BORTLE SCALE

The Bortle Scale is a nine-level numeric measure of the night sky’s brightness in a particular location. It quantifies the astronomical visibility of celestial objects and the interference caused by light pollution. John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help amateur astronomers evaluate and compare the darkness of observing sites. The scale ranges from Class 1, the darkest skies available on Earth, to Class 9, daylight-like inner city skies.

Do you know where your night sky ranks on the Bortle Scale?

Image Credit: SKYGLOW
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