The Dominion Observatory – 100thAnniversary

Randall Brooks (CSTM) and Calvin Klatt (NRCan)

The early astronomical work — 1905-1930s

     Following Canadian Confederation in 1867 government astronomy was primarily associated with surveyors who needed a means to determine the difference in longitude between their location and Greenwich. This required accurate tables of the positions of astronomical objects, precise and accurately calibrated theodolites and transit telescopes as well as access to chronometers.  Surveyors and a small number of astronomers were hired by the Geological Survey of Canada (founded 1841), the Hydrographic Survey (1880s), the Topographic Survey (1880s) and Geodetic Survey of Canada (1909). Among other duties, these astronomers/surveyors laid out the boundaries between the US and Canada and between provinces.      In Ottawa, the Cliff Street Observatory (near the current Supreme Court of Canada and overlooking the Ottawa River) was constructed in the 1880s to house transit telescopes to regulate precise clocks and to act as a primary reference point for surveyors. However, a key element was missing, an observatory to mirror in Canada the functions of the Royal Observatory at Greenwich. In 1898, one of the astronomers, Otto Klotz had a vision of a grander facility — a “national observatory”. The result was the founding of the Dominion Observatory with Frederick King, the Chief Astronomer, as its first Director. The Observatory’s principal functions were to be the primary longitude for Canada and to determine and distribute time to government departments, including Parliament, as well as to other businesses that required precise time, most notably the railroads. 

Image 1  Cliff Street Observatory.
Image 2  Klotz&King
    Construction of the building on which the 15” telescope’s dome was to be erected began in July 1902 when Klotz and King “laid out the line”, i.e. the orientation of building. To accommodate the transit instruments, the western portion of the structure is exactly on an east-west line.  On Aug. 12, 1902 the contractor, Theophile Viau, began excavation of the basement and 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 McGillvray&Labelle in 1904 with planned mid-April 1905 occupancy.    

The 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 as a notable landmark on the Central Experimental Farm in Ottawa. With a budget of $350,000 for the building and equipment, the telescope was ordered in June 1901 from Warner&Swasey of Cleveland with optics by John Brashear of Pittsburgh. The cost of the telescope was to be $14,625. It was completed in Jan. 1903. Precision sidereal and solar clocks, including one by Riefler, were ordered from Paris and received in Sept. 1902 at which point they began to be tested for accuracy and reliability.
Image 3    Construction
    The Dominion Observatory was completed in 1905 with “first light” with the main instrument, the 15 inch refracting telescope, occurring on 17th April. The Observatory became the primary reference point for anyone measuring time and geographical locations, latitudes and longitudes and altitudes in Canada. The new facility supported related functions but, most significantly for the astronomical community, added astrophysical studies to the daily responsibilities of the staff. Observatory staff were also given the responsibility of conducting seismic, magnetic and gravimetric studies related to underlying natural resources like iron and to the shape of the Earth.

Image 4  completed observatory
    The Canada Science and Technology Museum (CSTM) has some of the Observatory’s original transit telescopes but the largest, the so-called meridian circle transit, was apparently destroyed when the Observatory closed in 1970. Despite some early flaws that had to be resolved, it was the primary instrument to measure meridian transits of stars until the early 1930s when one of the older transit instruments was modified to improve its precision. The transit times were compared to measurements made at Greenwich, Washington and elsewhere to define Canadian time. 

The sidereal time was maintained on an electrically activated self-winding clock made by S. Riefler (CSTM’s Riefler clock was purchased at the same time but was sent to the Observatory in Saint John, NB) and the time signals were distributed via telegraph wires around Ottawa, to the railroads and to other government observatories in Saint John to Victoria.

The 15” refracting telescope installed in 1905 is the largest refractor ever erected in Canada. The original Brashear achromatic objective lens was replaced in 1958 with one that is better colour corrected for photography. The new lens, a triple apochromat made by Perkin-Elmer Corp., is the largest such lens ever made. The speed of the mechanical clock-work drive powered by falling weights was controlled by a fly-weight governor of the type invented by James Watt in the 18th century and often seen on steam engines. The telescope’s drive train was also replaced in the 1950s with a synchronous electrical motor.

Klotz’s interest in the Sun was accommodated by the purchase of a coelostat specifically designed to track and photograph the Sun and it’s spectrum. The instrument was, however, first taken to Labrador for a total solar eclipse in 1905. The months of planning and efforts by the more than a dozen astronomers in the expedition was thwarted by cloudy conditions. Back in Ottawa, a specially designed shed with roll off section housed the coelostat for almost 70 years. 
Image 5  Riefler clock
  
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 (e.g. the mirror transit and later the reflecting telescope of the Ottawa River Solar Observatory) and at radio frequencies (Algonquin Radio Obs. solar interferometer), until 1993 when the last of the solar programmes run out of NRC in Ottawa were wrapped up.    

Image 6  coelostat in Labrador, 1905
    One research programme at the new Observatory was to measure the motion of visual binaries and multiple star systems. Warner&Swasey built a filar micrometer for this work but the astronomers soon became much more interested in the astrophysics of the stars and nebulae. The acquisition of additional instruments supported the new research efforts. The early spectrograph used several glass prisms although the coelostat used gratings including one made at Mt. Wilson on Rowland’s engine. Cameras on the spectrographs recorded spectra for later investigation. These spectra were visually measured on linear measuring engines including ones made by the German firms of Toepfer and Zeiss. 

Image 7  images -- filar micrometer, measuring engines
    Another major instrument was added in 1915 when the double astrograph designed and made by John Brashear was mounted in its own small dome adjacent to the main building.  One of the telescopes on the double astrograph incorporated an objective prism spectrograph with a thin wedge shaped prism mounted in front of the objective. This feature of the astrograph required that the guide telescope be adjustable in the direction it was pointed. Brashear’s novel arrangement compensated for the fact that the telescope with the prism viewed a field of stars off-axis from the direction the astrograph was pointed and the guide telescope’s mounting also allowed for scanning to find a suitable guide star. With the direct photos and objective prism spectra, the DO astronomers were able to discover cluster variable stars and to use the information to establish the distances to clusters of stars and associated nebulae.  

     Two early photometers from the Observatory’s equipment survive, one by Brashear and a later one (ca. 1930) by Kipp&Zonen. These were used to measure the brightness of stars either directly or later from the photos taken with the astrograph. Brashear’s was a wedge photometer meaning that it incorporated a neutral density optical wedge. The observer physically adjusted the position of the eyepiece mounted behind the wedge until the star just disappeared. The position of the eyepiece was mechanically marked on a chart so that the brightness each star could later be compared to others in the observing sequence. The Kipp&Zonen instrument incorporated a photosensitive cell but its sensitivity limited measurements to stars of magnitude apx. 7 to 7.5. In this day of CCD photometry, it is difficult to imagine the tediousness of the measurements and analysis that required attention to a variety of effects and possible errors, both systematic and non-predictable, in the photos and instruments.

Image 8  photometers

    Some of the more noteworthy events at the observatory were the apparent discovery of “Planet X” in 1928 by François Henroteau and Mim Burland, the determination of the solar rotation as a function of latitude by Ralph DeLury (both in the 1930s) and the discoveries of meteor impact craters mainly in the Canadian Shield (in the 1940s - 1960s) by C.S. Beals, Peter Millman, Ian Halliday and others. The Planet X photos have been lost, save a couple from a newspaper, and we can only surmise that the cause was plate flaws, though research by Paul Feldman may soon shed some new light on this embarassing episode in the Observatory’s history.  As an interesting aside, Mim Burland became the first woman in the Canadian government service to wear pants on the job — a necessity while observing long hours in Ottawa’s chilly winters. However, it took a ministerial waiver to do so!

     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 recognized the limitations of the 15” telescope and wanted a very much larger instrument. Using his political connections, he persuaded the Canadian government to fund a new observatory, the Dominion Astrophysical Observatory. When completed in 1917, the 72” reflecting telescope was the largest in the world but remained so for only a few months. World War I had delayed the telescope’s completion as the 72"mirror was to be cast in Belgium not far from the centre of the conflict.  Under Plaskett’s leadership — much to Frederick King’s chagrin — and with a large, well equipped instrument and a growing staff, Victoria became a leading centre for astrophysical studies.

Geophysical Operations

      As mentioned earlier, the Dominion Observatory had another mandate — the study of the planet Earth. In particular the Dominion Observatory led the way in Geomagnetism, Seismology and Earthquake Research as well as Gravimetry.

      Magnetic observations had been conducted prior to 1905 under the auspices of the Department of the Interior, and in 1907 “the observatory began systematic observations for terrestrial magnetism” (Report of the Chief Astronomer, 1908). The Dominion Observatory focused on repeat observations to monitor secular variation of the magnetic field, used to study processes in the Earth’s core.

      This effort continues today at the same location in Ottawa in the work of Natural Resources Canada, primarily through operations of magnetic observatories which record rapid variations of the magnetic field used in the study of the Earth’s ionosphere and magnetosphere as well as Earth-Sun interactions. Airborne geomagnetic data collection is used today for exploration and scientific purposes.

      Seismic operations began in the Dominion Observatory basement in 1906, and in April of that year produced a spectacular recording of the San Francisco earthquake. Otto Klotz was the Observatory’s first seismologist and by 1920 had established a national network of seismometers in Victoria, Saskatoon, Saint Boniface, Ottawa, Toronto and Halifax.

      These seismographs were in place to record the sequence of strong earthquakes in 1929 (magnitude 7, Grand Banks), 1933 (7, Baffin Bay), 1935 (6, Temiskaming) and 1944 (5.7, Cornwall). The Grand Banks earthquake caused a tsunami which killed 27 people. It took 40 years for another magnitude 5 or greater earthquake to occur in Canada (1982, 5.7, Miramichi).

         This seismic work led to an effort to quantize earthquake hazards. The first edition of the National Building Code of Canada (1941) included seismic provisions. The 2005 National Building Code follows this precedent with much more precise seismic hazards estimations.

         Geophysical understanding of earthquake processes has advanced significantly over the past century. Today the Dominion Observatory tradition is carried out through the Natural Resources Canada Natural Hazards program. A recent highlight is the discovery of “episodic tremor and slip” in the Cascadia subduction zone near Vancouver Island enabled by extremely precise GPS measurements combined with seismic recordings. These crustal motions (2-5 mm) gradually move up the length of Vancouver Island over about 15 days with surprising regularity (14.5 +/- 0.2 months) and are accompanied by a (previously inexplicable) “noise” on seismographs in the region. The direction of slip is opposite to the long term deformation motion.                            

         Gravity observations began slightly before the Observatory was built, in 1902, when a Mendenhall type pendulum gravimeter was acquired (manufactured by Fauth&Co., Washington, DC).  

The beautiful and superbly made pendulums used with this apparatus were, with meticulous care, used until the 1970s with more modern apparatus. The Askania torsion balance (ca. 1925‑1928) was designed to record observations photographically, as well as permitting visual observations. Gravity surveys were carried out, among other reasons, to locate bodies of ore that might be the basis of Canada’s growing mining industry.

Image 9  Mendenhall&torsion balance
        Later, precise spring gravimeters were developed, eliminating the use of pendulums. With improved instrumentation gravimeters were developed to withstand the rigours (and non-gravitational accelerations) of ship-borne or airborne data collection. Airborne gravity has been used in recent years in commercial exploration to discover diamond-bearing kimberlites in Canada’s arctic.

         “Absolute” gravimeters are now the tool of choice for precise in situ measurements. These gravimeters precisely measure the acceleration of a falling corner cube reflector in a vacuum."

The former Dominion Observatory gravity program is now carried out at Natural Resources Canada. A national gravity database with approximately 700,000 points collected over 50 years is used to provide a national picture for use in exploration. The primary use of this database today is the modeling of the Canadian geoid - an equipotential surface that corresponds to mean sea level. Absolute gravity is used to monitor vertical crustal motion and to establish a gravity reference system for commercial and scientific users of Gravity instrumentation.

Conclusion

        The Dominion Observatory is well known to older Canadians. It was the source of the daily time signal broadcast on CBC Radio from the 1930s until the time functions were transferred to the National Research Council in 1970. The advent and success of the National Research Council scientists in building an atomic clock precise enough to replace astronomical observations meant the Dominion Observatory’s days were numbered. The DO’s automatic talking clocks, continued to sound out the time every minute, day and night, until the Observatory’s closure in 1970. Following the closure, the astronomical functions of the Observatory, along with the time service, were transferred to the National Research Council while the geophysics functions were transferred to Natural Resources Canada.        

Following the Observatory’s closure, the 15” telescope was only used for public observing. However, by 1974 it became obvious that this function would be better served from the Canada Science and Technology Museum and it was moved to a new observatory at the Museum. The 15” continues to provide young people and old with memorable views of the night skies. In 1988 the observatory was named to honour one of Canada’s leading astronomers and an strong advocate of public education in astronomy and science, Dr. Helen Sawyer Hogg.

To commemorate the 100thanniversary of the Dominion Observatory, the Canada Science&Technology Museum will be opening a small exhibition on the 16th April. This is part of the Museum’s International Year of Physics exhibitionMégaSciencewhich includes a section on the Sudbury Neutrino Observatory, Nobel Awards and soon to include the ZEEP reactor (first reactor outside the US) from AECL and the Tokamak de Varrennes.

       As all CASCA members know, and is supported by paper citations, astronomy in Canada has been one of our strongest scientific disciplines. This status in astrophysical research is traceable to the founding of the Dominion Observatory and the vision of its early astronomers, Klotz, King and Plaskett. That path was set with the opening of the Dominion Observatory 100 years ago in April 1905 — a remarkable legacy for what was, at the time, largely a colonial scientific backwater. One wonders what those three astronomers would think of Canadian astronomical achievements of the last 25 years, the LRP and future plans for Canadian astronomy.
Image 10 15"Today
  

link to:http://www.sciencetech.technomuses.ca/english/whatson/hogg_observatory.cfm

Further Reading:

  • Peter William Basham and Larry Newitt, "A historical summary of Geological Survey of Canada studies of earthquake seismology and geomagnetism”,1993 Canadian Journal of Earth Sciences 30(2):372-390.
  • John Hodgson,The History of the Dominion Observatories: I 1905 - 1946; II 1946 - the present, Ottawa, 1965.
  • Photos: historic images: Canada Science and Technology Museum Archival Collections; others CSTM.