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From an ESA press release, September 14, 2016 :

The first catalogue of more than a billion stars from ESA’s Gaia satellite was published on September 14, 2016 – the largest all-sky survey of celestial objects to date.

On its way to assembling the most detailed 3D map ever made of our Milky Way galaxy, Gaia has pinned down the precise position on the sky and the brightness of 1.142 billion stars. As a taster of the richer catalogue to come in the near future, this data release also features the distances and the motions across the sky for more than two million stars.

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Credit: ESA/Gaia/DPAC

The map projection above shows an all-sky view of stars in the Milky Way and our neighboring galaxies, based on the first year or so of Gaia’s observations. It shows the density of stars observed by Gaia in each portion of the sky. Brighter regions indicate denser concentrations of stars, while darker regions correspond to patches of the sky where fewer stars are observed. Darker regions across the Galactic Plane correspond to dense clouds of interstellar gas and dust that absorb starlight along the line of sight. Many globular and open clusters – groupings of stars held together by their mutual gravity – are also sprinkled across the image.

Note that the faint curved features and dark stripes are not of astronomical origin but rather reflect Gaia’s scanning procedure. 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.

Links: ESA press release, Gaia sky map.

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There is an error in the equation in the right-hand column relating the apparent magnitude and brightness of stars. In this equation, 2.512 should be raised to a power equal to (mB–mA), not merely multiplied by it. The formula should read:

bA = 2.512(mB-mA) × bB

The European Space Agency’s billion-star surveyor, Gaia was launched into space on Thursday December 19, 2013, where it will embark on its mission to create a highly accurate 3D map of our galaxy. (See pp. 285, 290.)

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Credit: ESA

By repeatedly observing a billion stars, with its billion-pixel video camera, the Gaia mission will allow astronomers to determine the origin and evolution of our galaxy whilst also testing gravity, mapping our inner Solar System, and uncovering tens of thousands of previously unseen objects, including asteroids in our Solar System, planets around nearby stars, and supernovae in other galaxies.

Gaia will map the stars from an orbit around the Sun, near a location some 1.5 million km beyond Earth’s orbit known as the L2 Lagrangian point. The spacecraft will spin slowly, sweeping its two telescopes across the entire sky and focusing their light simultaneously onto a single digital camera, the largest ever flown in space. The ‘eye’ of Gaia’s camera has the most sensitive set of light detectors ever assembled for a space mission.

Once Gaia starts routine operations, in late Spring 2014, astronomers will have the challenge of dealing with a flood of data. Even after being compressed by software, the data produced by the five-year mission will fill over 30,000 CD-ROMs!

The first Gaia science is expected to be discoveries of new sources – supernovae, extreme variable stars, and blazars.

Links: University of Leicester press release; ESA launch campaign blog and press release; ESA lift-off movie.