Foundations of Construction: Enormous optical telescope craned into Observatory dome

By Susanna McLeod

Special to Ontario Construction News

Away from glaring city lights, the doors of the dome slid open in the dark night. The twinkling stars and heart-stopping elements of the vast galaxy overhead captivated astronomers, astrophysicists, and scientists delving into research in Richmond Hill, Ontario. Adjusting the alignment of the telescope, viewers peered far into the depths of space. Requiring special construction techniques and scientific considerations, Canada’s largest optical telescope opened in 1935 at the David Dunlap Observatory.

Adding astronomy courses to University of Toronto’s curriculum in the early 1900s, Dr. Clarence Chant realized that while the school was prepared to advance the science, local observatory technology was deficient. (Dr. Chant was regarded as ‘the father of Canadian astronomy’.) Paying for a suitable parcel of land was a challenge. After attending a public lecture, lawyer and mining businessman David Dunlap was interested in funding the project. Dunlap died suddenly, but his widow Jessie Dunlap stepped in.

After several years of hunting, a 189-acre farm was found north of Toronto, with an orchard and a high rolling hill. “Jessie Dunlap exclaimed ‘this is the place,’ and authorized its purchase for $28,000,” according to C.H. Russell in the Journal of the Royal Astronomical Society of Canada, February 1999. The project was announced in 1930 and named David Dunlap Observatory.

Architectural firm Mathers & Haldenby designed a Beaux-Arts Administration Building. (Two generations operated the Toronto architecture company from 1921-1996.) Chant organized the construction of the Great Telescope Dome to house the colossal instrument.

The 18.59-metre diameter steel dome was constructed in England. “The structure took two years to complete and cost a total of $51,000,” said Russell. The eighty-ton dome was dismantled and shipped to Toronto. Arriving on July 31, 1933. It was reconstructed by Dominion Bridge Company on the 30-metre high hill, and covered in flat-seamed copper panels.

Grubb, Parsons & Co. of Newcastle upon Tyne, England, was contracted to manufacture a substantial telescope. At a width of 74 inches (1.89m), the telescope weighed 23 tons, plus another 2-½ tons for the 30-cm-thick glass mirror disk that was cast at Corning Glass Works in New York. Installed by a specialized crane, the telescope was cautiously lifted “through the dome’s fifteen-foot-wide slit (4.5m).”

The magnificent optical telescope was the largest in Canada and the second largest in the world. At that time, the world’s largest telescope was built in 1917 at the Mount Wilson Observatory in California.

In Richmond Hill, the observatory’s “steel frame structure consists of a massive dome atop a two-storey cylindrical base,” said Parks Canada’s National Historic Sites. Raised retractable shutters opened to allow the telescope clear viewing access to the sky; the Great Telescope Dome possesses “louvred window shutters, the pilasters, the metal catwalks, ladders, and stairs that envelope the exterior… and projecting entrance vestibule with double-leaved panelled door.” The transom was an eye-catching bright blue.

The Administration Building was completed that year as well, with a construction price of just over $109,000. Featuring three smaller domes, the building housed the less-powerful telescopes. The symmetrical façade was built in ashlar sandstone with a central entrance to the double-wide memorial hall. Decorative characteristics, along with “string courses, quoins,” and “arched and circular windows” added to the Beaux-Arts plan.

The building’s interior was designed with an “ornamental compass in the terrazzo floor, the memorial tablet, the travertine marble walls and stair treads,” noted Parks Canada. An academic hub, the Administration Building included offices, labs, lecture halls, plus a dark room and a machine shop. Two other buildings were nearby, the one-storey wood-framed Radio Shack, and the original brick farmhouse.

Along with trees and lawns, a touch of inspiring planetary design was added with the construction of “the elliptical island within the driveway with paving designed to evoke Kepler’s 2^nd Law of Planetary Motion.” A sundial graced the grounds closest to the Administration Building and the parking lot.

“The observatory was home to generations of astronomers at the University of Toronto, combining a mandate of teaching, research and public accessibility,” said Parks Canada. Groundbreaking discoveries were made at the Dunlap Observatory, including Thomas Bolton’s research into black holes, confirmed in 1971.

In 2008, the university sold the David Dunlap Observatory and acreage to Corsica Developments Inc. and in 2017 the City of Richmond Hill acquired 40 hectares of the observatory site and parkland. The next year, the Richmond Hill David Dunlap Observatory introduced exciting summer camps, and astronomy programs for the public with engaging lectures and evening stargazing experiences.

A 40-acre segment encompassing the four Observatory buildings was designated a Historic Site of Canada in 2019. Among many factors, the location is defined as “a fine and well-preserved example of early to mid-20^th century design in Canada which combines Modern and Neo-classical elements, and the elegant Beaux-Arts Administration Building.”

Brilliant architecture and the stars, such a beautiful combination.

© 2023 Susanna McLeod. McLeod is a Kingston-based freelance writer who specializes in Canadian History.