The Gemini Observatory is an astronomical observatory consisting of two 8.19-metre (26.9 ft) telescopes, Gemini North and Gemini South, which are located at two separate sites in Hawaii and Chile, respectively. As of 2017, the twin Gemini telescopes provide almost complete coverage of both the northern and southern skies. They are currently among the largest and most advanced optical/infrared telescopes available to astronomers. (See List of largest optical reflecting telescopes).
The Gemini telescopes house a suite of modern instruments, offer superb performance in the optical and near-infrared, and employ sophisticated adaptive optics technology to compensate for the blurring effects of the Earth's atmosphere. Gemini is a world-leader in wide-field adaptive optics assisted infrared imaging, and has recently commissioned the Gemini Planet Imager, an instrument that allows researchers to directly image and analyze exoplanets that are a millionth as bright as the host star around which they orbit. Gemini continues to support research in almost all areas of modern astronomy, including the Solar System, exoplanets, star formation and evolution, the structure and dynamics of galaxies, supermassive black holes, distant quasars, and the structure of the Universe on the largest scales.
Past participants in the Gemini Observatory include Australia and the United Kingdom. The UK dropped out of the partnership at the end of 2012 and the Gemini Observatory has responded to the loss of funding by significantly reducing its operating costs, streamlining its operations, and implementing energy savings measures at each site. Both telescopes are also now operated remotely from Base Facility Operations centers in Hilo, Hawaii, and La Serena, Chile.
The "Gemini North" telescope, officially called the Frederick C. Gillett Gemini Telescope is located on Hawaii's Mauna Kea, along with many other telescopes. That location provides excellent viewing conditions due to the superb atmospheric conditions (stable, dry, and rarely cloudy) above the 4,200-metre-high (13,800 ft) dormant volcano. It saw first light in 1999 and began scientific operations in 2000.
The "Gemini South" telescope is located at over 2,700 metres (8,900 ft) elevation on a mountain in the ChileanAndes called Cerro Pachón. Very dry air and negligible cloud cover make this another prime telescope location (again shared by several other observatories, including the Southern Astrophysical Research Telescope (SOAR) and Cerro Tololo Inter-American Observatory). Gemini South saw first light in 2000.
Together, the two telescopes cover almost all of the sky except for two large regions near the celestial poles: Gemini North cannot point north of declination +89 degrees, and Gemini South cannot point south of declination −89 degrees.
Both Gemini telescopes employ a range of technologies to provide world-leading performance in optical and near-infrared astronomy, including laser guide stars, adaptive optics, multi conjugate adaptive optics, and multi-object spectroscopy. In addition, very high-quality infrared observations are possible due to the advanced protected silver coating applied to each telescope's mirrors, the small secondary mirrors in use (resulting in an f16 focal ratio), and the advanced ventilation systems installed at each site.