ESA’s Gaia satellite is a feat of optical engineering. The “star hunter” identified the brilliance and precise position of 1.7 billion stars and determined their distance and speed of movement in the sky for 1.35 billion of them. Allowing for breathtaking modeling.
Since 2012, this insatiable celestial surveyor, who accompanies us in our race around the Sun 1.5 million km from the Earth, measures every second the positions of 5000 stars, scanning the entire sky. Wednesday, the European Space Agency (ESA) has unveiled an unparalleled map of 1.7 billion light points in the sky.
This astronomical figure is more than the number points a human with naked eye can actually detect. Indeed, humans can not distinguish more than 3000 “points” in the purest and clearest starry sky. Gaia detected 500,000 times more, characterizing their brightness and their position in the sky with diabolical precision.
Its exceptional instruments, a million times more sensitive than our retina, also allow it to distinguish 1000 km apart, two points separated by the thickness of a hair. It did not take less to succeed in detecting the tiny ellipses that describe the stars in the sky as the Earth revolves around the Sun. These microscopic movements are all the more important as the stars are close to us, which allows us to deduce their distance, by a simple geometric rule. Gaia was able to measure the distance that separates us from 1.35 billion stars.
This is not a vulgar world map, but a three-dimensional map that has just been drawn and an animated map. The stars also move in relation to each other.
If these displacements are tiny on the scale of a human life, they nonetheless affect the shape of our constellations over tens of thousands of years. We now know these speeds of movement for each of these 1.35 billion stars. And for a “small” part of them, more than 7 million all the same, astronomers have managed to measure their “radial” speed, that is to say the rate at which they are getting closer or farther from us (the researchers rely for this on the “color” of the star that shifts towards blue or red by the Doppler effect, in the same way that the sound of an approaching ambulance is more acute than that of an ambulance moving away).