A vocabulary of landscape — a landscape of words
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Bortle scale
A nine-level numeric scale for measuring the darkness of a night sky, from Class 1 (the darkest sky attainable on earth — zodiacal light visible, the Milky Way casting shadows) to Class 9 (inner-city sky — only the Moon, planets, and a few bright stars visible).
Etymology
Created by amateur astronomer John Bortle and published in Sky & Telescope magazine in 2001. Named for its author.
Notes
The Bortle scale belongs alongside the Beaufort scale and the Mercalli scale — human-observation measurement systems that describe the world not with instruments but with what you can see and feel.