David Dunlap Observatory
The David Dunlap Observatory 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 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 Dunlapwhose 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 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 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.
History
Genesis
The DDO owes its existence almost entirely to the efforts of 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 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 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 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 a suitable location, a 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 lack of funds and the outbreak of World War I put the project on hold, and in 1919 it was cancelled outright.
Dunlap involvement
Knowing that similar funding collaborations had been very successful in the United States, Chant turned to the local business community. To promote his plan, Chant often concluded public lectures with a pitch to the audience for a larger observatory for Toronto; this included a 1921 talk on Comet 7P/Pons-Winnecke, which had recently been visible in Canada. One of the attendees was Hollinger Mines co-founder, lawyer David Dunlap, who expressed an interest in Chant's efforts to build a large observatory. However, before making any financial commitment, Dunlap died in October 1924 at age 61 . In late 1926, Chant wrote to his widow, Jessie Dunlap, with the idea of erecting an observatory as a monument to her husband. Mrs. Dunlap promised to "keep it in heart for consideration, for it appeals to me tremendously."By this point the chosen site was within the rapidly-growing city, and not suitable for astronomy due to both light pollution. A site much further from the city was needed, to ensure it too would not be crowded out, as well as to reduce the impact of moisture-filled air and fog from Lake Ontario. 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 K. 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. It was on Lot 42 on what was Alexander Marsh's farm and orchard. In 1930, when Chant took Dunlap to see the site for the first time, she stated "this is the place!" and authorized its purchase for .
Construction
Chant immediately ordered a telescope, selecting a instrument from Grubb, Parsons and Company in England. This would make it the second-largest telescope in the world, second only to the 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. The eighty-ton sixty-one-foot copper dome and cylindrical walls of the observatory building were constructed by the Cleveland Bridge and Engineering Co. of Darlington, UK, with the mechanical parts supplied by Grubb & Parsons. The parts of the building and telescope arrived in Toronto in 1933 and were reassembled on site. The administration building, a few hundred feet from the main observatory, was designed by Toronto architectural firm Mathers & Haldenby. The mirror blank was supplied by Corning Incorporated and cast in Pyrex from a batch of glass that Corning also used to produce the mirror for Palomar Observatory. Chant and Mrs. Dunlap attended the pouring of the mirror at the factory in Corning, New York 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 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". Reynold K. Young was named the first director of the DDO. Chant retired the same day and moved into Observatory House, the original pre-Confederation farmhouse 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 at the top of the DDO administration building are used for smaller instruments. Soon after the observatory opened in 1935, a Cassegrain reflector telescope was installed in the southern dome. A large vacuum tank was constructed, then used to aluminize the 74-inch mirror in 1941. The 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. In 1965, a similar Cassegrain was added to the central dome.
Operations
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, 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 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 National Film Board 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 telescope's spectrograph, combined with the 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.