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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 .
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.
A dark-sky preserve status enables high-quality astronomical observation in Paranal Observatory. [1]A dark-sky preserve (DSP) is an area, usually surrounding a park or observatory, that restricts or reduces light pollution or maintains and protects naturally dark night skies.
The limiting magnitude for naked eye visibility refers to the faintest stars that can be seen with the unaided eye near the zenith on clear moonless nights. The quantity is most often used as an overall indicator of sky brightness, in that light polluted and humid areas generally have brighter limiting magnitudes than remote desert or high altitude areas.
The modern scale was mathematically defined to closely match this historical system by Norman Pogson in 1856. The scale is reverse logarithmic: the brighter an object is, the lower its magnitude number. A difference of 1.0 in magnitude corresponds to the brightness ratio of , or about 2.512. For example, a magnitude 2.0 star is 2.512 times as ...
This scale is widely referred to by various names, including very commonly "Bortle scale". A large number of the instances of "Bortle Dark-Sky Scale" in books are references to Bortle's paper title "Introducing the Bortle Dark-Sky Scale", which is usually but not always capitalized.
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 .
Location: West Branch, Potter, Pennsylvania, United States: Coordinates: 1]: Area: 82 acres (33 ha): Elevation: 2,300 ft (700 m) [1]: Established: 1922 [2]: Named for: A large stand of cherry trees in the park: Visitors: 52,229 [3]: Governing body: Pennsylvania Department of Conservation and Natural Resources: Website: Cherry Springs State Park: Cherry Springs State Park is an 82-acre (33 ha ...