Northern sky survey takes its first shot at dark matter clustering

Using 3,500 square degrees of deep r-band imaging, the UNIONS team measures how foreground matter distorts background galaxy shapes to constrain S8, the amplitude of matter clustering, obtaining S8 = 0.831 (+0.067/−0.078). The result sits within one sigma of both Planck CMB measurements and earlier weak lensing surveys, offering no evidence for the tension sometimes reported in other datasets. The analysis uses a single tomographic bin and two-point correlation functions, with careful treatment of PSF systematics and shear calibration. It establishes UNIONS as a competitive northern-hemisphere lensing survey ahead of Stage IV experiments like LSST and Euclid.