Discovery Channel Telescope, Research telescope at Happy Jack, United States.

The Discovery Channel Telescope is a Ritchey-Chrétien research telescope situated in a forested highland area of Arizona, operated by Lowell Observatory. Its primary mirror measures 4.3 meters across, making it one of the largest optical telescopes in the continental United States.

Lowell Observatory and Discovery Communications formed a partnership in February 2003 to build the telescope. A US Forest Service special-use permit for the Happy Jack site came in November 2004, and the 26-meter-tall enclosure was begun in September 2005. The 3,000 kg mirror, polished at the University of Arizona, was mounted in August 2011; construction finished in February 2012 and first light followed in April 2012.

The name comes from Discovery Communications, which formed a partnership with Lowell Observatory in February 2003 to build the telescope; the project cost $53 million. Research partners later grew to include Boston University, the University of Maryland, the University of Toledo, Northern Arizona University and Yale University. The instrument was renamed the Lowell Discovery Telescope after the broadcaster's involvement ended.

The telescope stands in the Coconino National Forest near Happy Jack, about 65 km south-southeast of Flagstaff, at 2,360 m elevation. It is a working research facility, not a public attraction, so access is arranged through Lowell Observatory rather than by turning up. The site is reached by road; the Forest Service granted a special-use permit in 2004 and an existing road was improved for construction.

The primary mirror is only about 10 centimeters (4 inches) thick despite spanning more than 14 feet (4.3 meters), making it unusually thin for its size. To stop the glass from distorting under its own weight, a system of 156 moving supports constantly adjusts the mirror's shape during observations.