Around the world, about thirty observatories have dedicated at least one telescope to the study of the Sun. Given the atmospheric turbulence, it is almost impossible to use instruments over one meter in diameter unless you have a high altitude site or install adaptive optics. Also for the time being, the largest solar telescope is 1.60 m in diameter but China is considering the construction of a solar telescope of 5 to 8 m in diameter.
Among the largest operational instruments are NOAA’s US National Solar Observatory (including the 1.60 m diameter McMath-Pierce solar tower telescope installed at Kitt Peak in Arizona, which has a heliostat primary mirror measuring 2.1 m of diameter as well as the Dunn and Evans telescopes of Sacramento Peak), the Big Bear Solar Observatory (BBSO, 1.60 m in diameter) installed in California, the Gregor solar telescope of 1.50 m installed at the Observatory of Teide where is also installed the 90 cm Franco-Italian Thémis solar telescope and the 70 cm Vacuum Tower Telescope (MTB), the Mauna Loa Observatory MLSO in Hawaii, the HAO High Altitude On-Board Observatory and the Swedish Solar Telescope (SST 1 m). All other instruments are smaller in diameter (15-70cm).
Several large solar telescopes are also under construction or the project is planned as the European Solar Telescope (EST) of more than 4 m in diameter which should be installed in the Canary Islands probably after 2020 but currently it is radio silence.
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