Friday, March 14, 2008

Size Does Matters

Throughout the nineteenth and well into the twentieth century, astronomers and others interested in science and the sky avidly followed news about every new telescope that was built, each one larger than the last. In 1948, the Hale telescope at Mount Palomar, California, was dedicated. Its 200-inch (5-meter) mirror was the largest in the world.
It was designed flexibly to be used as a prime-focus instrument (with the astronomer actually ensconced in a cage at the front end of the telescope), a Cassegrain-focus instrument (with the observer perched on an adjustable platform at the back of the telescope), or a coudé-focus instrument. The Hale telescope was the largest in the world until 1974, when the Soviets completed a 74-ton, 236-inch (6-meter) mirror, which was installed at the Special Astrophysical Observatory in Zelenchukskaya in the Caucasus Mountains.
In 1992, the first of two Keck telescopes, operated jointly by the California Institute of Technology and the University of California, became operational at Mauna Kea, Hawaii. A second Keck telescope was completed in 1996. Each of these instruments combines thirty-six 71-inch (1.8-meter) mirrors into the equivalent of a 393-inch (10-meter) reflector. Not only do these telescopes now have the distinction of being the largest telescopes on Earth, they are also among the highest (of those based on Earth), nestled on an extinct volcano 2.4 miles above sea level.

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