Keck Observatory
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.
 The Keck observatory domes atop Mauna Kea | |
| Alternative names | Keck telescope  |
|---|---|
| Part of | Mauna Kea Observatories |
| Location(s) | Hawaii |
| Coordinates | 19°49′35″N 155°28′28″W |
| Altitude | 4,145 m (13,599 ft) |
| Built | September 1985 –1996 |
| First light | 24 November 1993, 23 October 1996 |
| Telescope style | astronomical observatory optical telescope reflecting telescope |
| Number of telescopes | 2 |
| Diameter | 10 m (32 ft 10 in) |
| Angular resolution | 0.04 arcsecond, 0.4 arcsecond |
| Collecting area | 76 m2 (820 sq ft) |
| Focal length | 17.5 m (57 ft 5 in) |
| Mounting | altazimuth mount |
| Enclosure | spherical dome |
| Website | keckobservatory |
  Location of Keck Observatory | |
However, all of the light collected by the Keck Observatory primary mirrors (75.76m2) is sent to the secondary mirror and the instruments, compared to GTC's primary mirror, which has an effective light-collection area of 73.4m2, or 25.4 square feet less than each of the Keck Observatory primary mirrors. Because of this fundamental difference in design, Keck Observatory's telescopes arguably remain the largest steerable, optical/infrared telescopes on Earth.