From its launch in 1948 until 1975, the largest telescope in the world was the Hale Telescope on Palomar Mountain in southern California, a giant Newtonian reflector with a mirror 200 inches (5 meters across). Even when Hale was displaced by the 6-meter Russian BTA-6 telescope, it remained the most effective large-aperture telescope in the world because the Russian behemoth suffered from many design flaws and operational problems.
But in the early 1990’s, Hale was bumped once and for all from the top of the telescope world. That’s when the first of the two Keck telescopes, each with 10-meter mirrors, became operational at an observatory on Mauna Kea. Since then, ground based astronomy has entered a new period of rapid innovation and growth as larger and more sophisticated instruments come online, most with adaptive optics and systems to combine the light from more than one mirror. The Keck scopes are still #2 on the list, and were only recently bumped by a slightly larger scope called the Gran Telescopio Canarias. If you are having trouble keeping track of the world’s largest telescopes, the infographic above will help you sort out which is which.
The five largest operating telescopes are:
1. Gran Telescopio Canarias (10.4 meter objective mirror). Telescope is located at Roque de los Muchachos Observatory, Canary Islands, Spain
2. Keck I and Keck II (each with 10.0 meter objective). Both scopes are atop Mauna Kea in Hawaii.
3. South African Large Telescope (9.2 meter objective). Operated by the South African Astronomical Observatory, this is the largest-aperture telescope to date in the southern hemisphere.
4. Hobby-Eberly Telescope (9.2 meter objective). Located at McDonald Observatory in Texas.
5. Large Binocular Telescope (2 x 8.4 m mirrors). At Mount Graham Observatory in Arizona. This telescope can be operated to deliver the same performance as a single 11.9 meter telescope.
Many larger scopes are in the works. The next to come online will be the Giant Magellan Telescope at Las Campanas Observatory in Chile in 2020. It will have seven 8.4 meter mirror segments that combine to operate as a single 24.5 meter telescope. In 2022, the Thirty Meter Telescope may be completed on Mauna Kea, though it is still in a preliminary stage. In the same year, European astronomers look forward to opening the European Extremely Large Telescope at Cerro Armazones in Chile. It will have a mirror that’s an astounding 39.3 meters in diameter. Just the secondary mirror of this beast will span 4.2 meters!