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gaiaHere on Earth we play around with CCD cameras that boast a million pixels. But, can you imagine what a billion pixels could do? That’s the plan for ESA’s Galaxy-mapping Gaia mission. One hundred six electronic plates are being carefully integrated together to add up to the largest digital camera ever built for space… and its mission is to chart the Milky Way. Beginning in 2013, Gaia’s five year mission will be to photograph a billion stars within our own galaxy – determining magnitude, spectral characteristics, proper motion and dimensional positioning. This information will be gathered by its charge coupled device (CCD) sensor array.

Each of the 106 detectors are smaller than a normal credit card and thinner than a human hair. Put simplistically, each plate holds its own array of light-sensitive cells called photosites. Each photosite is its own pixel – just one tiny cell in the whole body of a photograph that could contain hundreds of thousands of pixels! When incoming light strikes the photosite, the photoelectric effect occurs and creates electrons for as long as exposure occurs. The electrons are then kept “stored” in their individual cells until a computer unloads the array, counts the electrons and reassembles them into the “big picture”.

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