Rising above 10,000 feet near the summit of Mount Graham, the Mount Graham International Observatory (MGIO) is one of the most scientifically significant astronomical sites in the world. It is operated by Steward Observatory at the University of Arizona, with construction on the site beginning in 1989. The extreme elevation, dark skies, and unusually stable atmosphere above the Pinaleño Mountains make it an exceptional location for high-precision astronomy.
Three Telescopes, One Mountain
MGIO hosts three major research telescopes. The Vatican Advanced Technology Telescope (VATT) achieved first light in 1993 and is famous as the first large telescope mirror ever cast using the University of Arizona's spin-cast mirror technique. The Submillimeter Telescope, operated by the University of Arizona Radio Observatory and originally known as the Heinrich Hertz Submillimeter Telescope, also began operating in 1993 and studies the universe at wavelengths between infrared and radio. The Large Binocular Telescope (LBT) is the site's flagship instrument, pairing twin 8.4-meter mirrors to make it one of the largest optical telescopes on Earth; it began operating with its individual mirrors in 2004 and moved to full joint binocular operation in 2008.
History and Significance
The observatory's high-altitude site was chosen for its combination of elevation, low light pollution, and atmospheric steadiness — the same conditions that let VATT achieve remarkably sharp images without relying on adaptive optics. Together, the three instruments represent decades of collaboration between the University of Arizona and international partners, including the Vatican Observatory.
Visiting Today
Public access to the summit facilities themselves is limited, both for safety and to protect ongoing research. The primary way for the public to engage with MGIO is through Discovery Park Campus in Thatcher/Safford, which has historically arranged seasonal guided tours up the mountain. Anyone hoping to visit should contact Discovery Park directly for the current tour schedule, since availability changes with weather, road conditions, and season. Visitors interested in the science behind the site can also learn more about the individual telescopes, including the Vatican Advanced Technology Telescope, as a complement to any observatory tour.