From Galileo’s 1.5 cm telescope in 1609 to the current champion, the 10.4 metre Gran Telescopio Canarias which entered service in 2009, the evolution of ground-based optical telescopes has been four centuries of demonstration that “there’s no substitute for aperture”. Now that adaptive optics have largely eliminated the atmospheric distortions that previously afflicted large aperture telescopes, the only limit seems to be the budget available to build ever larger instruments, with the 39.3 metre European Extremely Large Telescope under construction and scheduled for first light in 2027.
It’s interesting how, in the past, some telescopes held the record for largest over long periods of time. William Herschel’s 1.26 metre telescope was largest in the world from 1789 through 1845 (56 years) when it was succeeded by William Parsons’ 1.83 metre Leviathan which held the record until 1917 (72 years) when the 2.54 metre Hooker Telescope on Mount Wilson claimed the record, which it held until the 5.08 metre Hale Telescope at Palomar Observatory was inaugurated in 1948 (31 years). The Hale telescope was exceeded in aperture in 1976 by the Soviet BTA-6 6 metre telescope (28 years), but that instrument was plagued by problems and was never scientifically productive. The modern era of large aperture telescopes was inaugurated by the 10 metre Keck Telescope in 1993, 45 years after the Hale.
Scott Manley trips over the humble apostrophe in titling this video.