The W. M. Keck Observatory is a pair of two large, ground-based telescopes located at Mauna Kea, Hawaii. Sitting four km (more than two miles) above sea level, the paired telescopes are used to examine light from distant stars in great detail. The primary mirrors of each of the two telescopes are 10 meters (33 feet) across, making them slightly smaller than the Gran Telescopio Canarias primary mirrors.