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The motion of two million stars

The motion of two million stars

This extraordinary video from European Space Agency reveals the changing face of our Galaxy, tracing the motion of two million stars five million years into the future using data from the Tycho-Gaia Astrometric Solution, one of the products of the first Gaia data release.

This provides a preview of the stellar motions that will be revealed in Gaia’s future data releases, which will enable scientists to investigate the formation history of our Galaxy.

The stars are plotted in Galactic coordinates and using a rectangular projection: in this, the plane of the Milky Way stands out as the horizontal band with greater density of stars.

The video starts from the positions of stars as measured by Gaia between 2014 and 2015, and shows how these positions are expected to evolve. The frames in the video are separated by 750 years, and the overall sequence covers five million years. The stripes visible in the early frames reflect the way Gaia scans the sky and the preliminary nature of the first data release; these artefacts are gradually washed out in the video as stars move across the sky.

The shape of the Orion constellation can be spotted towards the right edge of the frame, just below the Galactic Plane, at the beginning of the video. As the sequence proceeds, the familiar shape of this constellation (and others) evolves into a new pattern. Two stellar clusters – groups of stars that were born together and consequently move together – can be seen towards the left edge of the frame: these are the alpha Persei (Per OB3) and Pleiades open clusters.

Two million stars from TGAS sample ESA/Gaia/DPAC

Our photograph is an all-sky view of the 2 057 050 stars from the Tycho-Gaia Astrometric Solution (TGAS), one of the products of the first data release from ESA’s Gaia mission. TGAS lists positions, distances and proper motions for stars in common between Gaia’s first year and the earlier Hipparcos and Tycho-2 Catalogues, both derived from ESA’s Hipparcos mission, which charted the sky more than two decades ago. The view also includes 24 320 bright stars from the Hipparcos Catalogue that are not included in Gaia’s first data release.

The stars are plotted in Galactic coordinates and using a rectangular projection: in this, the plane of the Milky Way stands out as the horizontal band with greater density of stars.

The shape of the Orion constellation is highlighted towards the right edge of the frame, just below the Galactic Plane. Two stellar clusters can be seen towards the left edge of the frame: these are the alpha Persei (Per OB3) and Pleiades open clusters.

In this view, brighter stars are shown as larger circles, and an indication of the true colour of each star is also provided; information about brightness and colour is based on the Tycho-2 catalogue from the Hipparcos mission. The stripes visible in the image reflect the way Gaia scans the sky and the preliminary nature of the first data release.