| |
| ||||||||||||||||||||||||||||
Proactive disclosure Print version   | |  Earth Sciences Sector The Dominion Observatory: 100 Years of Geoscience
by Calvin Klatt This article was originally published in ELEMENTS (Canadian Geophysical Union newsletter), vol. 24, no. 1 (January), pp. 2-5, 2006. We acknowledge the kind permission of the CGU to reproduce this article here.
The centenary of the Dominion Observatory in Ottawa was celebrated in June 2005 during "Open Doors Ottawa", an event providing public access to architecturally important buildings. This was a fitting event to celebrate the observatory because of its role in promoting science to the public over the years. As the home of the national time service the observatory was mentioned daily on CBC radio for several decades (1939-1970). In addition, the telescope was open for public observations on Saturday nights from 1905 to 1974. Of the more than 600 visitors to the observatory during the weekend event, many still associate the observatory with the time service announcements and many recalled Saturday night visits to look through the "giant telescope" (15" refractor).
The Dominion Observatory was founded for very pragmatic reasons. The objective was to have a longitude reference (with associated time signal) for surveying in Canada: "To open up the West". Surveyors in the field would compare the time signal of the Dominion Observatory with their local time determined by astronomical observations - the difference corresponding to the longitude difference between Canada's prime meridian (Dominion Observatory) and their location. In 1898, Otto Klotz, an astronomer in the Department of the Interior (who had spent a great deal of time working with the International Boundary Commission, surveying the US/Canada border), had a vision of a grand facility - a "national observatory" to mirror in Canada the functions of the Royal Observatory at Greenwich, England. The observatory was to be the primary longitude reference point for Canada and it was to determine and distribute time to government departments and to businesses that required precise time, notably the railroads. The cost estimate first given to the Minister of the Interior in 1898 was just over $16,000 for building, astronomical dome, telescope and clocks. The chief architect of the Department of the Interior, David Ewart, was put in charge and he was told to design a building that suited a location near parliament. David Ewart is one of the more important architects in Canadian history. He was also responsible for the Victoria Memorial Museum Building (Museum of Nature, 1905), the Royal Canadian Mint building (1905-1912) and the Connaught building (1914), all in Ottawa. The site was changed from near Parliament to the current location on the Experimental Farm (off Carling Ave.) in Ottawa because of better astronomical seeing. This site was then on the edge of the city and is slightly elevated. The exterior was built of Nepean sandstone and the trim of Credit Valley sandstone. The interior is simple painted brick.
Construction of the building began in July 1902. For positional astronomy purposes the western portion of the structure is exactly on an east-west line. The transit house marking the prime meridian, attached on the west side of the main building, was built separately. The final cost of the main building, including furnishings, but not the transit house extension or instruments, was $93,800. The total cost of the building and instruments was over $300,000!
The 15" refracting telescope was ordered in 1901. Precision sidereal time and solar time clocks, were ordered from Paris and received in 1902 at which point they began to be tested for accuracy and reliability. The Dominion Observatory building was completed in 1905 with the main instrument, the refracting telescope, observing for the first time on April 17th. The telescope was open to the public every Saturday night, with almost 3000 names recorded in the "visitor's book" during the summer of 1905. Public viewing continued until the telescope was moved to the Canada Science and Technology Museum in 1974, where it is still in use. The stone and brick buildings were famous for how cold they were, but the observatory was even colder.
Imagine the astronomers coming to work in the winter evenings, under clear skies, in the unheated telescope
dome - working with very little physical activity on cold Ottawa winter nights. One astronomer from the 1920s,
Mim Burland, became famous for being the first woman in the Canadian government service to be allowed to
wear pants on the job. It wasn't easy though - she had to get a ministerial waiver to allow her to do so!
NRCan's "Office of Energy Efficiency" now occupies the observatory buildings - presumably their work
environment is inspirational.
Aside from the time service and surveying, the Dominion Observatory had another mandate - the study of the planet Earth. In particular the Dominion Observatory was the leading Canadian organization in Geomagnetism, Seismology, Earthquake Research and Gravimetry for several decades. Magnetic observations had begun before 1905, and in 1907 the observatory began systematic observations of terrestrial magnetism. The main purpose of the magnetic observations was for navigational purposes. Magnetic observations were a natural adjunct to land surveying: To measure magnetic declination you needed to determine azimuth, latitude and longitude by astronomical means. The Dominion Observatory quickly specialized in "repeat" observations, which would extend the usefulness of observations made by the Topographic Survey, which was the group that actually produced the magnetic declination charts. The Dominion Observatory took over production of the magnetic declination charts in the 1940s. This effort continues today, primarily through the operation of magnetic observatories that record rapid variations of the magnetic field used in the study of the Earth's ionosphere and magnetosphere as well as Earth- Sun interactions. This work is very important because of the effect of the magnetic field on hydro lines and similar infrastructure. Seismometers were installed in the Dominion Observatory basement in 1906, and in April of that year produced a spectacular recording of the great San Francisco earthquake. By 1920 a national network of seismometers had been established in Victoria, Saskatoon, Saint Boniface, Ottawa, Toronto and Halifax. These seismographs were in place to record an unusual sequence of strong earthquakes in Eastern Canada:
The Grand Banks earthquake caused a tsunami killing 27 people. This seismic work led to an effort to quantize earthquake hazards. An early edition of the National Building Code of Canada (1953) included the first seismic hazard map of Canada and seismic provisions. The 2005 National Building Code has much more precise seismic hazards estimations based on the latest work of Natural Resources Canada. Geophysical understanding of earthquake processes has advanced significantly over the past century. A recent highlight is the discovery of "episodic tremor and slip" in the Cascadia subduction zone under 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 and are accompanied by a (previously inexplicable) "noise" on seismographs in the region. The slip events occur with surprising regularity (every 14.5 ± 0.2 months) with a direction of slip opposite to the long-term deformation motion.
Gravity observations began in 1902, when a Mendenhall type pendulum gravimeter was acquired. The beautiful gold plated pendulum was used, with meticulous care, until the 1970s. Gravity surveys were carried out, among other reasons, to locate bodies of ore that might be the basis of Canada's growing mining industry. Later, precise spring gravimeters were developed, eliminating the use of pendulums. Eventually these gravimeters could be used aboard ships and aircraft. 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 measure the acceleration of a falling corner cube reflector in a vacuum. 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 geoid - a surface that corresponds to mean sea level. A geoid model will become the official surveying reference for heights above sea level across Canada in the future. The observatory remained responsible for Canada's official time service from 1905 until 1970 at which time the
responsibility was passed to the National Research Council (NRC). By the late 1930s crystal oscillators had
been developed which were an improvement on the pendulum clocks in the observatory's underground vaults.
Eventually they were found to be more precise than astronomical time keeping and they formally took over from
the astronomical method in 1951. Astronomical work continued at the observatory, focussed on measurements
of changes in the Earth's rotation and orientation in space. In 1958 the NRC Cs-I ("Cesium One") clock was
assembled and was immediately made the master clock for the Dominion Observatory and Canada. The NRC
is currently experimenting with a "Cesium Fountain" which will be much more accurate than the current atomic clocks.
Following the founding of the Dominion Observatory in 1905, it provided the prime meridian and time service for Canada, as well as being the home for a wide range of geophysical research activities. The astronomical functions of the observatory, along with the time service, were transferred to the National Research Council in 1970 while the surveying and geophysics activities are now part of Natural Resources Canada. The 15-inch refractor telescope was moved to the Canadian Museum of Science and Technology in 1974. Natural Resources Canada still occupies the buildings on the site, but the "Seismology" building is the only one currently occupied by geoscientists. The observatory rotunda has an original painting of the zodiac by Juan Geuer, who worked at the observatory for 27 years and painted the ceiling in 1962. Juan has exhibited his work in leading art galleries around the world and has a permanent installation in the National Gallery of Canada. While the observatory is no longer used to view the heavens, the beautiful architecture and artwork of the
observatory rotunda will remain an outstanding part of our Canadian heritage.
Hodgson, J.H; The Heavens above and the earth beneath: a history of the Dominion Observatories: volume I 1905 - 1946; 1989, Geological Survey of Canada Open File, Ottawa. Hodgson, J.H.; The Heavens above and the earth beneath: a history of the Dominion Observatories: volume II 1946 - 1970, 1994, Geological Survey of Canada Open File, Ottawa. Thomson, M. M.; The Beginning of the Long Dash: a history of timekeeping in Canada,
1978, University of Toronto Press, Toronto.
|
