The 75th Anniversary of the David Dunlap Observatory


Date: May 31, 2010

Title: The 75th Anniversary of the David Dunlap Observatory


Podcaster: Toronto Centre of the Royal Astronomical Society of Canada

Organization: Toronto Centre of the Royal Astronomical Society of Canada

Description: The David Dunlap Observatory celebrates its 75th anniversary; also conservation of historic observatories is discussed.

Bio: All of our presenters are council members of the Toronto Centre of the Royal Astronomical Society of Canada.

Karen Mortfield is our public affairs co-ordinator.

Dr. Ralph Chou is the president, and also a professor at the University of Waterloo school of optometry.
Brenda Shaw is a councillor and one of our volunteers at the David Dunlap Observatory.

Eric Briggs is the secretary of the Toronto Centre and also a contractor with the Spitz planetarium company.

The Toronto Centre of the RASC is grateful for the assistance we’ve received from Metrus Developments and the Town of Richmond Hill, Ontario.
You can find out more about the David Dunlap Observatory, its history, and our 2010 schedule of events at our website,
The RASC Toronto Centre’s website is

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May 31, 2010 celebrates the 75th anniversary of the David Dunlap Observatory in Richmond Hill, Ontario, Canada, located just north of Toronto. At the time it opened on May 31, 1935 it was the 2nd largest in the world, and the 74-inch diameter telescope remains the largest optical telescope in Canada.

The existence of the David Dunlap Observatory is largely due to the efforts of one man, Clarence Chant. Professor Chant campaigned for the better part of thirty years for a large observatory near Toronto. The existence of the Royal Astronomical Society of Canada is also largely due to Professor Chant. David Dunlap was a wealthy member of the Society, and after his death Professor Chant met with Mrs. Dunlap, who agreed to fund the observatory as a memorial to her husband.

The 74-inch telescope was manufactured by the Grubb-Parsons company in England. The Parsons part of the company comes from Charles Parsons, whose father was the Earl of Rosse in Ireland, who built a 72-inch telescope in the mid-19th Century called the Leviathan of Parsonstown, that was the largest telescope in the world for decades. The telescope mirror for the DDO was manufactured by the Corning Glass Company in New York, as a test article for the larger 200-inch mirror for Palomar Mountain that was made a short time later. So the DDO was built by the best.

The spectrograph at the DDO was used to independently confirm the first Black Hole, Cygnus X-1 in 1972. That’s the most well-known accomplishment of the DDO, but many other research projects have been conducted here. For example, studies of how Polaris varies its brightness. The first blazar, BL Lacertae, was co-discovered by astronomers at DDO. Helen Sawyer Hogg discovered a nova in the globular cluster Messier 14 on photographic plates she exposed at DDO, in the process of a long project to determine the distances to globular clusters to determine the scale of the universe. Astronomers trained at DDO went on to do good work elsewhere. For example, Dr. Wendy Freedman and Barry Madore, (Wendy is the director of the Observatories of the Carnegie Institution) both did their first astronomical work at the DDO.

What happened at the Dunlap Observatory is that the University of Toronto found that most of their astronomy faculty were doing work away from the observatory they owned. The University had another observatory on Cerro (See-Arrow) Las Campanas in Chile for a while, but nowadays some of their astronomers are using the much bigger Canada-France-Hawaii Telescope, Hubble Space Telescope, the Gemini telescopes and so on. Also, the urban areas around the City of Toronto have grown up around the observatory and although some pioneering work has been done to reduce the impact of light pollution, the DDO is not a dark sky site any more. Rather than leasing the observatory to a community group themselves, the U of T sold the Dunlap Observatory property to a developer, who has since leased the observatory dome back to the Toronto Centre of the Royal Astronomical Society of Canada – that’s us. The University then used the proceeds from the sale to start a new Dunlap Institute for Astrophysics, which is expected to be a centre for cutting-edge science that will continue to work with the world’s largest telescopes. Since purchasing the DDO site, the developer has also participated in a series of consultations with the Town of Richmond Hill and community groups concerned with how they plan to use the rest of the property. We think those consultations are far from over, and we’re glad to have a part to play in the process. In the meantime, we held a successful series of public observatory nights last year, and we’ve begun a new season in 2010.

The Toronto Centre of the Royal Astronomical Society of Canada today is the same kind of organization it was when Clarence Chant helped to bring the Society together a hundred years ago: a combination of amateurs and professional astronomers. Several of our members were trained at the DDO when they were in University, and several more have been trained to operate the telescope during the last year. The RASC has helped operate public astronomy outreach activities at the DDO since it opened 75 years ago, and several of our members have gone on to be on the staff of the observatory over the years, so many of our younger members were inspired to pursue professional astronomy careers. We’re continuing this work, doing science outreach with schools, to communicate astronomy which is part of the provincial school curriculum.

Earlier this year we had a visit from Dean Regas, an astronomer from the Cincinnati Observatory Center. Cincinnati Observatory was originally opened by former President John Quincy Adams in 1843, making their site almost a century older than ours, although their observatory has moved a couple of times since then. The Cincinnati Observatory land is still owned by the University of Cincinnati, but for a while in the 1990s they considered selling the land for development. The Cincinnati Observatory Center came along and leased the observatory from the University, so they saved it. Now it’s used more for public outreach in astronomy than hard research. After meeting us and having a look through our telescope, Dean told us he feels like we’re at the stage he and his friends were at about ten years ago.

One of the other historic observatories we’ve been communicating with is Mount Wilson Observatory near Pasadena. When the DDO was completed in 1935, the telescope here was the second-largest in the world, and the largest was on Mount Wilson. It’s still there, but for several years in the 1980s and early 1990s the 100-inch telescope at Mount Wilson was closed and the funds used to operate it were re-allocated to new telescopes elsewhere by the Carnegie Institution, which used to run Mount Wilson. Within a few years, Carnegie turned operations on the mountaintop over to the Mount Wilson Institute, a 501(c)(3) non-profit corporation. The 100-inch Mount Wilson telescope was brought back into service in 1992, in time to record Comet Shoemaker-Levy 9 colliding with Jupiter. The 100-inch telescope is still used for research projects, but a smaller 60-inch telescope that was built in 1908 is used for public outreach programs. The biggest threat to Mount Wilson is not development; it’s fire. Last year, the Station Fire burned 250 square miles of the forest and communities near the observatory, and the tenacity of the firefighters was the only thing that saved Mount Wilson.

Sometimes historic observatories can’t be saved. Mount Stromlo Observatory in Australia, which has a telescope very similar to the one at the DDO, was overtaken by fire in January 2003, and all of their instrumentation was destroyed. The facilities at Mount Stromlo are being rebuilt, but the 74-inch telescope has been abandoned in place. Mount Stromlo is going to make its future by building instruments and controls for new cutting-edge telescopes like the Giant Magellan Telescope.

There’s another telescope similar to ours in South Africa. Their 74-inch telescope was built near the city of Pretoria in 1948, but after Pretoria grew, their telescope was actually disassembled and moved hundreds of miles across the country to a deserted location, away from light pollution. The move was finished in 1972. It’s really remarkable that a 74-inch telescope like that could be moved. I don’t think it could have been done after South Africa converted to the metric system. The new site has more recently been used for the South African Large Telescope, a giant dome with an 11-metre diameter mirror. Most of the interest in the site now is for the giant telescope, which is one of the two biggest ones in the world. The 74-inch telescope in South Africa is still used every clear night, according to Dr. Ian Glass, the telescope operator there.

The David Dunlap Observatory is close enough to Toronto that light pollution is a problem, but the Town of Richmond Hill’s anti-light-pollution by-law is one of the tools that minimize the impact of development. We have several observing methods that aren’t affected by light pollution, less than an hour’s drive away from 5 million potential astronomers in the Toronto area. We’d like to use the facility to inspire the next generation to wonder about the universe and our place in space and choose careers in science and technology. We have a wonderful new mission for the future that will keep the telescope an active and integral part of the community and Canadian science education.

And if you’re interested in an observatory or a planetarium in your town, go out and show your support. The organizations and universities that fund astronomy in your country are probably interested in funding the most sophisticated astronomical research, the kind that can only be done in space or on remote mountaintops… and who can blame them?! If those funding dollars are being spent on remote observatories in other parts of the world, it’s up to you to work with those funding authorities and landowners to keep operations going at your local astronomy center.

End of podcast:

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