The promise of the European Gaia mission had been no small one.

Nothing less than revolutionizing our understanding of the Milky Way was the plan when the space observatory was sent in 2013 to the L2 Lagrange point of the Sun-Earth-Moon system, about 1.5 million kilometers away.

Three years later, when the European Space Agency ESA presented the first data in September 2016, the project scientist Timo Prusti once again put into words the special nature of this task: Observing our galaxy is equally easy and difficult.

Simple, because wherever you look in the sky, you can see their stars.

Difficult, because since we are in the middle of it, one would really have to carefully examine all objects in every direction to get a complete picture.

Confirmation from personal observation is easy: when we see the band of the Milky Way in the sky on dark nights, it seems anything but obvious that this is actually a disk seen from the side with spiral arms and all sorts of structures.

Gaia's main task was and is to determine the three-dimensional positions and movements of several billion stars in our galaxy and thus give us a view of our Milky Way from the outside - a perspective that will never be possible for us directly.

Sibylle Anderl

Editor in the feuilleton, responsible for the "Nature and Science" department.

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The first, still incomplete data release from 14 months of observation had already shown that Gaia would be able to keep the promise.

The first results on the structure and history of our Milky Way based on the distances and proper motions of around two million stars were already so extraordinary and diverse that astronomers around the Dutch Amina Helmi called their first galactic Gaia study a "box full of chocolate": There was something for almost every astronomical taste.

She and her colleagues had found evidence in the data that the old stars in the halo of the Milky Way, the spherical area around the galactic disk, had once been added to our galaxy in the course of mergers with other galaxies.

The range of flavors was then significantly expanded again in the second data release in 2018.

The number of sources determined with regard to their position in space and their proper motion on the celestial sphere had increased from two million to more than a billion. In addition, additional information such as the radial velocity parallel to the line of sight or their brightness and color was available for some of the sources.

In December 2020, the "early" third data release followed with a further increase in the number of stellar sources and more precise astrometric data.

However, astronomers around the world had to wait a little longer for the complete treasure trove of data from 34 months of observations – until now.