Astronomers rely on minimal light pollution to observe faint stars, planets, and nebulae. The Bortle scale ranks night skies from 1 (excellent dark sky) to 9 (inner-city glow). Distance from urban areas and atmospheric clarity also influence visibility. This tool gives you a simple score to judge your stargazing prospects. The underlying MathML formula is:
where is the Bortle class, is distance from the nearest major city in kilometers, and represents a clarity factor between zero and one. Higher scores indicate better stargazing conditions.
Driving far from city lights often yields darker skies, yet humidity, dust, or wildfire smoke can still obscure faint objects. Use the clarity factor to account for local weather or seasonal haze. Even a perfect Bortle 1 site won’t provide good views if the air is murky.
| Bortle | Distance (km) | Clarity | Score |
|---|---|---|---|
| 3 | 20 | 0.8 | 112 |
| 5 | 5 | 0.6 | 30 |
These values show how traveling farther and finding crystal-clear conditions dramatically improves your ability to see the Milky Way or meteor showers.
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