The light pollution that shrouds cities and regions in the night causes the majority of the stars to disappear that would otherwise be visible to the naked eye. Of the approximately 3000 stars that can be observed in a dark night sky, less than a hundred are visible in a brightly lit city (often significantly less).
Today, 83 percent of the world's population and 99 percent of Europeans live under light-polluted skies. For 60 percent of Europeans, the Milky Way is hidden from view.
Big cities create a sky glow that is visible at a distance of up to 160 km.
Light pollution is now so severe that the darkest areas of Europe are twice as bright as they would be under natural conditions.
The atmosphere scatters blue light much more than red light. That is why the cloudless daytime sky is blue (Rayleigh scattering). Short-wave or blue light sources are therefore intensive light pollutants and should be avoided as far as possible.
Night skies over Mongolia, a rural area in Lower Austria and Vienna. About 200 years ago, the night sky over Vienna was no different from that in Mongolia today.
The view of the starry sky is one of mankind's earliest cultural assets. Whereas it was initially used to determine the time and create calendars, the stars in the sky later came to play a prominent role for navigation at sea.
Centuries of observation of the phases of the moon and signs of the zodiac have yielded insights for planting and harvesting in agriculture and for other areas of daily life that are still valid today.
Since the advent of artificial outdoor lighting at around the end of the 19th century, light blight has made it increasingly difficult to observe the night sky. The observatories that were originally attached to the universities in the cities relocated to rural areas. The most prominent observatories were built in remote locations. The world’s biggest telescope, for example, is to be found in Chile’s Atacama Desert. Observatories permit processes to be observed in the sky that cannot be simulated in the laboratory. Professional astronomy is an important part of basic research in the field of physics.
Laws have been introduced in Chile and other countries with astronomical observatories to ensure that not more artificial light than necessary is emitted in the vicinity of such facilities.