The European Space Agency will unveil a three dimensional map of a billion stars in our galaxy that is 1,000 times more complete than anything existing today. A space based probe called Gaia, launched in December 2013, has been circling the Sun 1.5 million kilometres (nearly a million miles) beyond Earth's orbit and has been discreetly snapping pictures of the Milky Way. The satellite's billionpixel camera, the largest ever in space, is so powerful it would be able to gauge the diameter of a human hair at a distance of 1,000 kilometres, meaning nearby stars have been located with unprecedented accuracy.
Just over halfway through its fiveyear mission, Gaia's two telescopes have located a billion stars. That's still only one percent of the Milky Way's estimated stellar population, scattered over an area 100,000 light years in diameter. But it is enough to keep professional stargazers busy for years to come.
Gaia maps the position of the Milky Way's stars in a couple of ways. Not only does it pinpoint their location, the probe by scanning each star about 70 times can plot their movement as well. This is what allows scientists to calculate the distance between Earth and each star, a crucial measure. Both types of data will be available for more than two million stars. By the end of 2017, Gaia will have done the same for a billion. At the same time, it will collect vital data about each star's temperature, luminosity and chemical composition, vastly expanding current knowledge.
Gaia’s main scientific goal is to unravel the structure and dynamics of the Milky Way in order to shed light on the violent history of our galaxy. Some of its stars were born within smaller galaxies, which were later cannibalized by our monstrous galaxy. Today the remnants of those puny galaxies can be seen in the form of faint streams of stars that stretch across the sky. Tens of thousands of previously undetected objects will be discovered, including asteroids that may one day threaten Earth, planets circling nearby stars, and exploding supernovas. By identifying stars from smaller galaxies long ago swallowed up by our own, Gaia will also help scientists better understand the Milky Way's origin and evolution.
Astrophysicists, meanwhile, hope to learn more about the distribution of dark matter, the invisible substance thought to hold the observable universe together. They also plan to test Albert Einstein's general theory of relativity by watching how light is deflected by the Sun and its planets.
The spacecraft is controlled from the European Space Operations Centre in Darmstadt, Germany, using ground stations in Cebreros, Spain and New Norcia in Australia. More than 50 companies across Europe were involved in building Gaia and its instruments.
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Mapping the galaxy
• Gaia observed one billion stars about 70 times each over five years. That’s an average of 40 million observations a day!
• One billion stars amounts to about one percent of the stars populating the Milky Way.
• Of the one billion stars Gaia will observe, 99% have never had their distances measured accurately.
• Gaia will carry the largest digital camera into space with nearly one billion pixels. By comparison, smart phone cameras have around 10 million pixels.
• Gaia will detect celestial objects that are a million times fainter than the unaided human eye can see.
• For objects 4000 times fainter than the naked eye limit, Gaia will measure their positions to an accuracy of 24 microarcseconds, comparable to measuring the diameter of a human hair at a distance of 1000 km. Gaia’s predecessor, Hipparcos, could have measured the diameter of a human hair at a distance of 20 km.
• The nearest stars will have their distances measured to the extraordinary accuracy of 0.001%. Even stars near the Galactic Centre, some 30 000 lightyears away, will have their distances measured to within an accuracy of 20%.
• The Gaia Data Processing and Analysis Consortium (DPAC) consists of more than 400 individuals who will contribute some 2000 personyears of effort to the Gaia data processing exercise.
• By the end of the mission, the data archive will exceed 1 Petabyte (1 million Gigabytes), equivalent to about 200 000 DVDs worth of data.
• With two primary mirrors that can collect 30 times the amount of light as Hipparcos and a camera that has a resolution over 50 times greater than the one onboard the Hubble Space Telescope, it is no wonder astronomers are excited
