The Sydney Observatory is a heritage-listed meteorological station, astronomical observatory, function venue, science museum, and education facility located on Observatory Hill at Upper Fort Street, in the inner city Sydney suburb of Millers Point in the City of Sydney local government area of New South Wales, Australia. It was designed by William Weaver (plans) and Alexander Dawson (supervision) and built from 1857 to 1859 by Charles Bingemann & Ebenezer Dewar. It is also known as The Sydney Observatory; Observatory; Fort Phillip; Windmill Hill; and Flagstaff Hill. It was added to the New South Wales State Heritage Register on 22 December 2000. The site was formerly a defence fort, semaphore station, time ball station, meteorological station, observatory and windmills. The site evolved from a fort built on 'Windmill Hill' in the early 19th century to an observatory during the nineteenth century. It is now a working museum where evening visitors can observe the stars and planets through a modern Schmidt-Cassegrain telescope and an historic refractor telescope built in 1874, the oldest telescope in Australia in regular use. History Early use of the site The site of the Sydney Observatory has been a significant place in Sydney and has undergone a number of name changes. It was known as Windmill Hill in the 1790s when it was the site of the first windmill. After 1804 references are made to it as Fort Phillip or Citadel Hill, referring to the construction, but never completion, of a citadel on the site at Governor King's instruction for use in the case of an insurrection in Sydney. This was prompted by an influx of "Death or Liberty" Boys after the abortive 1798 uprising in Ireland, some of whom he believed to be of the most desperate character and cause for constant suspicion. Construction began but the citadel was not completed until Bligh had been installed in office. There were further discussions about a citadel during the Macquarie period but nothing eventuated beyond a half built powder magazine, Francis Greenway's first work after his appointment as civil architect in 1815. In 1797, early on during the European settlement of New South Wales, Australia, a windmill was built on the hill above the first settlement. Within ten years the windmill had deteriorated to the point of being useless; the canvas sails were stolen, a storm damaged the machinery, and already by 1800 the foundations were giving way. The