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.
What if the sky filled up with satellites?
A new form of light pollution, invisible by day but very real at night: low-Earth-orbit satellite constellations (Starlink, OneWeb, Amazon Kuiper…) now streak across astronomers' photographs.
Positions of low-Earth-orbit satellites, recomputed every 5 minutes from public NORAD/Celestrak data.
ESA estimates ~36,500 debris larger than 10 cm in orbit, not counting millions of smaller fragments. Each collision generates more — this is the Kessler syndrome.
Before Starlink: low Earth orbit was still relatively uncrowded.
In five years the orbital population jumped +60%, driven by commercial constellations.
Starlink (42,000), Kuiper (3,236), OneWeb and other approved projects multiply launches.
Sources: Union of Concerned Scientists (2024), ESA Space Debris Office, Celestrak/NORAD.
Why do satellites pollute the sky?
A satellite doesn't shine on its own: it reflects sunlight down to Earth. At dusk and dawn, when the Sun still illuminates low orbit while night has fallen on the ground, thousands of satellites become visible to the naked eye. On a long exposure of a few minutes, each one draws a straight line across astronomers' frames.
Streaks on images
A single 30-second exposure can be crossed by several satellites. On large surveys (Rubin Observatory, 30s per frame), up to 30% of images would be affected at twilight.
Radio-bright satellites
At 10 GHz and above (bands observed by ALMA, SKA…), satellites emit stray radiation that disrupts radio astronomy observations, even when out of the optical field.
Collision risk
More orbiters = higher collision probability. A single collision shatters satellites into thousands of debris, which can in turn hit other craft. This is the Kessler syndrome.
What about data centers?
The rise of AI and data centers accelerates the demand for bandwidth and orbital computing (edge computing, data-relay constellations). More ground centers = more satellite links needed = more launches. Amazon's Kuiper project (3,236 satellites) and Starlink expansions (up to 42,000 units) are symptoms of this.
What can we do?
- •Favor observations in the middle of the night, when low orbit is in Earth's shadow.
- •Support mitigation efforts (darker satellites, occulters, software masking) led by the astronomy community.
- •Make the voice of the night sky heard by regulators (FCC, ITU) for a regulated low orbit.
