What Euclid will measure: weak lensing

To understand more about the dark Universe, ESA’s Euclid will measure a phenomenon known as ‘weak lensing’, based on the principle of gravitational lensing.

A concentration of matter along the line of sight can act like a magnifying glass, bending and distorting light from galaxies and clusters behind it. This effect is called gravitational lensing. Scientists distinguish between strong gravitational lensing, when the distortions are very apparent, like in the case of Einstein rings, arcs and multiple images, and weak gravitational lensing, when the distortions of background sources are much smaller. In this case, distortions (of a few percent) can only be detected by analysing large numbers of sources in a statistical way.

ESA’s Euclid will measure the distorted shapes of billions of galaxies over 10 billion years of cosmic history, thus providing a 3D view of the dark matter distribution in our Universe.

The map of the distribution of galaxies over cosmic time will also teach us about dark energy, which affects the spatial evolution of the large-scale structure.

Euclid is a European mission, built and operated by ESA, with contributions from NASA. The Euclid Consortium is responsible for providing the scientific instruments and 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.