An Ancient Universe: How Astronomers Know the Vast Scale of Cosmic Time



These two domes house the twin Keck Telescopes perched high above the clouds on Mauna Kea (an extinct volcano) on the Big Island of Hawaii. Each dome contains a telescope with many mirror segments, which combine to give a light collecting area of 10 meters (about 10 yards) across. These are currently the largest light-collecting telescopes in the world, although the European Southern Observatory is building a series of four giant telescopes in Chile which will have a larger collecting area when their light is combined. With such telescopes, astronomers can detect the light of very distant (and thus faint) objects. (Courtesy of William Keck Observatory and Caltech)

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