WHAT EUCLID WILL MEASURE: WEAK 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.

Euclid will measure the distorted shapes of billions of galaxies over 10 billion years of cosmic history, 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.