Early observations conducted during the installation phase have already demonstrated the power of this new instrument: many previously unknown moons of Jupiter have been discovered, potentially hazardous asteroids that pass near to the Earth have been studied, and wide areas of the sky have been surveyed to prepare targets for a future space mission.

MegaPrime is a collaboration between several research institutes in France, and NRC's Herzberg Institute of Astrophysics (HIA) in Victoria, B.C. Several major industrial contractors participated in building the large optical and mechanical components of this device, which is mounted at the prime focus of the CFHT.

At the heart of MegaPrime is MegaCam, a unique camera built by the French Commissariat � l'Energie Atomique (CEA). This camera is an array of 40 charge-coupled detectors (CCDs), each of which has nine million individual pixels. In routine use, MegaCam produces an image containing 324 million pixels.

MegaPrime on the CFHT provides Canadian astronomers with a capability that newer and larger optical telescopes do not offer: the ability to observe large areas of sky, in this case, an area larger than that covered by four full moons.

The huge number of pixels means that the images are obtained at very high resolution, allowing astronomers to zoom in and separate individual stars in crowded star fields, and to see the detailed structure of faint, distant galaxies.

Taking advantage of the capabilities of MegaPrime, a large team of astronomers in Canada and France has initiated the CFHT Legacy Survey (LS).

Under this five-year program, an equal partnership between Canada and France, some 500 nights of telescope time will be dedicated to three major projects:

1. the study of the Kuiper Belt -- a mysterious reservoir of ancient, dim asteroids that encircle the sun beyond the orbit of Neptune),
2. a survey that will reveal the large-scale structure of the dark matter in the universe by observing its weak gravitational lens effect on distant galaxies, and
3. a program to detect and study distant supernovae, titanic stellar explosions that can reveal the effect of dark energy on the evolution of the universe.

The availability of MegaPrime opens a new era in astronomical wide-field imaging that will benefit the worldwide astronomical community. All images taken with MegaPrime will be archived at the Canadian Astronomy Data Centre (CADC), part of NRC's HIA.

Astronomers from around the world will be able to access and retrieve MegaPrime images using the internet services offered through the CADC.

HIA's Director General, Dr. Gregory G. Fahlman, notes that "MegaPrime is a groundbreaking instrument that finally realizes a long-standing goal of optical astronomers: to acquire digital images of large areas of sky that were previously obtainable only with inefficient photographic plates.

"The speed and accuracy of MegaPrime opens entirely new opportunities for astronomical research and offers the promise of exciting new discoveries. The CFHT LS is a scientific program of remarkable ambition, made possible by MegaPrime and the development of new observing procedures at the CFHT.

"Canadian astronomers have a world-leading tool to further their original research and an opportunity to have a major impact in resolving fundamental questions about the nature of the universe. Moreover, the carefully archived images will provide a lasting legacy for the entire world to exploit in the future."

Canada has contributed three components to MegaPrime.

1. Before being captured by the MegaCam CCD sensors, the stellar light must pass through the Wide Field Corrector (WFC). This device is needed to ensure that a good image of the whole field of view is projected onto the camera's sensors. With four lenses, 50 to 80 cm in diameter, mounted in a structure that is two metres long and has a mass of 660 kg, the WFC is an amazing feat of optical construction. The WFC was designed at the NRC's Herzberg Institute for Astrophysics (HIA) in Victoria, BC, Canada, and manufactured at the Sagem works in Saclay, France.

2. The camera must be able to move along the optical axis of the telescope, to ensure that the images remain in sharp focus throughout the course of the night. An automated system, the focus stage assembly (FSA), was designed to sense continually the sharpness of the images formed by the WFC and to make small adjustments in the camera position as needed. The FSA was designed and built at HIA in Victoria.

3. As the Earth rotates on its axis, the telescope is tracked to compensate precisely for the apparent motion of the sky with time. However, this tracking is rarely precise enough to keep stellar images exactly fixed on the camera for the long exposures needed to see the faintest objects in the sky. The Earth's atmosphere also causes the stellar images to dance about and this would blur the images if uncorrected. In MegaPrime, these problems are addressed by two small 'guiding cameras' or 'guiders'. These devices form images of stars just outside of the field of view on the main camera. Several images are produced every second. These are analyzed and the data used to guide the main telescope automatically, making small adjustments that keep the field of view absolutely steady. These guiders were designed and built at HIA.

Recognized globally for research and innovation, Canada's National Research Council (NRC) is a leader in the development of an innovative, knowledge-based economy for Canada through science and technology. NRC operates world-class research facilities as well as information, technology and innovation support networks from coast to coast.

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