Mapping the stars

The biggest ever map of the sky has been created. It includes the location and brightness of 1,142,000 stars, and two million of these also have their motion across the sky mapped.


Pictures from ESA’s Gaia satellite have been compiled by a team of 450 scientists and software engineers. The satellite is half way through its five year mission to collect data on billions of stars in the Milky Way, just 1% of all the stars in the galaxy. The pictures come from the first 14 months of the mission.

Soon, the team will release a new version of the map, including more of the stars that Gaia has imaged since the first 14 months of operation. However, there is so much data that the team is struggling to keep up and have asked the public for help. The map is already twenty times as large as the previous definitive guide, the Hipparcos Catalogue, and twice as precise.

Gaia is 10 meters wide when its solar panels are outstretched, and it spins slowing, scanning the sky, 11.5 million kilometres away from Earth. Its camera is powerful enough to work out the diameter of a human hair from a thousand kilometres away, and is coupled with two telescopes. Combining the data and images with data from the Hipparcos Catalogue is what allowed the team to work out the motion of two million stars, by separating the ‘parallax motion’ of the star – its apparent motion due to Earth orbiting the Sun – and the ‘proper motion’ – the star’s physical movement.

The map has already located 386 previously unknown stars, and 3,194 variable stars. Variable stars are useful as cosmic distance indicators because they shrink and swell in size creating regular brightness changes. The Andromeda galaxy can also be seen, and the Large and Small Magellanic Clouds, which are two dwarf galaxies orbiting the Milky Way. The brightest portion of the image is the Galactic Plane, which is the plane that the Milky Way lies in, in a spiral. There are also stripes and other artefacts present, but these are a result of how Gaia scans the sky, and will gradually fade out as more data is added over time.

So what next? The map is just the tip of the ice-burg, and shows that Gaia is operating correctly and is well on the way to charting the position, brightness and motion of one percent of the Milky Way’s stars. Over the rest of the mission the map will reach unprecedented detail and accuracy.


Science Daily, 15th September 2016, ‘Gaia’s billion star maps hints at treasures to come’, (accessed 24/09/2016)

Sarah Knapton, The Telegraph, 14th September 2016, ‘A billion stars of the Milky Way captured in astonishing space map of night sky’, (accessed 24/09/2016)

Jonathon Amos, BBC News, 14th September 2016, ‘Gaia space telescope plots a billion stars’, (accessed 24/09/2016)

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