Scale for measuring the brightness of the night sky
"Bortle" redirects here. For the asteroid, see 4673 Bortle.
Representation of the Bortle scale
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. Amateur astronomer John E. Bortle created the scale and published it in the February 2001 edition of Sky & Telescope magazine to help skywatchers evaluate the darkness of an observing site, and secondarily, to compare the darkness of observing sites.
The scale ranges from Class 1, the darkest skies available on Earth, through to Class 9, inner-city skies. It gives several criteria for each level beyond naked-eye limiting magnitude (NELM).[1] The accuracy and utility of the scale have been questioned in 2014 research.[2][why?] The table summarizes Bortle's descriptions of the classes. For some classes, there can be drastic differences from one class to the next, e.g, Bortle 4 to 5.[why?]
^Bortle, John E. (February 2001). "Gauging Light Pollution: The Bortle Dark-Sky Scale". Sky & Telescope. Sky Publishing Corporation. Retrieved 2020-05-29.
^Crumey, Andrew (2014). "Human Contrast Threshold and Astronomical Visibility". Monthly Notices of the Royal Astronomical Society. 442 (3): 2600–2619. arXiv:1405.4209. Bibcode:2014MNRAS.442.2600C. doi:10.1093/mnras/stu992.
The Bortle dark-sky scale (usually referred to as simply the Bortlescale) is a nine-level numeric scale that measures the night sky's brightness of a...
entire world. The Bortlescale is a nine-level measuring system used to track how much light pollution there is in the sky. A Bortlescale of four or less...
Australia B-Line bus route Chopin's Ballade No. 1 The darkest sky on the Bortlescale Search for "B1" on Wikipedia. All pages with titles beginning with B1...
beyond the breakers during the summer and fall. At nighttime, the park is BortleScale Class 3, making it a popular stargazing site for those in Eastern Massachusetts...
the observatory. The darkness of the night sky is classified on the Bortlescale from 1 ("excellent", i.e., extremely dark) to 9 ("Inner-city sky", i...
when adapting to darkness. One scientific measure of darkness is the Bortlescale, which indicates the night sky's and stars' brightness at a particular...
new moon, the sky darkness of Joshua Tree is rated a class 2–4 on the Bortlescale. This ranges from an "average dark sky" (class 2) in the easternmost...
dark rural areas located 200 km (120 mi) from major cities. (See the Bortlescale.) There is even variation within metropolitan areas. For those who live...
January 2019. Retrieved 8 November 2018. John E. Bortle (February 2001). "The Bortle Dark-Sky Scale". Sky & Telescope. Archived from the original on 23...
Eta Carinae". NASA. Retrieved 2 August 2018. Bortle, John E. (2001). "Introducing the Bortle Dark-Sky Scale". Sky and Telescope. 101 (2): 126. Bibcode:2001S&T...
only four such reserves around the world at that time. The area has a BortleScale of 2. There are 5 large telescopes on the mountain that are in regular...
the brightest component is barely visible with the unaided eye (see Bortlescale). No planets have yet been detected around any of the stars in this system...
star system in April 2021 was EQ Pegasi (20.4 ly). According to the Bortlescale, an astronomical object is visible to the naked eye under "typical" dark-sky...
than 21.3 mag/arcsec2 (corresponding to Bortlescale 3), and in places are as dark as 21.8 mag/arcsec2 (Bortlescale 1). Large parts of the Wairarapa region...
catalogue as "XVI 55". With an apparent magnitude of 5.38, according to the Bortlescale it is visible to the naked eye from suburban skies. Based upon stellar...
lease arrangement with the U.S. Army Corps of Engineers. The park has Bortlescale class 1 skies (low light pollution). "Hell Creek State Park". Geographic...
45 mag/arcsec2 (corresponding to Bortlescale 3), and in places are as dark as 21.76 and 21.80 mag/arcsec2 (Bortlescale 1). The application for designation...
1995 with unemployed PhD physicist Alan Hale. John E. Bortle, best known for creating the Bortlescale to quantify the darkness of the night sky. Robert Burnham...
to be viewed from the Earth with the unaided eye. (According to the Bortlescale, it can be viewed from dark suburban skies.) HD 192310 is suspected of...
does not mention any variable-star type for the star. According to the Bortlescale The distance in parsecs is equivalent to ( 1 parallax ) {\displaystyle...
Astronomy Week Noctcaelador White House Astronomy Night Light pollution Bortlescale "Home". "What Is National Dark Sky Week?". Wise Geek. Conjecture Corporation...
constellation of Aquila. With an apparent magnitude of 6.14, according to the Bortlescale it is faintly visible to the naked eye from rural skies on a dark night...
Borrmann–Campbell effect) – Gerhard Borrman (and Herbert N. Campbell) Bortlescale – John E. Bortle Bose–Einstein condensate, effect, statistics – Satyendra Nath...
stargazing program once a month from April through October. The park's BortleScale rating is a Class 2, which indicates there's a very low amount of light...
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