hut noted on site. 1847Signal Station built - finished 1848. 1857Signal Station altered, and in 1859, took its present form by 1864. 1858Demolition of windmill tower and construction of Observatory - finished 1859. 1876-8West wing built. Other alterations to residence in 1907. Most of the residence lath and plaster ceilings replaced by decorative pressed metal ceilings and matching cornices. 1907New staircase constructed in residence. 20th centuryMost observatory ceilings replaced by asbestos cement sheeting. - Addition of picture rails. 1982Wran Government decision to cease scientific work on site, Powerhouse Museum takes responsibility for management 1984-7DPWS manage major works to provide a museum of astronomy, exhibitions etc. November 1987Signal Station use as by Museum agreed to by Minister for Public Works. 1980sObservatory ceilings replaced with plaster-board; some floors replaced with particle board sheeting; some basement floors quarry tiled. 1985New staircase constructed in south west tower. 1987Garden re-landscaping/reinstatement to conform with Russell's plan of 1893, replanting with appropriate 19th century species (oleander, agaves, plumbago) by Royal Botanic Gardens Sydney staff. 1993Signal Station Messengers Cottage vacated and use as museum agreed in-principle by Treasurer in 11/1993. 1995Signal Station Messengers Cottage refurbished for use as offices by museum staff. All walls were plastered but have been progressively repaired and replaced over the years. 1997Many original instruments were conserved and restored to their former locations. 2008The Signal Station was restored and a replica flagstaff re-instated on the South rampart of the Fort wall for the Sydney Observatory 150th celebration. 2015Opened the East Dome which caters for people with disability. This won the National Trust's 2015 Heritage Award for Adaptive Reuse. Heritage listing As at 20 October 2005, the observatory is of exceptional significance in terms of European culture. Its dominant location beside and above the port town and, later, City of Sydney made it the site for a range of changing uses, all of which were important to, and reflected, stages in the development of the colony. These uses included: milling (the first windmill); defence (the first, and still extant, fort fabric); communications (the flagstaffs, first semaphore and first electric telegraph connection); astronomy, meteorology and time keeping. The surviving structures, both above and below ground, are themselves physical documentary evidence of 195 years' changes of use, technical development and ways of living. As such they are a continuing resource for investigation and public interpretation. The place has an association with an extensive array of historical figures