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The Bortle dark-sky scale (usually referred to as simply the Bortle scale) is a nine-level numeric scale that measures the night sky's brightness of a particular location. It quantifies the astronomical observability of celestial objects and the interference caused by light pollution .
The park is well known for its naturally dark night skies, which are far away from and largely free of the light pollution typical in urban areas. In 2017, the International Dark-Sky Association designated Joshua Tree a Dark Sky Park. [50] On clear nights around new moon, the sky darkness of Joshua Tree is rated a class 2–4 on the Bortle scale.
The Bortle scale is a nine-level measuring system used to track how much light pollution there is in the sky. A Bortle scale of four or less is required to see the Milky Way whilst one is "pristine", the darkest possible.
In order to describe how much light pollution there is at a particular location, astronomers classify night skies based on the Bortle Scale.
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John E. Bortle is an American amateur astronomer. He is best known for creating the Bortle scale to quantify the darkness of the night sky. Bortle has made a special study of comets. He has recorded thousands of observations relating to more than 300 comets. From 1977 until 1994 he authored the monthly '"Comet Digest" in Sky and Telescope magazine.
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All measurements of night sky luminance in the core area are darker than 21.3 mag/arcsec 2 (corresponding to Bortle scale 3), and in places are as dark as 21.8 mag/arcsec 2 (Bortle scale 1). Large parts of the Wairarapa region outside the core of the reserve exceed the minimum value of 21.2 mag/arcsec 2 required for the core.