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English: By observing more than a third of the sky during its mission, ESA’s Euclid will provide a gigantic catalogue of billions of galaxies and stars. This will be a treasure trove of data that can be used to improve our understanding of many aspects of astronomy: from merging galaxies to the physics of small and cool stars.
Euclid has a four times higher resolution, and 15 times better sensitivity in the near-infrared than is possible from current ground-based surveys. For each galaxy in Euclid’s detailed three-dimensional map, we will know its shape, mass, and other properties such as an estimate of how many new stars it produces per year.
In the ‘nearby’ Universe, out to a distance of around 16 million light-years, Euclid will even be able to see which types of stars each galaxy hosts, and how these stars orbit around their galaxy centre. This will teach us about how different galaxies form.
Although the largest fraction of its observations will be devoted to a wide survey, Euclid will spend about ten percent of its time looking at just three patches of the sky. These regions are called the Euclid Deep Fields. By staring at these patches, Euclid will be able to see objects that are hundreds of times fainter than the ones ESA’s Gaia can detect. Two of these regions were chosen to overlap with Hubble ‘deep field’ measurements, while the third has been specially selected for Euclid.
Since 2013, ESA's Gaia mission has been producing a gigantic survey of almost two billion stars in the Milky Way. Euclid will augment this survey. Unlike Gaia, Euclid will also observe near-infrared light and will be able to spot the brown dwarfs and ultra-cool stars that Gaia will miss.
In addition to detecting new objects, Euclid will provide complementary information for stars that have already been observed by Gaia. It will measure infrared colours and spectra for these objects. This new information will allow astronomers to calculate the precise age and initial chemical composition of each star. This is crucial for determining how the heavier chemical elements have built up in our galaxy.
Euclid is ESA’s space telescope designed to explore the dark Universe. The mission will create the largest, most accurate 3D map of the Universe ever produced across 10 billion years of cosmic time. Euclid will explore how the Universe has expanded and how large-scale structure is distributed across space and time, revealing more about the role of gravity and the nature of dark energy and dark matter.