Hooke produces a reflecting telescope based on the Gregorian design. 1684 — Christiaan Huygens publishes "Astroscopia Compendiaria" in which he described the design of very long aerial telescopes. 1720 — John Hadley develops ways of aspherizing spherical mirrors to make very accurate parabolic mirrors and produces a much improved Gregorian telescope 1721 — John Hadley experiments with the neglected Newtonian telescope design and demonstrates one with a 6-inch parabolic mirror to the Royal Society. 1730s — James Short succeeds in producing a Gregorian telescopes to true paraboloidal primary and ellipsoidal secondary design specifications. 1733 — Chester Moore Hall invents the achromatic lens. 1758 — John Dollond re-invents and patents the achromatic lens. 1783 — Jesse Ramsden invents his eponymous eyepiece. 1803 — The "Observatorio Astronómico Nacional de Colombia (OAN)" is inaugurated as the first observatory in the Americas in Bogotá, Colombia. 1849 — Carl Kellner designs and manufactures the first achromatic eyepiece, announced in his paper "Das orthoskopische Ocular". 1857 — Léon Foucault improves reflecting telescopes when he introduced a process of depositing a layer of silver on glass telescope mirrors. 1860 — Georg Simon Plössl produces his eponymous eyepiece. 1880 — Ernst Abbe designs the first orthoscopic eyepiece (Kellner's was solely achromatic rather than orthoscopic, despite his description). 1897 — Largest practical refracting telescope, the Yerkes Observatorys' 40 inch (101.6 cm) refractor, is built. 1900 — The largest refractor ever, Great Paris Exhibition Telescope of 1900 with an objective of 49.2 inch (1.25 m) diameter is temporarily exhibited at the Paris 1900 Exposition. 1910s — George Willis Ritchey and Henri Chrétien co-invent the Ritchey-Chrétien telescope used in many, if not most of the largest astronomical telescopes. 1930 — Bernhard Schmidt invents the Schmidt camera. 1932 — John Donovan Strong first “aluminizes" a telescope mirror a much longer lasting aluminium coating using thermal vacuum evaporation. 1944 — Dmitri Dmitrievich Maksutov invents the Maksutov telescope. 1967 — The first neutrino telescope opened in Africa. 1970 — The first space observatory, Uhuru, is launched, being also the first gamma-ray telescope. 1975 — BTA-6 is the first major telescope to use an altazimuth mount, which is mechanically simpler but requires computer control for accurate pointing. 1990 — Hubble Space Telescope (HST) was launched into low Earth orbit 2000 CE to 2025 CE 2003 — The Spitzer Space Telescope (SST), formerly the Space Infrared Telescope Facility (SIRTF), is an infrared space observatory launched in