July 28, 2010
On a 230-metre mountain just north of Victoria, the Dominion Astrophysical Observatory (DAO)’s 1.8 metre reflecting telescope has probed the night skies for 92 years. It’s apt now that Parks Canada should designate the observatory as a national historic site to recognize its importance to Canadian astronomy’s development.
“The DAO and its early staff helped bring Canadian astronomy to an extremely high level of international regard,” says its director, Dr. Jim Hesser. He adds that the Parks Canada designation allows NRC to maintain the Observatory as a working scientific instrument while respecting its historic architecture.
Warner and Swasey Co. of Cleveland, also a supplier to Ottawa’s Dominion Observatory, designed the Dominion Astrophysical Observatory’s larger rotating steel dome and installed it in 1917.
According to Dr. Hesser, the Observatory building’s design may still say “1918” to casual eyes, but nearly a century of accumulated upgrades make the telescope 10,000 times more sensitive than it was when new — and thus capable of contributing to 21st century astronomical research.
The 1.8 metre diameter Belgian-cast glass primary mirror that first caught starlight on May 6, 1918, was replaced in the mid-1970s with one that is unaffected by temperature changes. The original spectrograph — an instrument that breaks down a star’s light to determine its chemical composition — has been upgraded many times. Digital cameras and a new polarimeter developed by the NRC Herzberg Institute of Astrophysics (NRC-HIA) have taken advantage of emerging technologies. But the building, Observatory dome and nine-metre steel telescope frame remain original.
“It’s pretty remarkable that after all these years, we’re still using much of the same equipment,” says Dr. David Bohlender, the NRC-HIA research officer in charge of the telescope. “We have plans to continue to enhance its operation over the coming years and look forward to carrying on the reputation of the Observatory.”
Old-fashioned horsepower carted the high-tech reflecting telescope’s heavy equatorial mount up to its home on Little Saanich Mountain (now Observatory Hill).
Dr. Hesser adds that the telescope’s original tracking mechanism — a “very beautiful” gravity-driven brass clock drive — remained so accurate that it was only disconnected in the late 1980s, in favour of a new computer system that automates telescope guiding and improves the accuracy of its pointing.
While much of Canadian astronomy’s focus has shifted toward larger and newer facilities such as the Canada-France-Hawaii and Gemini telescopes, such upgrades keep the DAO “in the picture.” Dr. Bohlender says the Observatory’s main strengths include hosting long-term observing programs, providing long blocks of uninterrupted observing time, and training next-generation astronomers for their scientific careers.
An ongoing program at the Dominion Astrophysical Observatory charts the orbits of potentially dangerous asteroids that pass near the Earth.
Dr. John Stanley Plaskett, the DAO’s designer and first director, was a trained machinist who had been an instrument mechanic at the University of Toronto’s physics department.
He became an astronomer at the Dominion Observatory’s 0.32 metre telescope in Ottawa after gaining his doctorate. Dr. Plaskett’s belief in simple, strong design is one reason why the Observatory on Vancouver Island has held up well for so long. And it helped establish NRC-HIA’s worldwide reputation for developing scientific instruments for optical and infrared telescopes.
In fact, this reputation continues to this day, and NRC-HIA still relies on the DAO telescopes as test beds for new instrument designs.
DAO director Dr. Jim Hesser says the national historic site designation recognizes the scientific vision of Dr. Plaskett and the Observatory’s early staff, as well as the Observatory’s physical structure.
“We are very proud that this designation has been awarded to the Observatory, and we’re also proud that, more than 90 years later, the Plaskett telescope is still contributing,” says Dr. Hesser. “The telescope also plays an important role in bringing the wonders of astronomy to tens of thousands of school children who visit us every year.”
When new, the DAO was briefly the largest operating optical telescope in the world. One of its first discoveries arose from a decade-long program that used the then new technique of spectrographic photography to chart the “radial velocities” — the speeds at which they approach or recede from the Earth — of hundreds of stars. This led to groundbreaking discoveries about our home galaxy, the Milky Way — DAO research published under Dr. Plaskett in the 1930s was the definitive word on the Galaxy until radio astronomy came online in the 1950s.
“It led to an absolutely fundamental result in our understanding of the size and the mass of the Milky Way Galaxy,” says Dr. Hesser.
The Observatory’s early astronomers also used spectrographic analysis to identify the nature of what is now routinely called the interstellar medium — gas and dust in the vast spaces between the stars. A quarter-century later, astronomers realized the interstellar temperatures derived from these observations helped prove the universe’s Big Bang birth.
Another fundamental contribution was the 1922 discovery of the most massive binary star known until recently — astronomers now call it Plaskett’s Star.
An ongoing program charts the orbits of potentially dangerous asteroids that pass near the Earth. And today, astronomy graduate students from the University of Victoria are classifying recently discovered supernovae with time scheduled every few weeks.
Many of the DAO’s early discoveries are so fundamental they’re now common knowledge to grade-school science students, but early last century they were groundbreaking. Dr. Hesser says this underlines the fundamental nature of the Observatory’s work.
“It has served us extremely well and it’s still producing good science,” he says. “For very little expenditure from NRC-HIA, the two DAO telescopes still contribute.”
The Dominion Astrophysical Observatory’s first director, Dr. J.S. Plaskett, clearly had international-grade research in mind from the start. His designs for the DAO’s original observatory and telescope were so well-thought-out that seven later observatories were modelled on the same blueprints — the last one in the 1960s.
“He was involved in every aspect — engineering, design, commissioning and then laying out the groundbreaking observing program. He set very high standards for research,” Dr. Jim Hesser says. “He and the other staff helped inspire Canadians to pursue lofty goals in astrophysical research, and to compete on an international level. It’s both the building and the telescope as well as the heritage of the staff’s wisdom that I think are honoured by the national historic site designation. In the history of modern astronomy, Plaskett and his associates were giants.”
“Plaskett was an innovator,” adds Dr. David Bohlender. “He took advantage of the very best technology of the era in the designs of both the DAO’s telescope and its spectrograph, always with a view to making the equipment very robust.”
In 1962, a separate dome with a smaller, 1.2 metre telescope dedicated to spectroscopy was built on site. The DAO became part of the NRC Herzberg Institute of Astrophysics (NRC-HIA) in 1970.
The original 1.8 metre instrument, used for spectroscopy about three-quarters of the time and direct imaging for the rest, was named the Plaskett Telescope on its 75th anniversary in 1993.
