Weak gravitational lensing
Illustration of one of the two primary cosmological probes of Euclid: weak gravitational lensing.
The distribution of dark matter measured from the HST COSMOS survey using weak gravitational lensing. This survey covers an area about 8 times the size of the Moon. Euclid will produce higher resolution 3-D dark matter maps over the entire sky.
(The second Euclid cosmological probe is Baryonic Acoustic Oscillations.)