The David Dunlap Observatory

When the University of Toronto's downtown observatory could no longer function due to light pollution, the university identified a 19th-century farmstead in Richmond Hill as a suitable replacement site. Jessie Donalda Dunlap purchased the property and donated it to the university as a memorial to her husband, David Alexander Dunlap, an avid astronomer.

Canada's largest telescope

Construction was complete in 1935, with a dome housing a 74-inch reflector telescope that was, at the time, the second-largest in the world and remains the largest in Canada. From 1935 to 2007, the observatory was at the forefront of Canadian astronomical research; in 1972, astronomer Thomas Bolton used the telescope to confirm the existence of black holes, providing the first direct evidence that Cygnus X-1 was one.

From university property to historic site

The University of Toronto owned and operated the observatory until 2008, when it was acquired by the City of Richmond Hill, which now combines heritage preservation with public astronomy programming on the site. The David Dunlap Observatory was designated a National Historic Site of Canada in 2019.

Sources

• City of Richmond Hill — RHDDO History
• Parks Canada — David Dunlap Observatory National Historic Site of Canada

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