David Dunlap Observatory

David Dunlap Observatory

The 74-inch (1.9 m) telescope (left) and Administration Building (right) at the David Dunlap Observatory
Alternative names	DDO
Named after	David Alexander Dunlap
Organization	University of Toronto (1935–2008) Royal Astronomical Society of Canada (2009–2016) City of Richmond Hill (2018–)
Observatory code	779
Location	Richmond Hill, Ontario, Canada
Coordinates	43°51′46″N 79°25′22″W / 43.8629°N 79.4227°W / 43.8629; -79.4227
Altitude	224 m (735 ft)
Weather	67% clear nights[1]
Established	31 May 1935
Website	astro.utoronto.ca/DDO (1935–2008), www.theddo.ca (2009–2016), richmondhill.ca/ddo (2018–)
Telescopes
Telescope 1 1.88 m reflector Telescope 2 0.6 m Cassegrain Telescope 3 0.5 m Cassegrain
Location of David Dunlap Observatory
Related media on Commons
National Historic Site of Canada
Official name	David Dunlap Observatory National Historic Site of Canada
Designated	31 July 2019 (2019-07-31)
[edit on Wikidata]

The David Dunlap Observatory (DDO) is an astronomical observatory site in 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 74-inch (1.88 m) 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 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 clusters, 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.^[1] Located on a hill, yet still relatively close to sea level at 730 feet (220 m) 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.^[2]