How to use this tool
1. Adjust Visibility: Use the Pollution Opacity slider to blend the artificial light layer with the base map.
2. Change Map Style: Select different base maps (e.g., Dark for contrast, Satellite for geography) from the left panel.
3. Data: Standard national borders are loaded automatically for reference (white lines).
4. Check a location: Click any point on the map to see how much artificial light brightens the sky there and what that means for stargazing.
How to read the light pollution colors
Every color is a level of artificial sky brightness at the zenith, expressed as a share of the natural night-sky brightness. Each step doubles the one before it.
| Color | Artificial light vs. natural sky | What it means |
|---|---|---|
| Black | under 1% | Essentially pristine sky |
| Dark gray | 1–2% | Threshold at which a site is considered worth protecting |
| Gray | 2–4% | Slight artificial glow |
| Dark blue | 4–8% | Glow visible toward towns on the horizon |
| Blue | 8–16% | Polluted by the astronomers' (IAU) definition |
| Light blue | 16–32% | Clearly polluted rural sky |
| Dark green | 32–64% | Bright rural or outer suburban sky |
| Green | 64–128% | Artificial light about equal to the natural sky |
| Yellow | 1.3–2.6× | Winter Milky Way no longer visible |
| Orange | 2.6–5× | Summer Milky Way hidden as well |
| Red | 5–10× | Eyes can no longer fully adapt to darkness |
| Magenta | 10–20× | Bright urban sky |
| Pink | 20–40× | Very bright urban sky |
| White | over 40× | City-center sky; only the brightest stars show |
Natural sky brightness here means a clean, moonless sky of about 22 magnitudes per square arcsecond.
Where does the data come from?
The light layer follows the New World Atlas of Artificial Night Sky Brightness (Falchi et al., Science Advances, 2016). The authors combined night-time satellite radiance with a model of how light scatters in the atmosphere, then calibrated the result against ground measurements of sky brightness. The grid is roughly one kilometer, which is why the map turns blocky at street level.
Light pollution maps and the Bortle scale
The Bortle scale rates a site from 1 (excellent dark sky) to 9 (inner-city sky) by what an observer can see. This atlas instead models measured brightness, so the two do not line up class for class. As a rough guide, black and dark gray areas are where Bortle 1–2 skies are found, and yellow-to-white areas are where the Milky Way has disappeared, typical of Bortle 6 and above.
Frequently asked questions
Why does the map look blocky when I zoom in?
The sky-brightness data has a resolution of roughly one kilometer. Zooming in further enlarges the same cells; it does not add street-level detail.
Is the light pollution map up to date?
The atlas is modeled from satellite measurements taken in the mid-2010s. Many places have changed lighting since then, especially with the switch to white LEDs, so use it as a baseline rather than tonight's conditions.
How do I find a dark-sky place near me?
Search for your city, then look outward for black, gray or dark-blue areas within driving distance. Click a spot to confirm its level, and switch to Satellite or Terrain to check whether it is reachable.