Ready set, go! ESA’s space telescopeEuclid begins its dark universe survey

Euclid, one of the most precise and stable space telescopes ever built, was launched on 1 July 2023. During its first months in space, teams across Europe turned on, tested, and prepared the mission for routine science observations. However, these ‘routine’ science observations are no piece of cake.  

(Cover imagine by ESA: Euclid's survey in the next six years)

50 000 galaxies in one shot

One of Euclid’s strengths is that it can observe 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.  

Euclid will follow a so-called ‘step-and-stare’ 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 ‘pointings’.  

“Thanks 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,” 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.  

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.  

“To 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,” adds Roberto.  

However, soon after turning Euclid’s instruments on for the first time, the team realised that the entire survey needed to be re-designed.

Looking ahead at Euclid’s first survey year

On14^th Febryary, Euclid officially started its survey. The telescope is currently scheduled to observe a patch of 130 square degrees – more than 500 times the area of the full Moon – 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.  

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.

About Euclid

Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium – consisting of more than 2000 scientists from 300 institutes in 13 European countries, the US, Canada and Japan – 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’s Cosmic Vision programme. 

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