Spot Gaia to get the most accurate map ever seen of more than a billion stars

Gaia, operated by the European Space Agency (ESA), examines the sky from orbit to create the largest and most accurate three-dimensional map possible. Our mission, a year ago, released its much-anticipated second data release, which included High Precision Measurements (Positions, Distances, and Clean Movements) of more than a billion stars in our Milky Way galaxy , have studied the transformation in many areas of astronomy, addressing the structure, origin and evolution of the Milky Way and generating more than 1700 scientific publications since its launch in 2013.

In order to achieve the accuracy needed for Gaia's sky charts, it is essential to determine the position of the probe from the Earth. Therefore, while Gaia scans the sky and collects data for its stellar census, astronomers regularly monitor its position with the help of a global network of optical telescopes, including the VST of the US. Observatory Paranal of the ESO. The VST is currently the largest observation telescope observing the sky in visible light. He records Gaia's position in the sky every second night of the year.

"Gaia's observations require a special observation procedure," says Monika Petr-Gotzens, who coordinates Gaia's observations by ESO since 2013. "The spaceship is what we let's call it a "moving target" because it moves quickly in relation to the background star – follow Gaia is a challenge! "

"The VST is the perfect tool for choosing Gaia's motion," explained Ferdinando Patat, head of the ESO's Office of Observations Programs. "The use of one of ESO's first-rate ground facilities to enhance advanced space observations is a fine example of scientific cooperation."

"This is an exciting ground-space collaboration, which uses one of ESO's world-class telescopes to anchor the pioneering observations of the giant geometer from ESA." ", commented Timo Prusti, scientific director of Gaia project at ESA.

VST observations are used by ESA flight dynamics experts to track Gaia and fine-tune the knowledge of the spacecraft's orbit. Careful calibration is required to transform the observations, in which Gaia is only a grain of light among the bright stars, into significant orbital information. Data from the second version of Gaia were used to identify each of the stars in the field of view and allowed the spacecraft position to be calculated with astonishing accuracy – up to 20 milliarcseconds.

"It is a difficult process: we use Gaia 's star measurements to calibrate the position of his ship and ultimately improve his star measurements," says Timo Prusti.

"After a long and careful data processing, we have now reached the precision required for Gaia's ground observations to be implemented as part of the orbit determination," said Martin Altmann, campaign manager Ground Optical Tracking (GBOT) of the Astronomy Center of the University of Heidelberg, Germany.

The GBOT information will be used to improve our knowledge of Gaia's orbit not only in future observations, but also for all data collected from Earth in previous years, which will improve data products that will be included in the future. releases.

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