Dominion Astrophysical Observatory

The observatory was established under the leadership of John Stanley Plaskett, a Canadian astronomer who had previously worked at the Dominion Observatory in Ottawa. The 1.83-meter reflecting telescope, designed by Plaskett and built by the Warner & Swasey Company, was the largest in the world when it began operation in 1918. Its construction was funded by the Canadian government as part of a broader effort to advance national scientific research. The dome, designed to withstand the region's mild but wet climate, was one of the first large observatory domes to use a horseshoe mount, a design later adopted by the Hale Telescope at Palomar.¹

The DAO's early work focused on stellar radial velocities and spectroscopic binary stars. Plaskett and his colleagues used the 72-inch telescope to measure the orbits of many binary systems, including the massive star system Plaskett's Star, which was discovered at the observatory.² The observatory also contributed to the calibration of stellar luminosity scales and the study of interstellar matter. In the mid-20th century, the DAO became a center for the development of astronomical instrumentation, including photoelectric photometers and spectrographs. Its staff played a key role in the early planning of the Canada-France-Hawaii Telescope.

In 1962, the DAO became part of the National Research Council of Canada, and in 1975 it was designated a National Historic Site of Canada.³ The original telescope remains operational, now used primarily for public education and outreach, while research activities have shifted to other facilities. The observatory also hosts the Plaskett Fellowship, a prestigious postdoctoral position named after its founder. In 2017, the DAO was transferred to the Royal Astronomical Society of Canada, which continues to operate it as a heritage site and educational center.⁴

Beyond its famous telescope, the DAO has a rich history of lesser-known achievements. During World War II, the observatory contributed to the war effort by testing optical glass for military instruments. The site also houses a 1.2-meter telescope that was used for the Dominion Radio Astrophysical Observatory's early work. The observatory's library contains a rare collection of astronomical photographs and plates, some dating back to the early 20th century. Additionally, the DAO was one of the first observatories to use a computer-controlled telescope drive, a system developed in the 1960s.

Radial velocity

The component of a star's velocity along the line of sight, measured via Doppler shifts in its spectrum.

Spectroscopic binary

A binary star system whose orbital motion is detected through periodic Doppler shifts in its spectral lines.

Horseshoe mount

A telescope mount design where the polar axis is supported by a horseshoe-shaped bearing, allowing for large apertures.