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Launch of the astrometric satellite GAIA

Following the success of the astrometric satellite Hipparcos, scientists realized that they could do still better. That is what the European satellite GAIA is doing: It is measuring the positions of millions of stars with a precision of 10-millionths of a second of arc, 100 times better than Hipparcos, and is also cataloguing a billion stars with somewhat less precision. Repeated observations enable the determination of the transverse motion of stars (their “proper motions”), while a spectrograph on board measures their motions along the line of sight (the “radial velocity”) via the Doppler-Fizeau effect of their spectral lines. In this way, the three velocity components of the stellar velocity are thus found. A photometer follows the stellar brightness changes, which are often due to the transit of a planet in front of the stellar disc. It is hoped that with the help of GAIA about 30,000 exoplanets will be discovered, adding to the 3,500 known today.

caption : Preparing for the launch of Gaia - credits : ESA/CNES/Arianespace