Gemini Observatory Provides Complete Coverage of the Sky

Gemini North Observatory
The Frederic C. Gillett Gemini North telescope with its vents open at sunset on Mauna Kea.

Gemini Observatory/AURA/NSF 

Ever since the year 2000, astronomers have used two unique telescopes that give them a peek at practically any part of the sky they wish to explore. These instruments are part of the Gemini Observatory, named for the Gemini constellation. They comprise an astronomy institution with twin 8.1-meter telescopes located in North and South America. Their construction began in the mid-1990s, guided by scientists from around the world.

The observatory's country partners are Argentina, Brazil, Canada, Chile, Korea, and the United States, under the aegis of the Association of Universities for Research in Astronomy, Inc. (AURA), under an agreement with the National Science Foundation. Each country has a national Gemini Office to coordinate participation. It's also part of the National Optical Astronomy Observatories (NOAO) consortium.

Both telescopes cost $184 million to build, and about $16 million per year for ongoing operations. In addition, $4 million a year are allocated for instrument development.

Key Takeaways: Gemini Observatory

  • Gemini Observatory is really one institution with two telescopes: Gemini North is located on Mauna Kea on the Big Island of Hawai'i and Gemini South is on Cerro Pachon in Chile.
  • The two telescopes together can study nearly the entire sky (except for two small areas at the celestial poles).
  • The Gemini telescopes use instruments and cameras, plus adaptive optics systems. 
  • Gemini Observatory can study anything from solar system objects to planets around other stars, starbirth, star death, and galaxies out to the limits of the observable universe.

One Observatory, Two Telescopes

The Gemini Observatory has historically been called "one observatory, two telescopes." Both were planned and built on high-altitude mountains to provide clear seeing without atmospheric distortion that plagues telescopes at lower altitudes. Both telescopes are 8.1 meters across, each containing a single-piece mirror fabricated at the Corning glass works in New York. These flexible reflectors are nudged by a system of 120 "actuators" that gently shape them for astronomical observations.

Gemini Observatory North with laser guide star system operating.
Gemini North with its laser system creating guide stars for adaptive optics. Gemini Observatory 

Each telescope uses these adaptive optics systems and laser guide stars, which help correct for atmospheric motions that cause starlight (and light from other objects in the sky) to be distorted. The combination of high-altitude location and cutting-edge technology gives Gemini Observatory some of the best astronomical views on Earth. Together, they cover nearly the entire sky (except for regions around the north and south celestial poles).

Gemini North on Mauna Kea 

The northern half of the Gemini Observatory is located on the Big Island of Hawai'i, at the summit of the Mauna Kea volcano. At an altitude of 4,200 meters (13,800 feet), this facility, officially named the Frederick C. Gillett Gemini Telescope (commonly called Gemini North), exists in a very dry, remote region. Both it and its twin are used by astronomers from the five member countries, plus researchers from the nearby University of Hawai'i. The U.S. Gemini office is located in Hilo, Hawai'i. It houses a staff of scientists, technical staff, outreach experts, and administrators. 

Gemini North with the Milky Way
Gemini North with the Milky Way overhead, and the lights of a town in the distance. The observatory is generally above the clouds, which blocks light from nearby cities. Gemini Observatory/Joy Pollard

The facility is open to astronomers who wish to do their work in person, but most take advantage of the telescope's remote operations capability. That means the telescope is programmed to do their observations and return the data to them when the observations are done. 

Gemini South at Cerro Pachón

The second pair of the Gemini twin telescopes is located on Cerro Pachón, in the Chilean Andes mountains. It's at an altitude of 2,700 meters (8,900 feet). Like its sibling in Hawai'i, Gemini South takes advantage of very dry air and good atmospheric conditions to observe the southern hemisphere skies. It was built about the same time as Gemini North and made its first observations (called first light) in 2000. 

Gemini South
Gemini South with its vents open at sunset. Gemini Observatory 

The Instruments of Gemini

The twin Gemini telescopes are outfitted with a number of instruments, including a set of optical imagers, plus other technology that dissect incoming light using spectrographs and spectrometers. These instruments provide data about distant celestial objects that are not visible to the human eye, particularly near-infrared light. The special coatings on the telescope mirrors make infrared observations possible, and help scientists study and explore such things as planets, asteroids, clouds of gas and dust, and other objects in the universe. 

Instrument support mechanism for Gemini telescopes.
Instruments are attached to the Gemini North and South telescopes using instrument support systems. This one, at Gemini South, has several instruments attached (the box-like structures). Gemini Observatory

The Gemini Planet Imager

One particular instrument, the Gemini Planet Imager, was built to help astronomers search out extrasolar planets around nearby stars. It began operations at Gemini South in 2014. The imager itself is a collection of observational instruments including a coronagraph, spectrograph, adaptive optics, and other parts that help astronomers locate planets around other stars. It has been in operation since 2013 and has been continually tested and improved. One of its most successful planet searches turned up the world 51 Eridani b, which lies about 96 light-years away from Earth. 

A polar ring galaxy.
Polar ring galaxy NGC 660 as see through Gemini Observatory's north telescope. Gemini Observatory 

Gemini's Celestial Discoveries

Since Gemini opened, it has peered into distant galaxies and studied the worlds of our own solar system. Among its most recent discoveries, Gemini North took a look at a distant quasar (an energetic galaxy) that had previously been observed by two other observatories: the Keck-1 on Mauna Kea and the Multiple-Mirror Telescope (MMT) in Arizona. Gemini's role was to focus on a gravitational lens that was bending the light from the distant quasar toward Earth. Gemini South has also studied distant worlds and their actions, including one that may have been kicked out of orbit around its star.

Other images from Gemini include a look at a colliding galaxy called a polar ring galaxy. This one is called NGC 660, and the image was taken from the Fredrick C. Gillett Gemini North telescope in 2012.


  • “Exiled Exoplanet Likely Kicked out of Star's Neighborhood.” » Circumstellar Disks,
  • Gemini Observatory,
  • “Gemini Observatory.” Gemini Observatory,
  • National Research Council Canada. “Gemini Observatory.” Construction Technology Updates, 27 Sept. 2018,
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Petersen, Carolyn Collins. "Gemini Observatory Provides Complete Coverage of the Sky." ThoughtCo, Feb. 17, 2021, Petersen, Carolyn Collins. (2021, February 17). Gemini Observatory Provides Complete Coverage of the Sky. Retrieved from Petersen, Carolyn Collins. "Gemini Observatory Provides Complete Coverage of the Sky." ThoughtCo. (accessed June 11, 2023).