ObservatorySince the earliest civilizations, princes and priests have maintained observatories where, by observing the sun, moon, stars and planets, astronomers could determine the passage of the months, seasons and years and watch the skies for any changes, which they often interpreted as portents. Remains of these early observatories are found worldwide, Stonehenge being one well-known example. Early observatories were located to take advantage of their surroundings, ie, in open terrain with natural or artificial markers, and modern observatories continue to be located at carefully selected sites.
Of the observatories in use before the invention of the telescope, perhaps the most scientifically productive was that of Tycho Brahe, built 400 years ago on the island of Hveen in the Baltic Sea. Johannes Kepler used Tycho's precise sightings of the planets to establish his laws of planetary motion. The first telescopic observatory was that of Galileo (1609). The telescope consisted of tiny lenses mounted in wooden tubes. The era of big-telescope observatories began just over 200 years ago with Sir William Herschel and his metal mirrors in England. The 20th century has seen a constant growth in telescope size, number, complexity and performance.
Optical observations are made by means of light, ie, those "optical" photons to which our eyes are sensitive. A star emits photons in great variety and abundance and in all directions. A tiny fraction of them arrives at Earth. Modern optical telescopes employ concave mirrors as the primary means of collecting photons. An image of the star or other celestial body is formed at the focus of the mirror. At that point the image can be recorded photographically or, more efficiently, by one of a variety of modern photon detectors; in fact, charge-coupled devices (CCDs) are now the detectors of choice.The aim is to extract the maximum information from the photons about the nature, behaviour and environment of the distant object they came from. The larger and more nearly perfect the mirror, the more information it collects at one time. Knowledge can be greatly increased if the individual regions of the spectrum of the object, rather than simply its direct image, can be recorded.
Successful observations depend on many factors, one of which is the siting of the observatory. The best locations will have relatively few cloudy periods throughout the year, air as transparent as possible (mountain tops are preferred) and freedom from local air turbulence and higher-altitude temperature fluctuations. The latter factors can blur the image or cause it to be unsteady. Stable electric power, staff living quarters and technical support facilities must be provided. The major observatories are so remote and of such complexity that they need to be generously supported, usually at the national or international level. Astronomers from distant places, after their proposed programs have been carefully screened, take turns for short periods as users.
Radio ObservatorySoon after the discovery of radio waves by Heinrich Hertz in 1887 came the realization that objects that emit light and heat also emit radio waves. Thomas Edison appears to have been the first to suggest the possibility of detecting radio waves from the sun, and several early attempts were made to do this. However, extraterrestial radio signals were not discovered until 1932. During an investigation of the origin of radio interference (static), Karl Jansky, an American engineer, noticed that his antenna was receiving radio noise from the direction of the centre of our GALAXY.
Grote Reber built the first equipment specially designed to study long-wave radiation from celestial bodies. The first radio astronomical observations in Canada were made in 1946 by A.E. COVINGTON, working at the NRC in Ottawa. When RADAR research was curtailed at the close of WWII, Covington used surplus equipment to construct a radio telescope which he used to detect radio emissions from the sun. The NRC has continued the program of radio observations of the sun to the present day.
Both optical and radio telescopes collect energy in the form of electromagnetic radiation. They differ, however, in the frequency (wavelength) of the radiation that they can detect. Radio waves that can penetrate Earth's atmosphere have wavelengths ranging from a few millimetres to tens of metres (about 10 000 to 100 million times longer than light waves). Telescopes for observations at shorter radio wavelengths often resemble optical telescopes and normally consist of a parabolic dish, analogous to the mirror of a reflecting telescope. Telescopes for use at long wavelengths are quite different, usually consisting of large arrays of individual radio antennae.
Radio signals reaching Earth from celestial sources are exceedingly weak; therefore, radio telescopes must have large collecting areas. A more important consideration is often the telescope's resolving power, ie, its ability to reveal detail in an object's radio image. The resolving power of a telescope is directly proportional to its linear dimensions (not its collecting area) and inversely proportional to the operating wavelength. Since radio wavelengths are long, radio telescopes must have large dimensions to possess even modest resolving powers.
For example, the human eye can just distinguish 2 points with an angular separation of one minute of arc. To do the same thing, a radio telescope operating at a wavelength of one metre must have a diameter of about 3 km. Since it is impractical to build single structures of such dimensions, radio scientists have devised ways of interconnecting several smaller elements (dishes or antennae) to produce a single telescope. Both single- and multi-element telescopes are used at Canadian radio observatories.
The NRC's Herzberg Institute of Astrophysics operates 2 national radio observatories: the Algonquin Radio Observatory (ARO) and Dominion Radio Astrophysical Observatory (DRAO). Both sites were chosen for their freedom from man-made radio interference which can readily spoil measurement of the very weak signals from astronomical sources.
ARO, located in the central region of Ontario's ALGONQUIN PROVINCIAL PARK, began operation in 1960 with the transfer from Ottawa of the solar program, which was becoming increasingly affected by radar and radio interference. A parabolic telescope was installed to monitor solar emission continually at a wavelength of 10.7 cm. To extend the time during which the sun is under continuous observation, an identical telescope was later installed at DRAO.
The dish is relatively small (1.8 m diameter), since its purpose is to collect radiation from the sun's entire disc. The intensity of the radiation at a wavelength of 10.7 cm is an effective measure of the general level of solar activity, and a sudden enhancement indicates the occurrence of a solar flare. The measurements are important in studies of the relationship between solar activity and geophysical phenomena (eg, NORTHERN LIGHTS). Determination of the position of localized regions of intense solar emissions is made at noon each day, using a multi-element telescope that produces strip scans of the sun with a resolution of 1.5 minutes of arc (ie, one-twentieth of the sun's diameter) in the east-west direction. When compared with optical photographs, these scans enable the regions of enhanced emission to be identified.
Another telescope located at the ARO is a large parabolic dish (46 m in diameter) completed in 1966. This instrument has been used by many observers on a variety of programs, including studies of PLANETS, interstellar matter, external galaxies and QUASARS. These observations are limited by the accuracy of the parabolic surface to wavelengths longer than about 1 cm.
It had been planned to replace the original surface with a more accurate one which would permit observations to be made at wavelengths as short as 3 mm. However, in 1987 the NRC decided not to proceed with the resurfacing but opted instead to close down operation of the 46 m telescope and acquire a 25% share of the James Clerk Maxwell Telescope (JCMT), located near the summit of Mauna Kea in Hawaii and operated from the Joint Astronomy Centre in Hilo, Hawaii. It seeks naturally emitted microwaves and is capable of exploring radio waves with a range of about .3 to 2 mm. It was built jointly by the UK and the Netherlands and is funded by them and by Canada.
DRAO, situated in a secluded valley south of Penticton, BC, opened in 1960. The first instrument, a 26 m parabolic telescope and associated receiver, was designed primarily for studies of our galaxy, a field in which Canadian optical astronomers have made significant contributions. The dish's surface is aluminum mesh, an almost perfect reflector at a wavelength of 21 cm, which is the wavelength of emission and absorption of hydrogen gas, the major constitutent of interstellar space. From observations of the distribution of this gas in the galaxy and its motions, as revealed by shifts in the observed wavelength, much has been learned about our galaxy's structure and dynamics.
The telescope accepts radiation from an area of the sky about 0.5° in diameter, but the much smaller angular structures of many nebulae and other objects in our galaxy cannot be revealed by the telescope. In addition, the resolving power is inadequate for studies of even the closest external galaxies. Since construction of a parabolic telescope of sufficient size is impractical, a different instrument has been constructed, the Aperture Synthesis Telescope, which uses a technique first developed at Cambridge University. The telescope consists of several 8.5 m parabolic dishes, the outputs of which are combined. Two of the dishes are movable on an east-west track 300 m long; 2 are fixed, one 300 m east of the track and the other 300 m west.
The 4 dishes observe the same region of the sky for 12 hours at each of about 120 positions of the movable dishes. When used with its spectrometer receiver, the system produces computer maps at 128 wavelengths of an area of the sky 2° in diameter, with a resolution of one minute of arc. The performance of this telescope is soon to be improved by increasing the number of dishes from 4 to 7.
For observations at a wavelength of 13.5 m, the observatory uses a telescope consisting of a large number of collecting elements or dipole antennae, laid out in a horizontal plane in the form of a "T." Each dipole is connected by cable to the centre of the array, where the signals are amplified and recorded. The crossbar of the "T" is 1.3 km long and the entire array occupies an area of 65 000 km2. Its performance is approximately equivalent to that of a conventional paraboloid 750 m in diameter.
In 1967 radio astronomers and engineers from Canadian universities and the NRC pioneered the development of a powerful new technique which has dramatically increased the resolution attainable at radio wavelengths. Known as Very Long Baseline Interferometry, the technique allows signals collected with widely separated telescopes to be combined to form a single instrument. Independent, highly stable atomic clocks are used to convert the signals collected at each telescope to lower frequencies which can be recorded on magnetic tape, together with accurate time markers. The tapes are subsequently brought together and played in unison.
For the initial experiments, the parabolic telescopes at Penticton and Algonquin Park were used to form a 2-element interferometer. More recently, however, a number of the world's radio telescopes have been used simultaneously to form a powerful, integrated instrument capable of producing images that reveal detail of the order of one-thousandth of one second of arc. This is 100-1000 times better than can normally be obtained with the largest optical telescopes. Thus, it is now possible to study the structure of quasars and the small cores of galaxies, to observe changes in their structure with time and to investigate details of many other radio sources.
In addition, very accurate determinations of the positions of radio sources are now possible, permitting the investigation of relativistic and other effects. In geophysics the ability to measure small angular displacements can be inverted to study the motion of Earth's axis of rotation, variations in its rate of rotation and movements of its crust, etc. These and other possibilities have led to an imaginative proposal by Canadian scientists to build a Canadian Long Baseline Array consisting of 8 radio telescopes in a line from BC to Newfoundland, operating as a single instrument. If constructed, it would be the world's largest telescope, as large as Canada itself. However, approval for this major undertaking has not been obtained.
Various kinds of electromagnetic radiation (ie, very low-energy infrared radiation and high-energy ultraviolet and X-ray radiation) are incapable of penetrating Earth's atmosphere and must be observed from the upper atmosphere or from space. Upper-atmosphere observations have been an ongoing part of Canada's satellite-research program since its inception, and the NRC is involved in various space-oriented programs with the US and European space authorities (NASA and ESA, respectively). The most dramatic of these projects is Starlab, a joint Australia-US program to construct a 1 m uv telescope equipped with a camera and spectrograph, to be carried to one of NASA's proposed space platforms aboard a Space Shuttle flight in the late 1980s. The Canadian government withdrew from the program in 1984. NASA launched the telescope in 1985. It was the second Skylab mission, the first having been in May 1973. The space station fell out of orbit on 11 July 1979, burning up on re-entry, with some of the debris scattering over the Indian Ocean and Australia.
DONALD A. MACRAE
Authors contributing to this article:
Early ObservatoriesThe earliest observatory in North America was likely that at LOUISBOURG (1750-51). A number of observatories with modest telescopes were created in Canada in the 19th century: Fredericton, 1851; Québec City, 1854; Kingston, Ontario, 1856; and Montréal, 1879. An early observatory at Toronto, under government auspices, was devoted to observations of geomagnetism and, later, METEOROLOGY as well as ASTRONOMY. In those days, much effort was expended in the determination of longitude by astronomical observations, and indeed it was the opening up of the Canadian West and the need for accurate surveys and maps that led to the founding of the Dominion Observatory in Ottawa in 1905. Although its primary purpose was geodetic and included the provision and distribution of precise TIME signals, research in "physical astronomy" was not neglected. Physical astronomy, now called ASTROPHYSICS, was to develop rapidly.
Dominion Astrophysical Observatory
Within 8 years the federal government decided to build an astrophysical observatory to be furnished with a telescope which, in its time, was the largest in the world. After a careful survey, Victoria, BC, was selected as the best site in Canada, with a large percentage of clear nights and "good seeing" (steady and pointlike star images). The Dominion Astrophysical Observatory (DAO) began its work in 1918, specializing in observing the spectra of faint stars and measuring their velocities by means of the Doppler effect. Operated now by the Herzberg Institute of Astrophysics, a component of the NATIONAL RESEARCH COUNCIL OF CANADA, the DAO has 2 large telescopes, the original (1.83 m) and a newer but smaller one (1.22 m). The original, recently named the Plaskett Telescope, has been completely modernized. It is used nearly equally in the imaging mode for the study of star clusters, nearby galaxies and stars of special interest (seeSPECTROSCOPY). The smaller one, dating from 1962 but also modern in every respect, is dedicated to the study of stellar spectra.
Although one speaks of "optical" observatories, modern technology allows the range of the observable spectrum to be greatly extended, not only shortward to ultraviolet rays but also longward into the invisible and previously little-explored infrared. A strong instrument group at DAO has been very active in working towards this goal and in improving the performance of spectroscopic instruments in general.
The Canadian Astronomy Data Centre (CADC) was established at DAO in 1986, to be one of three worldwide archive and distribution centres for data from the Hubble Space Telescope. The archived data from the Canada-France-Hawaii Telescope are also located there. CADC has developed software tools for accessing these and other computer-based data archives via the INTERNET.
David Dunlap Observatory
A generous gift from the DUNLAP family enabled University of Toronto in 1935 to establish the David Dunlap Observatory (DDO) in Richmond Hill just outside Toronto. It was equipped with a 1.88 m telescope, then and still the largest in Canada. Kept up-to-date instrumentally, it is nowadays used exclusively for stellar spectroscopy (revealing the physical conditions and the atomic/molecular constituents of the surface layers of a star).Two newer and smaller telescopes are currently dedicated to studies of properties of variable stars. Much of the work carried out at DDO supports the research of graduate students at U of T.
University of Toronto Southern Observatory
In the 1960s, due to increased enrolment in graduate studies, it became necessary for the U of T to seek additional dependable observatory facilities, DDO's research expanded into southern skies, where the richest regions of the Milky Way and its 2 satellite galaxies, the Magellanic Clouds, can be observed. In 1971 a 61 cm telescope was erected by the U of T on Las Campanas in Chile, a mountain on the west slope of the Andes, 29° south lat of the equator, in a region which encompasses some of the world's most highly prized observing sites.
Surprisingly, the U of T Southern Observatory's (UTSO) small telescope was for many years the most productive of all Canadian telescopes in terms of research output. In 1987 Manitoba-born Ian Shelton, then U of T's resident astronomer at Las Campanas, discovered Supernova 1987A (a disrupting star) in the nearby Large Magellanic Cloud; it became one of the very brightest and most intensively studied of supernovas. Astronomers from other institutions are frequently granted observing time. In 1992 the telescope was named in honour of one of Canada's foremost astronomers, Helen Sawyer HOGG-PRIESTLEY. A small telescope can be effective and is often preferred for certain types of observation. The Hogg telescope is used in both the imaging and the spectroscopic modes in a variety of programs.
Over the years the instruments provided by the DDO instrument group for the UTSO have been continuously updated, with corresponding improvements in its research potential. On-site computer facilities, vital to any observatory small or large, are in place. Computers are essential for the acquisition of most data. Often used for a quick look, the data is then transferred to tapes for transport home where detailed studies are carried out and then are permanently archived.
A more recent development for Canada in ground-based optical observatories has been the construction of the Canada-France-Hawaii Telescope (CFHT) atop Mauna Kea on the island of Hawaii. During the 1960s several groups in Canada pointed out the country's need for a larger and more up-to-date telescope.The federal government was sympathetic and finally decided on a joint undertaking with France and the state of Hawaii.The site, 20°N lat of the equator and at an altitude of 4250 m (above 40% of Earth's atmosphere), is regarded as the best in the Northern Hemisphere.
A 3.6 m telescope of modern design was inaugurated in September 1979. Its mirror surface was ground and polished by a team in the DAO optical shop, and the claim is made that the CFHT can deliver the best images of all ground-based telescopes. The CFHT is equipped with advanced instrumentation in great variety. Many are outgrowths of Canadian instruments developed at DAO. Canadian astronomers from observatories and universities all across the country compete for 45% of the CFHT telescope time; the rest is used by France and Hawaii.
The observational programs carried out at CFHT reflect the wide research interests of its multinational users. From the start the aim has been to exploit the unexcelled seeing (the ultrasharp star images) and the dark transparent skies above Mauna Kea. In the case of seeing, an imaginative instrument has even further improved the form of the images to the point where they begin to rival those of the Hubble Space Telescope in sharpness. With it, a few individual stars in a far-off galaxy have recently been separately distinguished, taking us a step closer to measuring the distance of that and other galaxies and ultimately to determining the age and size of the universe.
Very faint galaxies and star clusters are receiving much attention - their centres and faint peripheries are being probed more deeply than ever to map out their structures and motions and reveal the often unusual variety of their stellar populations. A recent detailed study of 6 nearby galaxies has led to the belief that super massive Black Holes (millions or billions of times the mass of our sun) exist at the very centres of those galaxies.
Another ingenious CFHT instrument makes it possible to record the spectra of as many as 100 very faint galaxies simultaneously - a 100-fold increase in efficiency - in order to measure their redshifts and increase our knowledge of the distant early universe. Closer to home, among stars that are neighbours of the Sun, several have been revealed by CFHT spectroscopy to be co-orbiting pairs, and a few of them are thought possibly to have planetary systems.
Canada is one of the major participants in the Gemini project, along with the US, Britain, Brazil, Argentina and Chile. As the name implies, the project will eventually see the completion of 2 observatories, in Hawaii and Chile. The northern telescope was dedicated in June 1999. The 8.1 m diameter telescope sits atop Mauna Kea, an extinct volcano on the island of Hawaii and the state's highest point.
The thickness of each Gemini mirror is only one-fortieth of its diameter. Therefore, because of its own weight, it will bend out of shape as the telescope is tilted to the sky. No matter, 120 computer-controlled hyrdraulic actuators behind it restore its precise shape ("active optics") and maintain it from minute to minute during the course of an observation, even if that is of several hours' duration. Beyond that, if and when atmospheric distortions spoil a star's image, a thin reflecting mirror in the convergent beam, located close to the focus and under computer control, changes in shape in such a way as to instantly cancel out the effects of the distortions. The design and fabrication of this innovative "adaptive optics" feature in the twin telescopes was one major Canadian responsibility.
The Gemini/Hawaii mirror has a silver reflecting surface, instead of the usual aluminum. Silver is a better reflector of infrared rays, while Mauna Kea is considered the best of all developed sites for making observations in the infrared. At that site and altitude the dry air above is very transparent to infrared rays, and the background sky is almost black. The telescope structure was engineered to give unique performance in the infrared. New infrared detectors are now available to exploit this part of the spectrum, which holds great promise for astronomy. Everything that might act to reduce a telescope's efficiency will be under direct control at all times. The design and construction of the telescope enclosures (the dome, its support and below-ground services) were done by Coast Steel Fabrications Ltd of Port Coquitlam, BC. The complex system for the control of the rotating part of the enclosures was developed by staff at DAO in Victoria.
A number of individual Canadian astronomers and groups worked with DAO in several areas of development for the telescopes, notably in the design of an adoptive optics system in the infrared for the Hawaii twin and multiobject spectrographs for both telescopes. The latter project was carried out in collaboration with a team of UK astronomers. CADC developed the system for handling and archiving data.
These two supertelescopes will have a major impact on astronomy and its allied sciences. Located one in each hemisphere, they will permit studies which can uniformly encompass the whole sphere of the sky. The size of their mirrors and their designed efficiencies will accelerate answers to key questions and allow precision probing for key objects to ever-greater distances. Canadian astronomers are eagerly looking forward to participating actively as observers with the Gemini telescopes. Astronomers viewing space through the Gemini telescope will be looking at light produced long ago, essentially looking back in time to the most distant galaxies. The second Gemini telescope, identical to the first, is under construction on Cerro Pachone, Chile, and will look at the southern skies. It is scheduled to open one year after the Mauna Kea telescope.
Canada, like other countries searching for a fuller understanding of the universe, has many smaller observatories from coast to coast. Major universities that maintain observatories for instruction and research include St Mary's U (at Halifax),U de Montréal and Laval (jointly on Mont Megantic, Qué), U of Western Ontario (near London), York U (at Toronto), U of Manitoba, U of Alberta, U of Calgary, UBC, U of Victoria and others. Several amateur astronomy centres across Canada have their own telescopes and permanent observatories.
DONALD A. MACRAE