... Science User Portal . ... ESO, the European Southern Observatory . ... Travel and Contacts . ... ESO Acronyms . ... When the Moon appears as a thin crescent in the twilight skies of Earth it is often possible to see that the rest of the disc is also faintly glowing. ... It is due to sunlight reflecting off the Earth and illuminating the lunar surface. ... By observing earthshine astronomers can study the properties of light reflected from Earth as if it were an exoplanet and search for signs of life...