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The Dominion Observatory—100th Anniversary

Founding and Construction of the Dominion Observatory

Frederick King, ca 1910
Klotz envisioned an observatory whose function in Canada mirrored that of the Royal Observatory at Greenwich, but with a supporting role for surveyors. The result was the founding of the Dominion Observatory with Dr Frederick King, the Chief Astronomer, as its first Director. The Observatory’s primary function was to mark the primary longitude for Canada and the determination and distribution of time to government departments, including Parliament, and to other businesses that required precise time, most notably the railways.

This series of images shows various phases of construction of the Observatory’s sandstone building and the equipment used to lift the large stones, and eventually the dome and telescope, into place. The building still stands today, a notable landmark on the Central Experimental Farm in Ottawa.

(Fig.07a) (Fig.07b) (Fig.07c)
These photographs of the Dominion Observatory construction were probably taken by J. S. Plaskett, who arrived in Ottawa from the University of Toronto in July 1903. Below (right), the dome is installed in 1904.

(Fig.07d) (Fig.07e)

With a budget of $350,000 for the building and equipment, the telescope was ordered in June 1901 from Warner & Swasey and was to have optics by John Brashear. Both firms were located in Pittsburgh, Pennsylvania. The cost of the telescope was to be $14,625 and it was completed in January 1903. Precision clocks, including one by Sigmund Riefler, and sidereal and solar clocks were ordered from Paris and received in September 1902 at which point they began to be tested for accuracy and reliability.

Construction of the building on which the telescope’s dome was to be erected began in July 1902 when Klotz and King “laid out the line”—the orientation of building. Because of the transit instruments, the main portion of the structure is on an east-west line. The transit telescope and meridian instrument had to be accurately positioned to observe in the north-south plane of the sky — the meridian. On 12 August the building contractor, Théophile Viau, began excavation of the basement. The total cost of the contract was $74,999. The contract for the transit house, which was attached on the west side of the main building, was awarded to McGillivray & Labelle in 1904, with occupancy planned for mid-April 1905.

The Dominion Observatory was completed in 1905. This photograph was probably taken by J. S. Plaskett.

The Dominion Observatory was completed in 1905 with “first light” with the main instrument, a 15-inch (38-cm) diameter refracting telescope, occurring in spring, on 17 April 1905. The Observatory became the primary reference point for anyone measuring time and geographical locations—latitudes and longitudes and altitudes—in Canada. The new facility combined functions from several other government departments but significantly added astronomical studies of natural phenomena of the Sun and stars. Observatory staff were also given the responsibility to study gravity variations, which are related to underlying natural resources like iron, and to the shape of the Earth.

J. S. Plaskett illustrates the observing position at the meridian transit instrument, ca 1913–1916.
  (Fig.9) Sigmund Riefler’s precision sidereal clock (CSTM 1966.0545). The pendulum was maintained in a slight vacuum and given a periodic pulse by an electromagnet. The most accurate type of clock available from 1891 to ca 1928, such clocks had a precision of 0.015 second per day.

The key responsibility in the early years was time determination. This required the use of a type of telescope called a transit telescope. Its motions were limited to the meridian—the north-south plane of the sky and running through the zenith, the point in the sky directly overhead. The Canada Science and Technology Museum has one of the original transit telescopes but the largest, the so-called meridian circle transit, from the early days, was destroyed when the Observatory closed in 1970. Only photographs of it remain. Until the early 1930s it was the primary instrument to measure the time at which stars passed across the meridian. These times were compared to measurements made at Greenwich, Washington, and elsewhere, to define Canadian time. The time was maintained on a sidereal self-winding clock made by Sigmund Riefler (the Museum’s Riefler clock, 1966.0545, was purchased at the same time but came from the observatory in Saint John, New Brunswick) and the time signals were distributed via telegraph wires around Ottawa, to the railways and to other government observatories from Saint John to Victoria.

The Observatory’s main telescope (CSTM 1974.0488), ca 1930–32, the Warner & Swasey / Brashear 15-inch (38-cm) refracting telescope was, and remains, Canada’s largest.
The telescope’s original 15-inch (38-cm) doublet lens (CSTM 1975.1087) was made by John Brashear but was replaced in 1958 by the world’s largest three-component lens system (apochromat), manufactured by Perkin-Elmer Corporation of Norwalk, Connecticut. The focal ratio of the telescope is f/15 in a tube length of 225 inches (5.7 metres).

The 15-inch (38-cm) refracting telescope (1974.0488) installed in 1905 is the largest of this type ever to be erected in Canada and it is still used regularly at the Museum’s Helen Sawyer Hogg Observatory. The original Brashear achromatic objective lens (1975.1087) was replaced in 1958 with one that is better suited to photography. The new lens, a triple apochromatic made by Perkin-Elmer, is the largest such lens ever made. The telescope’s drive motor, to track the stars, was also replaced at that time. The original mechanical drive (1974.0488), which was driven by falling weights (like those that drive a grandfather’s clock), was housed within the telescope base. The speed of the motor was controlled by a fly-weight governor, invented by James Watt in the eighteenth century, and often seen on steam engines.

(Fig.12a)   (Fig.12b)
The original mechanical drive was powered by gravity driven weights. This drive was replaced in the 1950s. The fly-weight governor (CSTM 1974.0488.7, right) survives.

Klotz’s interest in the Sun was accommodated by the purchase of a coelostat (1966.0402), a telescope designed to track the Sun. The coelostat allowed astronomers to study the Sun’s composition by studying its spectrum, and to study sunspots by taking frequent photographs of the Sun each clear day. The instrument was, however, first taken to Labrador (1974.0754) for a total solar eclipse in 1905.

(Fig.14a)   (Fig.14b)
The coelostat set up for the 1905 total solar eclipse in Labrador. The expedition was chronicled photographically (CSTM 1974.0754) by J. S. Plaskett.

Back in Ottawa, a specially designed shed with roll off sections housed the coelostat for almost seventy years. From 1905 the Dominion Observatory’s astronomers made notable contributions to the study of the Sun, an aspect of Canadian astronomy that continued with new instruments, both optical and radio, until 1993 when the last of the solar programs ended.

The exterior of the coelostat shed at the Observatory
The Sun-tracking mirrors of the coelostat (CSTM 1966.0402); note the louvred shed walls, to prevent heat buildup.

Filar micrometer made by Warner & Swasey (CSTM 1970.0212) to measure separations between double stars

A prism spectrograph attached to the 15-inch (38-cm) telescope, ca 1930, was used to photograph the spectra of stars for classification and for measurement of velocities of double stars.
One of the studies of stars at the Observatory measured the motion of one star around another in binary or multiple star systems. Warner & Swasey built a filar micrometer (1970.0212) for this work but the astronomers soon became much more interested in the physics, or astrophysics, of the stars and nebulae (gaseous clouds or galaxies). These studies of the composition of the Sun and stars require an instrument called a spectrograph. These early instruments used several glass prisms to break up and spread the light of the object. A camera on the spectrograph recorded the spectrum for later investigation. Depending on the brightness of the star or nebula, an exposure lasted a few minutes to hours. The clock drive of the telescope was critical, as it moved the telescope to compensate for the Earth’s daily rotation.

The spectrum of the Sun as first drawn by Joseph von Fraunhofer, ca 1815 (Astronomische Nachrichten, 1874)

Two aspects of the spectroscopic investigations were most significant. Stellar spectra show lines (a sort of cosmic bar code) that vary from star to star, and can vary over time within one star’s spectrum. The positions of these lines, compared to a set of standard, known lines, indicates the star’s composition, and whether it is moving towards or away from Earth through a process referred to as Doppler shifts. The very fine measurements of these spectral lines were taken with a measuring engine, and the Museum has three of the Dominion Observatory’s early engines. These were made by the German firms of Toepfer (1970.0214, 1970.0221) and Zeiss (1970.0222).

(Fig.19a)   (Fig.19b)
Two of the Observatory’s engines for measuring the spectral lines on the photographs of spectra (CSTM 1970.0214, left; CSTM 1970.0222, right)

The double astrograph (CSTM 1966.0401) has two main cameras plus a patrol camera. The camera with the cap lifted has the thin wedge-shaped prism in front. The smaller telescopes are for finding the objects to be photographed, and to track the objects during the long exposure times.
Another major instrument was added ten years later. The double astrograph (1966.0401, a telescope with two cameras) was mounted in its own small dome adjacent to the main building. It was intended to photograph clusters of stars and to allow astronomers to measure the brightness of the stars on the photographs with an instrument called a photometer. One of the astrograph cameras has a thin wedge-shaped glass prism in front of it. This allows simultaneous photographs of the cluster stars and their spectra. This extra feature of the astrograph required that one of the telescopes be adjustable in the direction it was pointed, compensating for the fact that the telescope with the prism viewed a field of stars off axis from the direction the astrograph was pointed. With the photographs and spectra astronomers were able to discover variable stars, and used the information to establish the distances to nebulae and to clusters of stars.

The Museum has two photometers, one by Warner & Swasey and a later one by Kipp & Zonen (1970.1516, 1970.0213). These were used to measure the brightness of stars from the photographs taken with the astrograph. Warner & Swasey’s was a wedge photometer. The long black strip seen in the photograph is a photographic “wedge,” which varies in density from end to end. The observer physically adjusted the position of the eyepiece until the star just disappeared. The position on the chart indicated the brightness of one star compared to others—a combination of stars of known and unknown brightnesses. The later photometer, the Kipp & Zonen, was a type that employed the photoelectric effect discovered by Einstein in 1905. A light was projected through the negative of a photograph of stars onto a photosensitive tube. An electric current was thus created, which was proportional to the amount of light it received, and this indicated the brightness of the stars being measured on the photograph, one by one. The analysis process requires meticulous attention to a variety of effects and possible errors.

(Fig.21a)   (Fig.21b)
The smaller of these two photometers (CSTM 1970.0516, left) was made ca 1903 by Warner & Swasey and used a glass wedge. The other (CSTM 1970.0213, right), by Kipp & Zonen, dates from the 1930s and used light and electrical signals to make measurements.

Over the first few years of the Observatory’s operations, its astronomers, John Plaskett in particular, soon had a vision to expand the Observatory’s scientific studies. Plaskett wanted a very much larger instrument and he persuaded the Canadian government to fund a new observatory with what was to be the world’s largest telescope. The Dominion Astrophysical Observatory was built in Victoria, British Columbia. When completed in 1917, the 72-inch (183-cm) reflecting telescope was the largest in the world but remained so for only a few months into 1918. The First World War had delayed its completion, as the 72-inch (183-cm) mirror was to have been made in Belgium, near the centre of the conflict. Under Plaskett’s leadership, Canada became a leading centre for astrophysical studies, a position it still holds.