High Quality Content by WIKIPEDIA articles! The W. M. Keck Observatory is a two-telescope astronomical observatory at an elevation of 4,145 metres (13,600 ft) near the summit of Mauna Kea in Hawai`i. The primary mirrors of each of the two telescopes are 10 metres (33 ft) in diameter, making them the second largest optical telescopes in the world, slightly behind the Gran Telescopio Canarias. The telescopes can operate together to form a single astronomical interferometer.