Space
The European Space Agency is about to reveal a three dimensional map of a billion stars in our galaxy collected from the Gaia mission. The data should give us a picture of the Milky Way that is 1,000 times more complete than anything we have today.
The Gaia spacecraft is the European Space Agency's mission to compile the most detailed three dimensional map ever made of our Milky Way galaxy. The spacecraft's mission involves charting one percent of the galaxy, about billion stars. This first data dump will open a new chapter in astronomy, according to the agency.
Gaia houses two telescopes, using ten mirrors of different shapes and sizes to collect, focus and direct light onto Gaia's sensor. On the focal plane, are three science instruments: the astrometric instrument, the photometric instrument and the radial velocity spectrograph.
With a total of 106 CCD detectors and almost one billion pixels, Gaia's camera is the largest ever flown into space.
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Launched on 19 December 2013 on a Soyuz-STB/Fregat-MT launch vehicle from Europe's spaceport in Kourou, French Guiana, Gaia traveled to its orbit around the Lagrangian point L2, 1.5 million km further from the Sun than Earth. Now one thousand days after launch, the mission will release its first set of data.
The map (shown above) shows the density of stars observed by Gaia in each portion of the sky. Brighter regions indicate denser concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed. The Milky Way is a spiral galaxy, with most of its stars residing in a disc about 100 000 light-years across and about 1000 light-years thick. This structure is visible in the sky as the Galactic Plane – the brightest portion of this image –which runs horizontally and is especially bright at the center.
This first Gaia data release contains a catalogue of 1,140,622,719 stars with precise measurements of their position on the sky and brightness.
From the first year of Gaia's observations alone, it is not possible to separate two concurrent effects in the changes of stellar positions recorded by the satellite: the apparent annual shift caused by Earth's motion around the Sun, or parallax, which is inversely proportional to a star's distance, and the continuous motion across the sky as stars drift through the galaxy.
With the data, it has been possible to estimate the distance from us and the proper motion for the 2,057,050 stars in common with the earlier Hipparcos and Tycho-2 Catalogues, based on data from ESA's Hipparcos mission.
In addition, the data release also contains 3194 variable stars, including details about their brightness variations. Variable stars periodically change their brightness as they rhythmically swell and shrink in size leading to periodic brightness changes.
On a typical day, Gaia performs about 637 million astrometric measurements, 155 million photometric measurements, and 13 million spectrometric measurements. These correspond to roughly 70 million celestial objects transiting the spacecraft's focal plane. Every day, Gaia sends about 40 GB of data back to Earth.
The spacecraft has recorded over 50 billion source transits over its focal plane so far, more than 110 billion photometric observations, and almost 10 billion spectra. Six data processing centers are involved in the data challenge, and about 120 000 hours of computations have so far been necessary to identify sources in the data collected by the spacecraft and associate them with the corresponding object in the sky.
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