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.

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.

The Meteorological Office had already decided to abandon the site and turn the building over to the university, but they were taking the telescope to their new location at 315 Bloor Street West.

While looking, he started getting quotes for a new instrument from Warner & Swasey in Cleveland, Ohio, who had provided the mount for the recently opened Dominion Observatory in Ottawa.

In 1910 Chant finally found a suitable location, a 10-acre (4.0 ha) plot of land near what is today Bathurst Street and St. Clair Avenue.

Chant convinced the city to become involved in the Royal Astronomical Observatory, but the outbreak of World War I put the project on hold, and in 1919 it was cancelled outright.

Chant approached his widow, Jessie Dunlap, in late 1926 with the idea of erecting an observatory as a monument to her husband.

The eventual site was selected while Chant was studying topographical maps with fellow astronomer Reynold K. Young, finding a suitable spot north of the city.

The observatory building itself started construction, and the eighty-ton sixty-one-foot (18.6 m) copper dome was built by Grubb and Parsons in 1932 and arrived in 1933.

The administration building, a few hundred feet from the main observatory, also started construction and designed by Mathers & Haldenby Architects.

The opening ceremony was attended by notables including Sir Frank Dyson, former Astronomer Royal, and former Prime Minister William Lyon Mackenzie King, who praised the Observatory as "a gift to science all over the world".

[12] A 1.93-metre Grubb-Parsons telescope at Haute-Provence Observatory with a higher-resolution spectrograph was used to discover an extrasolar planet orbiting the star 51 Pegasi in 1995.

In 1959 and 1966 staff astronomer Sidney van den Bergh composed a database of dwarf galaxies known as the David Dunlap Observatory Catalogue.

Universe was shown at the 1964 New York World's Fair where it was seen by Stanley Kubrick and Arthur C. Clarke, who were starting work on the film that eventually became 2001: A Space Odyssey.

Those X-ray telescopes had a certain degree of accuracy, but follow-up optical-wavelength studies of possible companions were required to eliminate a shortlist of many stars in the same area of sky.

[21][22] With the rapid growth of university funding in the 1960s more offices were being built in the downtown campus, and with the opening of the McLennan Labs more and more of the department moved into the new facilities.

[3] The main reflector at the DDO remained a major instrument into the 1960s, but in the end even the "remote" location Chant had selected was being encroached on by urban sprawl.

This led to the building of a 60-centimetre (24 in) instrument at Las Campanas in Chile in 1971, creating the University of Toronto Southern Observatory (UTSO).

[27] The university's governing council voted on the issue during the week of 1 November 2007, and agreed to sell the site to the highest bidder.

The 75 hectares (190 acres) of land in the midst of a very large subdivision area was expected to fetch $100 million, some of which the university planned to use to found a Dunlap Institute to continue astronomical research.

[35] The Town proceeded with a number of public meetings and reports in late 2009 to craft guidelines for the conservation, planning and design of the property.

[36] On 15 April 2010, stemming from an incident on the property in November 2009, Corsica Development Inc. pleaded guilty in York Region court to 17 counts of cutting a tree without a permit and was issued a fine of $44,880.

[38] In January 2009, Corsica published the website observatoryhill.ca describing the property, stating, "[We] are in the process of looking for an astronomy club to occupy the observatory and welcome proposals for consideration.

"[39] On 22 April 2009, Corsica and the Royal Astronomical Society of Canada announced an agreement allowing the RASC to provide public education and outreach programs at the observatory, and to operate the 1.88m telescope.

[40] On 14 June, the RASC Toronto Centre published the website www.theddo.ca,[41] to make tickets available for public astronomy nights at the observatory starting on 18 July.

[45] A further legal appeal by the Richmond Hill Naturalists to preserve the entire site from development was launched in August 2013[46] and was ultimately unsuccessful.

[50][51] In April 2015, Corsica (having changed their name to DG Group) announced plans to transfer ownership of the observatory buildings to the RASC.

Despite RASC-TC's status as a registered charitable corporation, some parties to the 2012 five-party OMB settlement argued that the donation placed the future of the observatory in doubt, because RASC was not a government agency.

In October 2016, the Town of Richmond Hill approved a master plan to turn 40 hectares (99 acres) of the Observatory lands into a "destination park", for astronomical outreach programs, while adding recreational amenities such as walking paths, 4 tennis courts, an amphitheatre and a low-light level "Star Path" self-illuminating pathway.