Scientists are tapping into photographs taken by astronauts aboard the International Space Station (ISS) to reliably measure the amount of light pollution worldwide. This study not only includes the well-known signatures of cities and streets, but also the effects of faint indirectly scattered light, which up to now had not been measured quantitatively. The new results confirm that this diffuse glow, which is seen from space, is scattered light from streetlights and buildings. This is the component responsible for the brightening of the night skies in and around cities, which drastically limits the visibility of faint stars and the Milky Way.