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Gaia satellite begins 3D-mapping the galaxy

​The largest digital camera ever sent into space is beginning its quest to map the Milky Way, surveying a billion stars with nearly a billion pixels.

The Gaia satellite operates two telescopes simultaneously. European Space Agency

Having launched into space in December 2013, the European Space Agency's Gaia satellite is now 1.5 million kilometres from Earth and ready to begin its mission to map our galaxy.

Gaia will use a gigapixel camera -- ie it has nearly 1,000 megapixels -- to measure the positions and motions of roughly 1 percent of the galaxy's 100 billion stars, as well as measuring other properties such as brightness, temperature and chemical composition.

"Repeatedly scanning the sky, Gaia will observe each of its billion stars an average of 70 times each over five years," the ESA said in a statement. "Small apparent motions in the positions of the stars will allow astronomers to determine their distances and movements through the Milky Way.

"Gaia spins slowly once every six hours, sweeping its two telescopes across the sky and focusing the light from their separate fields simultaneously onto a single focal plane -- the largest digital camera ever flown in space, with nearly a billion pixels."

Light travels from Gaia's telescopes to a single focal plane. European Space Agency

Since launching from French Guiana on the northern edge of South America last year, Gaia has encountered a number of problems, including frozen water on parts of the optics and 'stray light' finding its way past the satellite's sunshield and reaching the focal plane "at a level higher than predicted before launch".

After extensive calibration, however, Gaia can now begin its work. It will individually map stars and measure their relative positions creating a complete star network that will become a "highly accurate 3D map" of the skies. Throughout its five-year mission, the satellite will measure an average of 2 million stars every hour, generating roughly 50GB of data every day.

According to the ESA, this work requires "astonishing" accuracy -- as it journeys through space, "Gaia must be able to measure positions to a level equivalent to the width of a human hair seen at 2,000 kilometres".