MUSE spectrograph reveals that nearly the entire sky in the early Universe is glowing with Lyman-alpha emission

Deep observations made with the MUSE spectrograph on ESO's Very Large Telescope have uncovered vast cosmic reservoirs of atomic hydrogen surrounding distant galaxies. The exquisite sensitivity of MUSE allowed for direct observations of dim clouds of hydrogen glowing with Lyman-alpha emission in the early Universe--revealing that almost the whole night sky is invisibly aglow.