National Geographic : 2009 Jul
TWO SETS OF NESTED DOORS TWENTY-TON CRANE Height: 80 meters (262 feet) Diameter: 100 meters (328 feet) DETAIL ABOVE ALTITUDE CRADLE STELLAR LIGHT LASERS INSTRUMENTS 1.45 meters (4.75 feet) The primary mirror has 984 segments. • BIGGEST OF THEM ALL With a mirror four times wider than today's most powerful telescopes, the 42-meter European Extremely Large Telescope could be a hundred times as sensitive, thanks to the clarity gained by its adaptive optics system. It will explore the origins of the first stars and galaxies, search for Earthlike planets, and investigate the dark matter and dark energy that dominate the universe. FIVE MIRROR DESIGN 1 The 42-meter primary mirror catches far-off light and reflects it to a smaller mirror centered above. 2 The 6-meter secondary mirror bounces light back down to a still smaller mirror nestled in the primary mirror. 3 This third mirror relays light to an "adaptive" mirror directly above. 4 The adaptive mirror adjusts its shape a thousand times a second to correct distortions caused by atmospheric turbulence. 5 Another mirror corrects blurring from wind hitting the telescope's dome and sends light to cameras and other instruments on the stationary platforms. STATIONARY PLATFORMS on either side of the rotatable telescope hold instruments. A TRACK can turn the 5,500-ton telescope system 360 degrees.