The Electromagnetic Spectrum: Window on the Universe

Astronomers rely on electromagnetic radiation detected by different types of telescopes to determine the location, composition, temperature, motions and magnetism of celestial objects. Electromagnetic radiation travels in the form of waves at the speed of light (299 792 km/sec) through space. Electromagnetic waves range from very low frequency radio waves through infrared radiation and visible light to ultraviolet radiation, x-rays and finally, high frequency gamma rays.Together, these waves form the electromagnetic spectrum. Electromagnetic waves are characterized by their frequency and wavelength which are inversely related:the greater the wave's frequency, the shorter the wavelength.

Telescopes: Essential Tools for Astronomers
Telescopes provide the means to collect and analyze electromagnetic radiation from distant realms of the universe. Different types of telescopes are used for distinct regions of the spectrum such as visible light, near infrared, microwaves, and radio waves.

Planets, stars, gaseous nebulae, and distant galaxies appear differently when "viewed" in each region of the spectrum. This is because various types of radiation are sensitive to differences in the temperature and chemistry of the objects. Even the fact that an object can be readily detected by a particular wavelength gives the astronomer important clues, such as whether it is hot or cold.

There are different categories of telescopes: optical telescopes collect visible light, but other telescopes, for example radio telescopes, can collect radiation invisible to the human eye. Since Galileo pioneered the use of the optical telescope in the 17th century, increasingly more powerful instruments have been developed, including the Hubble Space Telescope and the new Gemini Telescopes. In 1932, Jansky invented radio telescopes, which have developed into facilities like the James Clerk Maxwell Telescope.

Optical Telescopes: Reflecting and Refracting

A device such as a lens, mirror or antenna collects electromagnetic radiation from celestial objects and focuses it onto a detector. Optical telescopes use special versions of the charge-coupled devices found in video cameras, while radio telescopes use specialized receivers like those in radios or TV sets.

The term refraction refers to the bending of light. Refracting telescopes employ a series of lenses to collect visible light. Most telescopes in use today are reflecting because bigger telescopes can be built with mirrors than with lenses. Reflecting telescopes have a concave primary mirror, normally parabolic in shape and located at the lower end of the telescope. It reflects the light of celestial objects to a focus. The light is often intercepted by a smaller mirror that reflects it down through a hole in the primary mirror to an instrument, such as a camera or a spectrograph, for analysis.

Together, radio and optical telescopes help astronomers to build a more complete picture of a region of space.

Radio Telescopes: Collectors of Invisible Radiation

All objects in space emit radio waves, so a radio telescope can be used to detect them. A large curved metal dish, or antenna that resembles a parabolic satellite TV dish, collects the radio waves and reflects them to a focus point above the centre of the dish. Here, a sensitive receiver converts them into an electrical signal, which is interpreted by a computer. Radio telescopes "see" through clouds of dust that optical telescopes cannot penetrate.

There are two types of radio telescopes- single antenna or multiple antenna (interferometer). Images are created by scanning a single-antenna telescope across the sky, or by letting the rotation of the Earth move a group of telescopes pointed at the source of the radio wave emission. This scanning creates a sequence of signals, coming from different parts of the source. A computer processes these signals to create a representative image of a celestial body.

National Research Council Facilities

The National Research Council (NRC) provides telescopes for Canadian astronomers and their students to use for their research. The largest facilities are international ones, located on the best sites in the northern (4200-m high Mauna Kea, Hawaii) and southern (2700-m high Cerro Pachón, Chile) hemispheres, where more than 300 nights a year offer clear viewing. NRC also operates radio and optical telescopes in British Columbia. Visitors are welcome at the B.C. facilities. NRC's Herzberg Institute of Astrophysics designs and builds the sensitive instrumentation and writes software that enable the telescopes to detect signals from the furthest realms of the universe. Astronomers must compete for access to telescopes and may spend only a few nights (or shifts) a year observing on any one telescope. Most of their time is spent analyzing the data they obtain on those nights.

Gemini 8-m Telescopes
Gemini is an international partnership of the US, UK, Canada, Chile, Australia, Argentina and Brazil. An optical telescope in each hemisphere allows astronomers to study the entire sky. Gemini North is located on Mauna Kea in Hawaii and Gemini South on Cerro Pachón in the Chilean Andes. The telescopes are designed to give exquisitely sharp images. Canada is providing sensitive equipment that will help Gemini users make many exciting scientific discoveries.

Canada-France-Hawaii 3.6-m Telescope (CFHT)
An optical telescope, CFHT began operating in 1979 as a partnership between Canada, France and the University of Hawaii. CFHT pioneered techniques, including "adaptive optics", to remove the twinkle from stars caused by the continual motions of the Earth's atmosphere, thus making CFHT renowned for very sharp images.

For Canadian astronomers, CFHT has played critical roles in their studies of massive black holes in the centres of galaxies, the evolution of stars, and in demonstrating that the universe will expand forever.

Dominion Astrophysical Observatory (DAO) Telescopes
NRC operates two optical telescopes located on 230-m high Little Saanich Mountain, 17 km north of Victoria, B.C.

With continual upgrading, the 1.8-m Plaskett Telescope (1918) remains highly productive. It was used during its first two decades of its life to measure accurately the size and mass of the Milky Way galaxy. Today, among many programmes, it is used to determine orbits of asteroids that might strike the Earth.

The 1.2-m McKellar Telescope (1962) is used for precision analyses of the properties of stars and pioneered development of techniques to find planets around nearby stars.

The James Clerk Maxwell Telescope (JCMT)

This 15-m telescope on Mauna Kea is a partnership between the UK, Canada and the Netherlands.Since its opening in 1987, the JCMT radio telescope has probed the interstellar medium, star forming regions, and the earliest phases of galaxy evolution, by studying their microwave radiation.

JCMT astronomers detected complex molecules in Comet Hale-Bopp (1997) that had never before been seen in a comet.

Dominion Radio Astrophysical Observatory (DRAO) Telescopes
Located near Penticton, B.C., the DRAO operates a seven-antenna radio telescope that is mapping large parts of the plane of the Milky Way galaxy to study how the interstellar gas changes from stellar birth to stellar death.

A 26-m diameter radio telescope is used alone (for example, to study pulsars), or is often used in conjunction with the seven-antenna telescope to provide more complete maps of the Milky Way.

A small radio telescope maintains daily records (dating back to 1946) of radio radiation from the Sun. These data are used worldwide for studying solar-terrestrial relationships such as long term climate change or predicting disturbances of power and communications caused by storms on the Sun.