Editing David Dunlap Observatory (section)

{{About|the observatory in Richmond Hill, Ontario|research centre at the University of Toronto|Dunlap Institute for Astronomy & Astrophysics}}
{{Use Canadian English|date=January 2023}}
{{Use dmy dates|date=May 2022}}

{{Infobox observatory
| name = David Dunlap Observatory
| image = Richmond Hill David Dunlap Observatory 2023.jpg
| caption = The {{convert|74|in|m|adj=on}} telescope (left) and Administration Building (right) at the David Dunlap Observatory
| organization = [[University of Toronto]] (1935–2008) <br /> [[Royal Astronomical Society of Canada]] (2009–2016) <br /> [[City of Richmond Hill]] (2018–)
| location = [[Richmond Hill, Ontario|Richmond Hill]], Ontario, Canada
| coords = {{coord|43.8629|-79.4227|format=dms|region:CA-ON_type:landmark|display=inline,title}}
| altitude = 224 m (735 ft)
| weather = 67% clear nights<sup>[http://www.astro.utoronto.ca/DDO/prospective/weatherddo.html]</sup>
| established = 31 May 1935
| website = {{URL|richmondhill.ca/ddo}}
| telescope1_name = Telescope 1
| telescope1_type = 1.88 m reflector
| telescope2_name = Telescope 2
| telescope2_type = 0.6 m Cassegrain
| telescope3_name = Telescope 3
| telescope3_type = 0.5 m Cassegrain
| telescope4_name = 
| telescope4_type = 
| telescope5_name = 
| telescope5_type = 
| telescope6_name = 
| telescope6_type = 
| embedded        = {{designation list|embed=yes|designation1=Canada|designation1_offname =David Dunlap Observatory National Historic Site of Canada|designation1_date = {{start-date|31 July 2019}}}}
}}
The '''David Dunlap Observatory''' ('''DDO''') is an [[astronomy|astronomical]] [[observatory]] site in [[Richmond Hill, Ontario|Richmond Hill]], Ontario, Canada. Established in 1935, it was owned and operated by the [[University of Toronto]] until 2008. It was then acquired by the city of Richmond Hill, which provides a combination of heritage preservation, unique recreation opportunities and a celebration of the astronomical history of the site. Its primary instrument is a {{Convert|74|in|m|2|adj=on}} [[reflecting telescope|reflector telescope]], at one time the second-largest telescope in the world, and still the largest in Canada. Several other telescopes are also located at the site, which formerly also included a small [[radio telescope]]. The telescope was driven  by the vision of astronomer [[Clarence Chant]], shared by businessman [[David Alexander Dunlap]]{{snd}}whose family provided financial support after Dunlap's death in 1924. The scientific legacy of the David Dunlap Observatory continues in the [[Dunlap Institute for Astronomy & Astrophysics]], a research institute at the [[University of Toronto]] established in 2008.

The DDO is the site of a number of important scientific studies, including pioneering measurements of the distance to [[globular cluster]]s, providing the first direct evidence that [[Cygnus X-1]] was a [[black hole]], and the discovery that [[Polaris]] was stabilizing and appeared to be "falling out" of the [[Cepheid variable]] category.<ref>[http://www.aavso.org/observing/programs/pep/pepnewsletter/may1998/main.shtml Polaris – The Story Continues] {{Webarchive|url=https://web.archive.org/web/20070930024806/http://www.aavso.org/observing/programs/pep/pepnewsletter/may1998/main.shtml |date=30 September 2007 }} ''Photoelectric Photometry Newsletter'', American Association of Variable Star Observers, May 1998</ref> Located on a hill, yet still relatively close to sea level at {{convert|730|feet}} altitude, and now surrounded by urban settlement, its optical astronomy ability has been reduced as compared to other remote observatory sites around the world. On 31 July 2019, the DDO was accepted by the National Historic Board as a [[National Historic Site of Canada]].<ref>[https://www.canada.ca/en/parks-canada/news/2019/07/government-of-canada-announces-eight-new-national-historic-designations.html Government of Canada Announces Eight New National Historic Designations], Parks Canada news release, 31 July 2019</ref>