page_title: Primary mirror
section_title: Superlative primary mirrors
hierarchical_section_title: Primary mirror / Superlative primary mirrors
caption_attribution_description: English: This artist's rendering shows the huge segmented primary mirror of the ESO Extremely Large Telescope (ELT). Contracts for the manufacture of the mirror segments were signed on 30 May 2017 at a ceremony at ESO’s Headquarters near Munich. The German company SCHOTT will produce the blanks of the mirror segments, and the French company Safran Reosc will polish, mount and test the segments. The contract to polish the mirror blanks is the second-largest contract for the ELT construction and the third-largest contract ESO has ever awarded.
context_page_description: A primary mirror is the principal light-gathering surface of a reflecting telescope.
context_section_description: The largest optical telescope in the world as of 2009 to use a non-segmented single-mirror as its primary mirror is the 8.2 m (26.9 ft) Subaru telescope of the National Astronomical Observatory of Japan, located in Mauna Kea Observatory on Hawaii since 1997; however, this is not the largest diameter single mirror in a telescope, the U.S./German/Italian Large Binocular Telescope has two 8.4 m (27.6 ft) mirrors (which can be used together for interferometric mode). Both of these are smaller than the 10 m segmented primary mirrors on the two Keck telescope. The Hubble Space Telescope has a 2.4 m (7 ft 10 in) primary mirror.
  Radio and submillimeter telescopes use much larger dishes or antennae, which do not have to be made as precisely as the mirrors used in optical telescopes. The Arecibo Observatory uses a 305 m dish, which is the world largest single-dish radio telescope fixed to the ground. The Green Bank Telescope has the world's largest steerable single radio dish with 100 m in diameter. There are larger radio arrays, composed of multiple dishes which have better image resolution but less sensitivity.
caption: Artists's Rendering of the primary mirror of the ELT.[3]
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