The Reflecting Telescope

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In 1663, aged just 24, Aberdeenshire mathematician James Gregory published Optica Promota in London — setting out the world's first practical reflecting telescope design. Gregory never built one (Newton beat him to the first working reflector in 1668, and Hooke built the first Gregorian c. 1673), but his mirrors-not-lenses principle now underpins virtually every great observatory on Earth and in space — from the Hubble Space Telescope to the James Webb Space Telescope.