Observing / Light pollution
Light pollution map
An interactive light pollution map. Find dark-sky areas by Bortle scale around your location, then open the map in fullscreen.
Light pollution & the Bortle scale
The Bortle scale measures night-sky quality on a scale of 1 (pristine dark sky) to 9 (city center). The lower the number, the more stars, galaxies and nebulae you will see. Light pollution from cities hides the Milky Way and drastically reduces the number of visible objects.
How does it work?
Our Bortle class estimate reads directly from 2024 VIIRS satellite data (D. J. Lorenz's Light Pollution Atlas) at your GPS location — the same data shown on our light pollution map. The actual artificial sky brightness at your coordinates is converted to a Bortle class (1 = pristine dark sky, 9 = city center).
Why does it matter?
Light pollution doesn't just bother astronomers: it disrupts nocturnal wildlife (migratory birds, pollinating insects, bats) and affects human sleep. In France, 85% of the population can no longer see the Milky Way from where they live.
How can things improve?
If your sky is light-polluted, travel at least 20-30 km from large cities. Use light pollution maps like lightpollutionmap.info to find dark areas. Favor moonless nights (new moon) and set up away from direct streetlights.