How to read the dark-sky map

The color ramp

The map colors every spot by measured sky brightness, from dark purple (darkest) to yellow (brightest). Darker on screen means a darker sky. The ramp is Viridis, chosen because it stays readable if you're colorblind.

Six named bands sit along that ramp:

• Very dark sky — up to 0.25 nW/cm²/sr
• Dark sky — up to 1 nW/cm²/sr
• Rural — up to 3 nW/cm²/sr
• Suburban — up to 10 nW/cm²/sr
• Bright suburban / urban fringe — up to 30 nW/cm²/sr
• Urban / heavily light-polluted — above 30 nW/cm²/sr

These are approximate radiance bands, not a Bortle or SQM class.

Setting a start point and reading the panel

Set a start point on the map first — usually where you live. Then click any spot you're considering. A panel opens with:

• Darkness band — which of the six bands that spot falls in.
• Distance — the straight-line distance from your start point, in kilometers.
• Approximate drive — that distance divided by a flat 70 km/h. Not a routed estimate; check a real map before you drive.
• Forecast — the short-range cloud outlook for the next few nights.
• Moon window — the part of the night when the moon is down or dim enough not to wash out a dark sky.

What each reading means, and what it doesn't promise

The darkness band is a yearly satellite average, not a live reading — it won't show a streetlight that switched on last week. The distance and drive figures ignore roads and traffic; they're a rough guide, not directions. Nothing on the map is a guarantee of clear skies — check the forecast panel for that spot before you go.

Where the data comes from

• Darkness — VIIRS/VNL upward radiance, a 2025 annual satellite composite from the Earth Observation Group at the Colorado School of Mines (CC BY 4.0).
• Cloud forecast — MET Norway (CC BY 4.0).
• Map tiles — OpenFreeMap, OpenMapTiles, and OpenStreetMap data.
• Sun and moon positions — Astronomy Engine by Don Cross (MIT license).

Next steps

Open the map and try setting a start point near you. If you're trying to work out how far you need to go, see how far to a dark sky. For an overview of what the product is and isn't, see what Star Ninja is.