ESA Gaia coming into focus - NGC1818

An ESA Gaia test image of the young star cluster NGC1818 in the Large Magellanic Cloud, taken as part of calibration and testing before the science phase of the mission begins.

The field-of-view is 212 x 212 arcseconds and the image is approximately oriented with north up and east left. 

The integration time of the image was 2.85 seconds and the image covers an area less than 1% of the full ESA Gaia field of view.

Gaia's overall design is optimised for making precise position measurements and the primary mirrors of its twin telescopes are rectangular rather than round.

To best match the images delivered by the telescopes, the pixels in Gaia's focal plane detectors are then also rectangular. 

To produce this image of NGC1818, the image has been resampled onto square pixels. 

Furthermore, to maximise its sensitivity to very faint stars, Gaia's main camera does not use filters and provides wide-band intensity data, not true-colour images.

The false-colour scheme used here relates to intensity only. The real colours and spectral properties of the stars are measured by other Gaia instruments. 

Image courtesy ESA /DPAC /EADS Airbus DS.

ESA's billion-star surveyor Gaia is slowly being brought into focus.

This test image shows a dense cluster of stars in the Large Magellanic Cloud, a satellite galaxy of our Milky Way.

Once Gaia starts making routine measurements, it will generate truly enormous amounts of data.

To maximise the key science of the mission, only small 'cut-outs' centred on each of the stars it detects will be sent back to Earth for analysis.

This test picture, taken as part of commissioning the mission to 'fine tune' the behaviour of the instruments, is one of the first proper 'images' to be seen from Gaia, but ironically, it will also be one of the last, as Gaia's main scientific operational mode does not involve sending full images back to Earth.

Gaia was launched on 19 December 2013, and is orbiting around a virtual point in space called L2, 1.5 million kilometres from Earth.

Annotated diagram of the Payload Module

Gaia's goal is to create the most accurate map yet of the Milky Way.

It will make precise measurements of the positions and motions of about 1% of the total population of roughly 100 billion stars in our home Galaxy to help answer questions about its origin and evolution.

Repeatedly scanning the sky, Gaia will observe each of its billion stars an average of 70 times each over five years.

In addition to positions and motions, Gaia will also measure key physical properties of each star, including its brightness, temperature and chemical composition.

To achieve its goal, Gaia will spin slowly, sweeping its two telescopes across the entire sky and focusing the light from their separate fields simultaneously onto a single digital camera - the largest ever flown in space, with nearly a billion pixels.

But first, the telescopes must be aligned and focused, along with precise calibration of the instruments, a painstaking procedure that will take several months before Gaia is ready to enter its five-year operational phase.