Mapping the Milky Way with Gaia

Latest ESA Euronews video looks at Gaia and explains how it will scan the sky with powerful new eyes, mapping the Milky Way in unprecedented detail.



  • 8:45 / Carme Jordi asks “Do we have two, three, four arms in our Galaxy?”

    Definitely two:

    I am looking forward to exploring Gaia data releases in the not-too-distant future.

    • mareike says:

      That’s an interesting question! In fact, Astronomers are still not certain of how many arms our galaxy has.
      So far, we know only the basics: That the Milky Way is shaped something like a fried egg, with a bulge of stars in the middle surrounded by a flat stellar disk that tapers at the edges and contains the Galaxy’s spiral arms. Around the disk is a diffuse sphere of old stars called the halo. But astronomers are not certain how these structures formed, or in what order. Gaia will provide one important set of clues by measuring stellar composition and brightness — data that will reveal for the first time when many stars formed, and will help astronomers to work out the ages of the Galaxy’s different parts (see Nature article).
      More info about Gaia at:

      • Thanks for replying, Mareike. It’s true that astronomers are collectively divided on the issue of the # of spiral arms, but in the papers cited above, we believe that a careful discernment of Hipparcos, HII, and 2MASS data gives us confidence to venture a prediction for a two-arm model with a 5.5-degree pitch angle. Will Gaia vindicate us? Time will tell!

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