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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 .
In order to describe how much light pollution there is at a particular location, astronomers classify night skies based on the Bortle Scale.
Location Area (in ha) Bortle Scale Status Notes Australia: The Jump-Up, Australian Age of Dinosaurs: Queensland: 1,400 1–2 Dark Sky Sanctuary Designated on April 27, 2019 Australia: Warrumbungle National Park: New South Wales: 23,312 1 Dark Sky Park Designated on July 4, 2016 Australia: Arkaroola Wilderness Sanctuary: South Australia: 63,000
On clear nights around new moon, the sky darkness of Joshua Tree is rated a class 2–4 on the Bortle scale. [51] [52] This ranges from an "average dark sky" (class 2) in the easternmost region of the park to a sky quality typical of a rural/suburban transition (class 4) in the western regions near Palm Springs.
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.
The park has an astronomical observatory. The observatory site is located in a region rated 5 on the Bortle scale (i.e. the brightness scale of the night sky). This situation favors the observation of the sky because the site is surrounded by agricultural land.
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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