On the occasion of the recent delivery of a new harvest of data from the European satellite Gaia, its scientific manager for France, François Mignard, evokes the origin of this instrument, and its major contribution to the cartography of the sky in the optical domain, the astronomy of visible light.
What characterizes the Gaia mission?
Gaia is a mission devoted to the field of astrometry. This branch of astronomy, whose origins date back to antiquity with the work of Hipparchus (190-120 BC) and Ptolemy (90-168), is dedicated to the measurement of position and the movement of the stars. It suffered for a long time from a lack of progress, until the reasons for this stagnation were understood in the 1960s. To precisely place a star on the celestial vault, it is necessary to have an image. However, the presence of the atmosphere creates disturbances that degrade its quality. Based on an idea by Pierre Lacroute, then director of the Strasbourg observatory, the discipline began to think about the possibility of sending an instrument into space. The construction of such equipment exceeding the financial and technical possibilities of a single state, a project was proposed to the European Space Agency, resulting in the launch of Hipparcos in 1989. Despite the engine problems it faced after After take-off, this satellite succeeded in measuring the distances of 120,000 previously selected stars. It was a huge success.
Subsequently, various European specialists, including myself, began to think about a much more ambitious mission: Gaia. It is necessary to realize the importance of this work of surveyor. Light is the only available source of information about stars. To deduce from the apparent brightness of a star its true or intrinsic luminosity, and therefore to acquire information on its physical properties, knowledge of its distance is essential!
What was the purpose of this launch?
Gaia could be likened to a service mission since its results are of interest to the entire community of astronomers. What this satellite does best is observe stars. This makes it the most suitable equipment for studying the Milky Way. By providing information on the life and characteristics of these stars, on the way their various populations organize themselves to form substructures, it can help to clarify the current composition of our galaxy, and to better understand its past evolution. or future. Gaia has all the tools necessary to achieve this goal. He can accurately measure the distances and movements of stars using his astrometric instrument. Specify their physical characteristics thanks to its double photometer. And, to determine their chemical compositions and their speeds of separation or approach by using its spectrograph.
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