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\t\t\t\t\t\t14\/02\/2024<\/span> Today, ESA\u2019s space telescope <\/b>Euclid<\/b>\u00a0begins its survey of the dark Universe. Over the next six years, Euclid will observe billions of galaxies across 10 billion years of cosmic history. Learn how the team prepared Euclid in the months after launch for this gigantic cosmic quest.<\/b><\/p>\n<\/div>\n Euclid, one of the most precise and stable space telescopes ever built, was launched on 1 July 2023.\u00a0During its first months in space, teams across Europe turned on, tested, and prepared the mission for routine science observations. However, these \u2018routine\u2019 science observations are no piece of cake.\u202f\u00a0<\/p>\n<\/p><\/div>\n One of Euclid\u2019s strengths is that it can\u00a0observe a large area of the sky in one shot. This is crucial for a mission whose primary objective is to map more than one third of the sky in six years.\u202f\u00a0<\/p>\n Euclid will follow a so-called \u2018step-and-stare\u2019 observation mode. This means that the telescope will stare at one area of the sky for about 70 minutes, producing images and spectra, and it then takes four minutes to move to the next area of the sky. During its entire mission, Euclid will perform more than 40 000 of these \u2018pointings\u2019.\u202f\u00a0<\/p>\n \u201cThanks to its wide-eyed look at the cosmos, and its long exposure time and sensitivity, the number of galaxies that Euclid can see in one pointing is huge,\u201d explains Roberto Scaramella, Euclid survey scientist at the National Institute for Astrophysics (INAF) in Italy, and lead of the consortium survey group since the beginning of the mission.\u202f\u00a0<\/p>\n<\/p><\/div>\n Roberto had to make sure that the survey was designed in such a way that it meets the science goals. A main goal for Euclid is to measure in more detail than ever before the shapes of billions of galaxies over billions of years of cosmic history, to provide a 3D view of the dark matter distribution in our Universe.\u202f\u00a0<\/p>\n \u201cTo study the individual distortions of galaxies by dark matter, we need to observe at least 1.5 billion galaxies. Euclid will observe the shapes of around 50 000 galaxies with the needed accuracy in one shot, and will spot many more faint ones,\u201d adds Roberto.\u202f\u00a0<\/p>\n However, soon after turning Euclid\u2019s instruments on for the first time, the team realised that the entire survey needed to be re-designed.<\/p>\n<\/p><\/div>\n The problem was that a tiny amount of unwanted sunlight was reaching Euclid’s visible instrument (VIS) at specific angles, even with the spacecraft\u2019s sunshield (its back) turned towards the Sun. \u00a0<\/p>\n \u201cThe original plan was for Euclid to keep its sunshield facing the Sun. But soon after launch, disturbing light from the Sun was detected in the test images,\u201d explains Ismael Tereno of the University of Lisbon, Portugal, and lead of the Euclid survey operations support team, operated with the support of the Portuguese Space Agency. \u00a0<\/p>\n \u201cAfter intense troubleshooting, science, engineering, and industrial teams found that for this light to disappear, Euclid needed to observe with a different orientation (attitude) with respect to the Sun. This meant that the original survey design would no longer work. We had to quickly come up with a new strategy, implement it, and test it,\u201d adds Jo\u00e3o Dinis, also from the University of Lisbon, Portugal who together with Ismael was responsible for the survey (re-)design. \u00a0<\/p>\n To minimise the effect of \u2018stray\u2019 sunlight, the teams found out that Euclid needs to observe with a more restricted rotation angle, such that the sunshield is not directly facing the Sun, with a small but impactful tilt in one direction. With this new restricted attitude, parts of the sky could not be reached from any point in Euclid\u2019s orbit around L2. \u201cIt proved very difficult to find a good survey solution, and we had to go back to the drawing board,\u201d recalls Ismael.\u00a0\u00a0<\/p>\n<\/p><\/div>\n It was the start of a very intense phase for Jo\u00e3o, Ismael and the survey operations and science teams. \u201cJo\u00e3o quickly had the insight of what needed to be changed, and then worked around the clock to propose a workable re-design,\u201d says Ismael. \u00a0<\/p>\n Designing the Euclid survey was a giant puzzle. Aside from the scientific goals and the angle that Euclid needed to observe from, there are many other factors that needed to be considered.\u00a0\u00a0<\/p>\n<\/p><\/div>\n The largest fraction of the mission’s observations will be devoted to a \u2018wide\u2019 survey, covering more than one third of the sky. The wide survey is complemented by a deep survey, taking about 10% of the total observing time. Aside from that, routine calibration observations also had to be scheduled to fit the puzzle.\u00a0<\/p>\n Xavier Dupac, ESA survey scientist for the Science Operation Centre at ESAC in Spain, made sure that the survey designed by Jo\u00e3o, Ismael and the team could be executed. \u201cFor example, we need to take into account the time it takes for the spacecraft to rotate from one observing position to the next. These times need to be included in the survey design in addition to the actual observing time,\u201d explains Xavier. \u00a0<\/p>\n In the end, the teams came up with a workable solution that meant more overlaps between adjacent observations had to be made. Euclid\u2019s survey is now slightly less efficient, but all necessary areas of the sky can be reached and the overall loss in survey area is kept to a minimum. \u00a0\u00a0<\/p>\n \u201cThe teams worked very hard to redesign the survey in a short amount of time, this is a major achievement,” says Valeria Pettorino, Euclid project scientist for ESA. \u201cAnd this is not the end of the story. As the mission advances and the scientific results start to arrive, the teams will continue to optimise the survey, and be ready to adapt it if needed.\u201d\u00a0<\/p>\n<\/p><\/div>\n Today, Euclid officially started its survey. The telescope is currently scheduled to observe a patch of 130 square degrees \u2013 more than 500 times the area of the full Moon \u2013 over the course of the next 14 days. This patch is in the direction of the constellations of Caelum and Pictor in the Southern Hemisphere.\u00a0\u00a0<\/p>\n In the coming year, Euclid will cover around 15% of its survey. This first year of cosmology data will be released to the community in summer 2026. A smaller data release of deep field observations is foreseen for spring 2025.\u00a0\u00a0<\/p>\n<\/p><\/div>\n Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium \u2013 consisting of more than 2000 scientists from 300 institutes in 13 European countries, the US, Canada and Japan \u2013 was responsible for providing the scientific instruments and will provide the scientific data analysis. ESA selected Thales Alenia Space as prime contractor for the construction of the satellite and its service module, with Airbus Defence and Space chosen to develop the payload module, including the telescope. NASA provided the detectors of the Near-Infrared Spectrometer and Photometer, NISP. Euclid is a medium-class mission in ESA\u2019s Cosmic Vision programme.\u00a0<\/p>\n For more information, please contact:\u00a0<\/b><\/p>\n \nESA Media Relations
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\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n<\/p><\/div>\n50 000 galaxies in one shot<\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nA change in attitude <\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\nA giant puzzle <\/h2>\n
\n\t\t\t\n\t\t<\/div>\n<\/p><\/div>\nLooking ahead at Euclid\u2019s first survey year <\/h2>\n
\n\t\t\t\t\t\t\t\t<\/figcaption><\/figure>\n About Euclid <\/h2>\n
Email: media@esa.int<\/p>\n<\/p><\/div>\n