David Dunlap Observatory

David Dunlap Observatory

The 74 inch telescope at the David Dunlap Observatory
Alternative names	DDO
Named after	David Alexander Dunlap
Organization	University of Toronto
Observatory code	779
Location	123 Hillsview Dr, Richmond Hill, Ontario, Canada
Coordinates	43°51′44″N 79°25′21″W
Altitude	224 m (735 ft)
Weather	67% clear nights[1]
Established	31 May 1935
Website	astro.utoronto.ca/DDO/
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

The David Dunlap Observatory (DDO) is a large astronomical observatory site for the University of Toronto, located just north of the city in Richmond Hill, Ontario. 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 co-located at the site, which formerly included a small radio telescope as well. Located fairly close to sea level the site was never ideal for research purposes, and the encroachment of well-lit subdivisions have dramatically limited its capabilities. Nevertheless the DDO was used in a number of important 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.

History

Genesis

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 math and physics, eventually joining the University as a lecturer in physics in 1892. He joined the Astronomical and Physical Society of Toronto in December that year; 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 real 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 had contained the high-quality 6-Inch Cooke Refractor, but the Observatory building itself 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 on Bloor Street. Even had the University 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 ten-acre plot of land located 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 start of World War I put the project on hold, and in 1919 it was cancelled outright.

Dunlap involvement

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 local businessman David Dunlap, 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 sixty-one. 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 they 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. 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

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.

Chant immediately started ordering a telescope, selecting a 74-inch 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 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. The observatory building itself started construction, and the eighty-ton sixty-one foot copper dome arrived in 1933. The administration building, a few hundred feet from the main observatory, also started construction. The telescope was installed while work on the mirror continued, and was completed in time for the mirror to arrive in May 1935.

The official opening was on 31 May 1935, Chant's 70th birthday. The opening ceremony was attended notables such as Sir Frank Dyson, former Astronomer Royal, and former Prime Minister 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 just to the south of the administration buildings, where he spent his remaining years.

The three smaller domes on the top of the administration building were also filled with smaller instruments. Soon after the observatory opened in 1935, a 50 cm Cassegrain reflector telescope was installed in the southern dome. The 6-inch Cooke Refractor had been out of use since the Met Office had given it to Hart House, but it was little used and was moved into the north dome in 1951 to be used by undergraduates. Much later, in 1965, another similar 60 cm 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 Dr Hogg's death, Helen continued at the observatory, surveying globular clusters to gauge their distance. 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 MacRae established a radio astronomy observatory on the observatory grounds in 1956. The DDO work led to the precise determination of the absolute flux density of Cassiopeia A at 320 MHz, a radiometric standard as important today as it was when it was reported in 1963. 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 recently been 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 Douglas Rain, who went on to act as the voice of HAL 9000 in 2001.

University of Toronto Professor Tom Bolton was hired at the DDO in 1970. In 1971 he used data from the Uhuru (satellite) 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. The X-ray telescopes had a certain degree of accuracy, but optical-wavelength studies of possible optical companions were required to eliminate a shortlist of many stars in the same area of sky. Bolton was building on tentative research from J.F. Dolan, an astronomer from San Diego State University who could not conclude the star HDE 226868 was Cygnus X-1's optical companion. The high dispersion of the 74-inch telescope's spectrograph, combined with the 74-inch aperture was adequate to prove the star was the source of the X-ray emissions and that its behavior 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 National Science 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. It was at this location that UofT astronomer Ian Shelton spotted SN 1987A. The site was later closed in 1997 in favor of moving those 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.

Current status, potential closure and sale

Today, light pollution from the huge tracts of subdivisions around the site have reduced the telescope's effectiveness as a photographic instrument. In 1989 the telescope's celestial observations were changed over from photographic plates to charge-coupled devices. Work continues on observation of active galactic nuclei and some spectroscopy with 100 mm and 1800 mm diffraction gratings. Professor Bolton's local dark-sky movement led to the use of a particular type of lighting better able to be filtered out with ease.

In September 2007, the University stated it was planning on selling the property due to light pollution. 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 ha of land in the midst of a huge subdivision area is expected to fetch $100 million. The move has been called a 'cash grab' by local politicians, who hope to be deeded the land for the park-starved area.

References

• The Legacy Continues:C. A. Chant and the David Dunlap Observatory, C. H. Russell, Journal of the Royal Astronomical Society of Canada, vol.93, no.1, February 1999
• A Memorial Tribute: Donald Alexander MacRae (1916-2006), E.R. Seaquist, Professor Emeritus, Department of Astronomy and Astrophysics, University of Toronto
• Astronomy and Astrophysics; A Short History of the Department and Observatory

Further reading

• The Cold Light of Dawn: A History of Canadian Astronomy, Richard A. Jarrell, University of Toronto Press, 1988, ISBN 978-0802026538

External links

• David Dunlap Observatory
• David Dunlap Observatory Clear Sky Clock forecasts of observing conditions.
• Save The David Dunlap Observatory Website