Bortle Scale Map
An interactive Bortle map showing real-time sky darkness — check the Bortle scale for any location on Earth.
Bortle Scale Map (VIIRS satellite data · Classic)
Bortle Scale Map FAQ
New to the Bortle scale map? Here's what you need to know.
What is it
What is the Bortle scale?
The Bortle scale (formally the Bortle dark sky scale) is a 9-level scale created by astronomer John Bortle in 2001 to rate how dark or light-polluted the night sky is at a location, from Class 1 (pristine) to Class 9 (inner-city).
What does each Bortle class mean?
Class 1–2 are excellent dark-sky sites where the Milky Way casts shadows; Class 4–6 are suburban skies where only bright stars are visible; Class 7–9 are urban skies where light pollution hides most of the night sky.
How it works
How do I use this Bortle scale map?
Zoom or search any address on the bortle map — the color overlay shows the estimated Bortle class for that spot based on satellite light pollution data.
How does this Bortle scale map actually work?
The map starts from NOAA's VIIRS satellite data, which measures artificial light radiance from space. A simplified logarithmic formula converts that radiance into an SQM-like brightness value, and the Bortle class shown is a simplified reference derived from that modeled value — not a live field measurement or a full atmospheric model like the professional World Atlas.
Is this Bortle map accurate?
It's a modeled estimate, not a precise scientific measurement — real sky conditions also depend on clouds, moonlight, and local terrain. SQM is the more precise comparison value, and Bortle class here is best used as a quick, easy-to-read reference for planning, not a guarantee of what you'll see.
What's the difference between Bortle scale and SQM?
SQM (Sky Quality Meter) gives a modeled brightness reading in mag/arcsec², while the bortle dark sky scale groups that value into 9 simple categories — this map converts the modeled SQM value into a Bortle class for easy reading.
Who it's for
What Bortle class do I need for stargazing or astrophotography?
Class 1–4 is ideal for viewing faint deep-sky objects and the Milky Way; Class 5–6 still works well for planets, the Moon, and bright astrophotography targets.
Who uses this map?
Amateur astronomers planning an observing trip, astrophotographers scouting dark-sky locations, and travelers or campers who want to know if they'll see the Milky Way at their destination all use this bortle map before heading out.
Where can I find dark sky locations near me?
Use the bortle map to scan outward from your location for the nearest low-Bortle-class (dark sky) areas — parks and rural regions typically offer the biggest improvement.
