The MegaCam CCD mosaic

Various resolution downloads:
[Full scale - 954x805 - JPEG - 84Kb] 
[Scaled 1/2th - 476x402 - JPEG - 19Kb] 

Technical description:

Astronomical objects emit electromagnetic radiation in all spectral bands, from the shortest gamma rays, to X-rays, the ultra-violet, the optical, the infrared, and through to the millimeter and longer radio waves. In each band, specialized equipment is needed to detect the presence of this radiation. Before electronic detectors (and access to Space) allowed us to exploit the other bands, astronomical science developed using only knowledge obtained from optical observations. 

Fortunately, the stars, the main constituent of luminous matter, emit at visible wavelengths. As a consequence of the Earth's transparent atmosphere, a natural detector has evolved - the human eye - which allows us to see the sunlight, and as a consequence, all the other stars as well. While our picture was rather incomplete, the basic nature of the universe was deduced from optical observations using first the eye, then photography and more recently, various kinds of electronic detectors. 

The optical band is still a very productive field of research, because light detectors have made spectacular progress in the past decades. The CCD (Charge Coupled Device) reigns as the detector of choice for astronomers; it is used in 99% of all professional optical observations collected in the world today. However, the physical scale of today's semiconductors is driven by mass- market needs, especially for computer processors. These relatively small devices are a far cry from the 10 by 10-inch surface of the monolithic engraved silicon surface needed to make use of the optical field of view offered by MegaPrime, fitted to the Canada-France-Hawaii Telescope.

Today, the only cost- effective way to pave such large surface is to make a mosaic of state of the art detectors. The largest monolithic scientific optical detectors available are "stitched" closely together on their four sides on a single mechanical mount, reducing as much as possible the dead space between the sensitive surfaces. 
Each of the 40 e2v detectors (known as the ''CCD42-90'') seen in this photograph account for more than 9.5 megapixels, bringing the total number of pixels for the MegaCam mosaic to a staggering 377 million pixels!

Credit line: "Canada-France-Hawaii Telescope / 2003"

Copyright © 2003 Canada-France-Hawaii Telescope Corporation

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