Glowing hydrogen (blue) as detected with the MUSE spectrograph around galaxies. Image: ESA/Hubble & NASA, ESO/ Lutz Wisotzki et al.
The night sky is glowing, but you cannot see it - space science news

With the aid of the MUSE spectrograph on ESO’s Very Large Telescope, astronomers have observed abundant Lyman-alpha emission (a spectral line of hydrogen) around distant galaxies. This observation was only possible because of improved sensitivity of the spectrograph to detect dim hydrogen glowing. The hydrogen clouds, the first building blocks of the universe, were observed in the constellation of Fornax, that has been mapped by the Hubble telescope in 2004. Extrapolation of the data indicate that most of the night sky is invisibly aglow.

Read the full story: European Southern Observatory (ESO)
Scientific publication: Nature