest telescope in the world, the Great Canary Telescope, can pick up with its chart-topping aperture.
