The Astronomy Thread

Launched in December 2013, Gaia is destined to create the most accurate map yet of the Milky Way. By making accurate measurements of the positions and motions of stars in the Milky Way, it will answer questions about the origin and evolution of our home galaxy.

The first intermediate data release, containing among other things three-dimensional positions and two-dimensional motions of a subset of two million stars, demonstrates that Gaia’s measurements are as precise as planned, paving the way to create the full map of one billion stars to be released towards the end of 2017.

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A visualisation of how Gaia scanned the sky during its first 14 months of operations, between July 2014 and September 2015.The oval represents a projection of the celestial sphere, with different portions of the sky gradually appearing, according to when and how frequently they were scanned by Gaia.

The satellite scans great circles on the sky, with each scan lasting about 6 hours. During the first month, the scanning procedure was such that the ecliptic poles were always included. This meant that Gaia observed the stars in those regions many times, providing an invaluable database for the initial calibration of the observations.

Then, starting on 21 August 2014, the satellite started its main survey, employing a scanning 'law' designed to achieve the best possible coverage of the whole sky.

Data collected over Gaia's first 14 months make up the mission's first data release. Based on these observations, scientists produced a map of the sky, showing the density of stars observed by Gaia. Brighter regions indicate denser concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed.

The Galactic Plane, where most of the Milky Way's stars reside, is visible as the brightest portion of the map: a horizontal strip that is especially bright at the centre. Darker regions across the Galactic Plane correspond to dense clouds of interstellar gas and dust that absorb starlight along the line of sight.

Stellar clusters also appear, sprinkled across the image alongside a handful of nearby galaxies – most notably the Large and Small Magellanic Clouds in the lower right.

A number of artefacts, reflecting Gaia's scanning law, are also visible on the all-sky map. As this map is based on observations performed during the mission's first year, the survey is not yet uniform across the sky. These artefacts will gradually disappear as more data are gathered during the five-year mission.

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A virtual journey, from our Solar System through the Milky Way, based on data from the first release of ESA's Gaia satellite.

The journey starts by looking back at the Sun, surrounded by its eight planets. We then move away from the Sun and travel towards and around the Hyades star cluster, the closest open cluster to the Solar System, some 150 light-years away.

The 3D positions of the stars shown in the animation are drawn from the Tycho-Gaia Astrometric Solution (TGAS), which combines information from Gaia's first year of observations with the earlier Hipparcos and Tycho-2 Catalogues, both based on data from ESA's Hipparcos mission.

This new dataset contains positions on the sky, distances and proper motions of over two million stars. It is twice as precise and contains almost 20 times as many stars as the previous reference for astrometry, the Hipparcos Catalogue.

The journey continues showing the full extent size of the stars contained in the Tycho-Gaia Astrometric Solution, all relatively near to the Sun, in the overall context of our Milky Way galaxy.

The final Gaia catalogue will contain the most detailed 3D map ever made of the Galaxy, charting a billion stars – about 1% of the Milky Way's stellar content – to unprecedented accuracy.

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