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David Dunlap Observatory
Dunlap Observatory.jpg
The 74-inch (1.9 m) telescope at the David Dunlap Observatory
Organization University of Toronto (1935–2008)
Royal Astronomical Society of Canada (2009–2016)
City of Richmond Hill (2018-)
Location Richmond Hill, Ontario, Canada
Altitude 224 m (735 ft)
Weather 67% clear nights[1]
Established 31 May 1935
Website (1935-2008), (2009-2016), (2018-)
Telescope 1 1.88 m reflector
Telescope 2 0.6 m Cassegrain
Telescope 3 0.5 m Cassegrain

The David Dunlap Observatory (DDO) is an astronomical observatory site just north of Toronto, in Richmond Hill, Ontario. Formerly owned and operated by the University of Toronto, from its establishment in 1935 until 2008; the observatory is now owned and operated by the City of Richmond Hill providing 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. 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 July 31, 2019, the DDO was accepted by the National Historic Board as a National Historic Site of Canada.



David Dunlap Observatory Concept Sketch
Concept sketch of David Dunlap Observatory

The DDO owes its existence almost entirely to the efforts of one man, Clarence Chant. Chant had not shown an early interest in astronomy, but while attending University College, University of Toronto he became interested in mathematics and physics, eventually joining the university as a lecturer in physics in 1892. Over the next several years he worked as a schoolteacher and civil servant. During a later leave of absence he earned his PhD from Harvard University and did postdoctoral work in Germany.

Chant joined the Astronomical and Physical Society of Toronto in December 1892; it was eventually renamed the Royal Astronomical Society of Canada in 1902. Chant became president of the Society, serving between 1904 and 1907. Throughout the 1890s, Chant was concerned about how little the University did for astronomy, and in 1904 he proposed adding several undergraduate courses for fourth-year students, and six such courses were added to the 1905 calendar.

With courses now officially on the books, Chant started looking for a proper telescope. Previously the university had hosted the Toronto Magnetic and Meteorological Observatory, which had been run by the Meteorological Office of the Ministry of Marine and Fisheries. The observatory, built in 1840, had contained the high-quality 6-inch (150 mm) Cooke Refractor, but the Observatory was now surrounded by new university buildings, rendering it useless for astronomy. The Meteorological Office had already decided to abandon the site and turn the building over to the university, but they were taking the telescope with them to their new location at 315 Bloor Street West. Even if the university had been able to secure time on the instrument, which was highly likely, it was at this time quite a small instrument in comparison to those being built around the world.

The same problem of encroachment that had led to the observatory falling into disuse led Chant to conclude that there was no suitable location on the university grounds for a new observatory, and he started looking for off-campus sites. 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 the perfect location, a 10-acre (40,000 m2) plot of land near what is today Bathurst Street and St. Clair Avenue. The land had originally been set aside by the city for the Isolation Hospital, but this was never constructed and it now lay empty. 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.

Dunlap involvement

David Dunlap
David Alexander Dunlapes, about 1920

Chant then turned to the local business community in hopes of finding funding. Similar collaborations had been very successful in the United States, but Chant found an entirely different reception in Canada and nothing seemed forthcoming. His fortunes changed in 1921 when Chant delivered a public lecture on Comet 7P/Pons-Winnecke, which had recently been visible in Canada. One of the attendees was Hollinger Mines co-founder, lawyer David Dunlapes (1863–1924), who was bitten by the astronomy bug as a result of the lecture, and expressed an interest in Chant's efforts to build a large observatory. Before making any firm financial commitment, however, Dunlap died in October 1924 at age 61 (also see 70207 Davidunlap). Chant approached his widow, Jessie Dunlap, in late 1926 with the idea of erecting an observatory as a monument to her husband. Mrs. Dunlap promised to "keep it in [her] heart for consideration, for it appeals to me tremendously."

By this point the original site was well within the rapidly growing city's lit areas, and no longer suitable for astronomy. A site much further from the city was needed, to ensure it too would not be crowded out. The first site studied was outside Aurora, Ontario, but it was decided that it was too far from the university for casual travel. Another site near Hogg's Hollow was also studied, but was not easily accessible. The eventual site was selected while Chant was studying topographical maps with fellow astronomer Reynold Young, finding a suitable spot north of the city. The site was a short distance east of Yonge Street, and the Canadian Northern Ontario Railway line ran along the western end of the site. When Chant took Dunlap to see the site for the first time, she stated "this is the place!" and authorized its purchase for C$28,000.


Construction of Dunlap Observatory dome
Construction of the observatory's dome in Newcastle upon Tyne, after which it was dismantled and shipped to Richmond Hill
Mirror installation at observatory
Installation of the mirror
Queue at the Dunlap Observatory
Queue at the observatory in 1935, when guests were invited to inspect the telescope

Chant immediately started ordering a telescope, selecting a 74-inch (1.9 m) instrument from Grubb, Parsons and Company in England. This would make it the second-largest telescope in the world, second only to the 100-inch (2.5 m) instrument at Mount Wilson Observatory. It was, however, only slightly larger than the one that had recently gone into service for the Dominion Astrophysical Observatory in British Columbia, at 72 inches (1.8 m). 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 76-inch (1.9 m) mirror blank (the two outermost inches (5 cm) of the mirror are not used) was supplied by Corning Incorporated and cast in Pyrex from a batch of glass that Corning also used to produce the 200-inch (5.1 m) mirror for Palomar Observatory. Chant and Mrs. Dunlap attended the pouring of the mirror at the factory in Corning, NY in June 1933. The mirror was annealed, then shipped to Grubb-Parsons in England for polishing. The telescope was completed in time for the finished mirror's return in May 1935.

The official opening was on 31 May 1935, Chant's 70th birthday. The opening ceremony was attended by notables such as 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." Chant retired the same day and moved into Observatory House, the original pre-Confederation farmhouse (built in 1864 for Alexander Marsh and known also as Elms Lea Alexander Marsh) just to the south of the administration buildings, where he spent his remaining years. In May, 1939 the train carrying King George VI and Queen Elizabeth, the Queen Mother on their cross-Canada tour paused on the railway below the observatory, the largest telescope in the commonwealth.

Grubb-Parsons built four more 1.88-metre telescopes with similarities to the instrument in Richmond Hill: for Radcliffe Observatory near Pretoria, Mount Stromlo Observatory in Australia, Helwan Observatory in Egypt, and an observatory in Okayama Prefecture in Japan. The South African instrument was disassembled and moved to Sutherland, Northern Cape in the 1970s because of light pollution. The original telescope mirror at Helwan was replaced by Zeiss in 1997, and the telescope at Mount Stromlo was destroyed by fire in 2003. 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.

The three smaller domes on the top of the DDO administration building are used for smaller instruments. Soon after the observatory opened in 1935, a 50 cm Cassegrain reflector telescope was installed in the southern dome. The 6-inch (150 mm) Cooke Refractor had been out of use since the Meteorological Office had given it to Hart House, but it was little used and was moved into the northern dome in 1951 to be used by undergraduates. Much later, in 1965, a similar 60 cm Cassegrain was added to the central dome.


David Dunlap Observatory 1935
The view of David Dunlap Observatory in 1935. Observatory House is visible in the upper left.
Dunlap Observatory Administration Building
The administration building, with two of the observatory's telescopes built on top. The building's third dome is just out of sight behind the trees on the left.

From 1946 to 1951 the observatory director was Frank Scott Hogg, who was joined at the DDO by his wife Helen Sawyer Hogg. After her husband's death, Helen continued at the observatory, surveying globular clusters to gauge their distance, publishing a major catalog of variable stars in clusters. Her weekly 'With the Stars' column in the Toronto Star was published from 1951 to 1981. In 1959 and 1966 staff astronomer Sidney van den Bergh composed a database of dwarf galaxies known as the David Dunlap Observatory Catalogue.

In collaboration with the Department of Electrical Engineering, Dr. Donald MacRae established a radio astronomy observatory on the observatory grounds in 1956. The DDO work led to the 1963 measurement of the absolute flux density of Cassiopeia A at 320 MHz, a radiometric standard. The DDO also built an 18 m radio telescope in Algonquin Park in northern Ontario, co-locating it at the site of the larger Algonquin Radio Observatory. This instrument was actively used until 1991, when budget cuts led to it being abandoned. It was later used by a private group as part of a SETI project, Project TARGET, and has reported moved to a site outside Shelburne, Ontario.

In 1960 observatory operations formed the narrative framework of the NFB short film Universe. The film was nominated for the 33rd Academy Awards in the category of best documentary, short subject in 1961. 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. Universe featured future DDO director Donald MacRae and was narrated by Stanley Jackson.

Tom Bolton was hired as a postdoctoral fellow at the DDO in 1970. In 1971 he used data from the Uhuru X-ray observatory, and Naval Research Laboratory sounding rockets launched from White Sands Missile Range to find the optical companion star to the X-ray source Cygnus X-1. 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. Bolton observed the star HDE 226868 independently of the work by Louise Webster and Paul Murdin, at the Royal Greenwich Observatory, who could not prove that star was Cygnus X-1's optical companion. The high dispersion of the 74-inch (1.9 m) telescope's spectrograph, combined with the 74-inch (1.9 m) aperture was adequate to prove the star was the source of the X-ray emissions and that its behaviour was inconsistent with a normal eclipsing star.

Shifting locations

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. The Administration Building at the DDO headquartered the Astronomy Department until the 1960s, although the weekly department meetings continued to be held there until 1978. The main library was shifted downtown in 1983. The Cooke Refractor, now almost unused, was later donated to the Canada Science and Technology Museum in 1984.

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. Although some consideration was given to moving the telescope to a new site, in the end it was decided the funds would be better spent on a smaller instrument in a much better location. This led to the building of a 60 cm instrument at Las Campanas in Chile in 1971, creating the University of Toronto Southern Observatory (UTSO). It was at this location that University of Toronto telescope operator Ian Shelton discovered Supernova 1987A, the first supernova visible to the naked eye in more than 350 years. The UTSO was later closed in 1997 to re-allocate funds to a share of the Gemini Observatory, and the 60 cm telescope was moved to El Leoncito in Argentina, where the University has a 25% share in observation time. While University operations continued at the DDO, international observers used about 50% of observing time there.


The DDO main instrument was the second-largest telescope in the world when it began operation in 1935. Some of the largest telescopes in 1935 were:

# Name /
Image Aperture Altitude First
Special advocate
1 Hooker Telescope
Mount Wilson Obs.
100inchHooker.jpg 100 inch
254 cm
1742 m
(5715 ft)
1917 George Ellery Hale
Andrew Carnegie
2 David Dunlap Observatory Dunlap Observatory.jpg 74 inch
188 cm
224 m
(735 ft)
1935 Clarence Chant
3 Plaskett telescope
Dominion Astrophysical Obs.
Dominion Astrophysical Observatory front.jpg 72 inch
182 cm
230 m
(755 ft)
1918 John S. Plaskett
4 69-inch Perkins Telescope
Perkins Observatory
69 inch
175 cm
1931–1964 Hiram Perkins
5 61" reflector
Oak Ridge Observatory
61 inch
155 cm

Later in the 1930s, an 82 inch telescope was completed at McDonald Observatory in Texas. By the end of the next decade Dunlap's was still the fourth largest, due to the opening of the Hale Telescope in 1948. However, the telescope has remained the largest telescope in Canada until 1992, when the somewhat unique UBC-Laval LMT 2.65 m (104 in) came online. However, the LMT is a zenith telescope that only points up, using a liquid metal mirror.


The Observatory is featured multiple times in the NBC television series Hannibal. The administration building resembles the Baltimore State Hospital for the Criminally Insane. The Observatory is also featured on the Netflix production of The Umbrella Academy.

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