W. M. Keck Observatory Headquarters

From the summit of Hawaii’s dormant Mauna Kea volcano (14,000 ft in elevations), astronomers at the W. M. Keck Observatory probe the local and distant Universe with unprecedented power and precision. Their instruments are the twin Keck telescopes—the world’s largest optical and infrared telescopes. Each telescope stands eight stories tall, weighs 300 tons and operates with nanometer precision. The telescopes’ primary mirrors are 10 meters in diameter and are each composed of 36 hexagonal segments that work in concert as a single piece of reflective glass. In the middle of the Pacific Ocean, Hawai’i Island is surrounded by thousands of miles of thermally stable seas. The 13,796-foot Mauna Kea summit has no nearby mountain ranges to roil the upper atmosphere. Few city lights pollute Hawaiian night skies, and for most of the year, the atmosphere above Mauna Kea is clear, calm and dry. Because of the large size of the 10-meter primary mirrors, the Keck telescopes offer the greatest potential sensitivity and clarity available in astronomy. Their performance, and the performance of all ground-based telescopes, is limited by the turbulence of the Earth’s atmosphere, which distorts astronomical images. Astronomers have recently overcome the effect of atmospheric blurring using an established and fundamental technique called adaptive optics (AO). AO corrects for the image distortions by measuring and then correcting for the atmospheric turbulence using a deformable mirror that changes shape 2,000 times per second. In 1999, the Keck II telescope became the first large telescope worldwide to develop and install an AO system. The results provided a tenfold improvement in image clarity compared to what was previously possible with Keck and other large, ground-based telescopes.