The Royal Observatory of Belgium, officially known in French as the Observatoire Royal de Belgique, and in Dutch as the Koninklijke Sterrenwacht van België, is situated in Uccle (Ukkel in Dutch) since 1890. It was first established in Saint-Josse-ten-Noode in 1826 by William I under the impulse of Adolphe Quetelet. It was home to a 100 cm diameter aperture Zeiss reflector in the first half of the 20th century, one of the largest telescopes in the world at the time.