This Week in History


First Light at the Dominion Astrophysical Observatory

For the week of Monday, May 2, 2016.

On May 6, 1918, a gathering of astronomers witnessed first light at the new Dominion Astrophysical Observatory (DAO) in Saanich, British Columbia. This marked the beginning of nearly a century of astronomical observation using the Plaskett Telescope, the largest government-owned reflecting telescope in Canada.

When the DAO was built, all materials were brought up the mountain by teams of horses
© Albertype Company/Library and Archives Canada/PA-032169

In 1912, astronomer John Stanley Plaskett convinced the federal government of the need for a new observatory to replace the inadequate 16-inch telescope at Dominion Observatory in Ottawa. Surveys were conducted across Canada for a new location and Saanich was selected for its stable atmosphere, low precipitation, and moderate temperatures.

Construction on the dome finished in 1916, but it took two more years before the observatory opened its shutters due to issues with the telescope’s primary mirror. The 1.83-metre mirror was cast in France and shipped just a week before the outbreak of the First World War. A test mirror meant for practising the finishing technique was never shipped. Without this blank, it took a further two years and three attempts to polish the more than 4,000 lb (1.814 metric ton) of glass to the proper curve.

Two views of the Plaskett Telescope. Updated over time, it still retains many of its original components
© Left: Floyd K. Darrow, “The Giant Canadian Reflector” Electrical Experimenter Magazine, Vol. 7, No. 10, February, 1920; Right: Parks Canada/Agence Parcs Canada, Andrew Waldron

The Plaskett Telescope would have been the largest in the world, but delays meant the title went to the Hooker Telescope at Mount Wilson Observatory, which had opened just six months earlier. Nonetheless, the DAO has contributed to many major discoveries, including determining the size and rotation of the Milky Way galaxy. Plaskett also used the telescope for his discovery of a large spectroscopic binary (two stars orbiting the same point), which helped him earn the Gold Medal of the Royal Astronomical Society in 1930. Perhaps the telescope’s most impressive use was its availability to the public. For 95 years, the DAO held observation open houses and educational programs.

John Stanley Plaskett, the first director of the DAO and namesake of the Plaskett Telescope, was designated as a National Historic Person in 1949. In honour of its legacy of astronomical discovery and its continued importance to astronomy, the Dominion Astrophysical Observatory became a National Historic Site in 2010.

June 6, 2016, will be the 100th anniversary of the National Research Council of Canada, where the Herzberg Institute of Astrophysics has been anchored by the Dominion Astrophysical Observatory since 1995. For more on astronomy in Canada, please read The Stars Reveal Their Secrets and Head in the Stars and Feet on the Ground in the This Week in History archives. For more about the National Research Council of Canada see An Educator Through and Through.

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