擁有觀測天體的望遠鏡及其附屬設備的機構。可以根據所要觀測的電磁波譜來劃分天文台。大多數天文台都是光學天文台，即它們是用來觀測電磁波譜中人眼可見的波段及其附近波段的輻射。有些天文台則是專門設置來發現那些能發出無線電波的天體，而另一些設置在人造地球衞星上的所謂軌道天文台，則配備有各種特殊的望遠鏡和檢測器，專門在地球大氣層以外研究發射像γ射線和X射線這種高能輻射的天體發射源。據説英國的巨石陣是早期的光學天文台。第一個使用儀器來精測天體方位的天文台可能是喜帕恰斯於西元前150年左右建於羅得島的天文台。1576年第谷在文島建立天文台。第一架用來研究天體的望遠鏡是伽利略於1609年製造的。18世紀時，赫瑟爾在英格蘭斯勞建造一座天文台，是由私人建造和管理的着名天文台。目前，世界上最大組的光學望眼鏡在夏威夷的冒納開亞山上和智利的（Cerro Tuldo），其他大型天文台包括阿雷西沃天文台、威爾遜山天文台、帕洛馬天文台和格林威治天文台。
observatory
Structure containing telescopes and secondary instruments for observing celestial objects. Observatories can be classified by the part of the electromagnetic spectrum they can receive. Most are optical, observing in and near the region of the visible spectrum. Some are equipped to detect radio waves; others (orbiting astronomical observatories) are earth satellites that carry special telescopes and detectors to study celestial sources of high-energy radiation (e.g., gamma rays, ultraviolet radiation, X rays) from above the atmosphere. Stonehenge may have been an early optical observatory. Perhaps the first observatory that used instruments to accurately measure the positions of celestial objects was built c. 150 BC by Hipparchus. The first notable premodern European observatory was that at Uraniborg, built for Tycho Brahe in 1576. Observatory House, in Slough, England, built and operated by the Herschels, was one of the technical wonders of the 18th century. Today, the world's largest groupings of optical telescopes are atop Mauna Kea, in Hawaii, and Cerro Tuldo, in Chile. Other major observatories include Arecibo Observatory, Mount Wilson Observatory, Palomar Observatory, and Royal Greenwich Observatory.
