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The Bortle scale (also known as the Bottle scale) is a nine-level numeric scale that measures the
* 4673 Bortle
* Amateur astronomy
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Interactive demo of the Bortle Scale International Dark-Sky AssociationObservingSites.com (North American sites only)
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The Bortle scale (also known as the Bottle scale) is a nine-level numeric scale that measures the night sky
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
Natural light sources in a night sky include ...
's brightness
Brightness is an attribute of visual perception in which a source appears to be radiating or reflecting light. In other words, brightness is the perception elicited by the luminance of a visual target. The perception is not linear to luminance, ...
of a particular location. It quantifies the astronomical
Astronomy () is a natural science that studies celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and evolution. Objects of interest include planets, moons, stars, nebulae, galaxies ...
observability of celestial objects
An astronomical object, celestial object, stellar object or heavenly body is a naturally occurring physical entity, association, or structure that exists in the observable universe. In astronomy, the terms ''object'' and ''body'' are often us ...
and the interference caused by light pollution
Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day ...
. John E. Bortle
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 ...
created the scale and published it in the February 2001 edition of ''Sky & Telescope
''Sky & Telescope'' (''S&T'') is a monthly American magazine covering all aspects of amateur astronomy, including the following:
*current events in astronomy and space exploration;
*events in the amateur astronomy community;
*reviews of astronomic ...
'' magazine to help amateur astronomers
Amateur astronomy is a hobby where participants enjoy observing or imaging celestial objects in the sky using the unaided eye, binoculars, or telescopes. Even though scientific research may not be their primary goal, some amateur astronomer ...
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
Naked eye, also called bare eye or unaided eye, is the practice of engaging in visual perception unaided by a magnifying, light-collecting optical instrument, such as a telescope or microscope, or eye protection. Vision corrected to normal ...
limiting magnitude
In astronomy, limiting magnitude is the faintest apparent magnitude of a celestial body that is detectable or detected by a given instrument.
In some cases, limiting magnitude refers to the upper threshold of detection. In more formal uses, limi ...
(NELM). The accuracy and utility of the scale have been questioned in recent research. The table below summarizes Bortle's descriptions of the classes. Some classes can have very drastic differences from the one next to it, e.g, Bortle 4 to 5.
In popular culture
The bandDays N' Daze
Days N' Daze is an American band formed in Houston, Texas performing a type of folk punk they have called 'H-Town Thrashgrass'. Promoting a strong DIY ethic, Days N' Daze independently records, produces, and promotes all their own music. Song the ...
referenced the scale in the title and lyrics of their song ''Nine on the Bortle''.
See also
* 4673 Bortle
* Amateur astronomy
*Dark-sky movement
The dark-sky movement is a campaign to reduce light pollution. The advantages of reducing light pollution include an increased number of stars visible at night, reducing the effects of electric lighting on the environment, improving the well-being, ...
* ''The End of Night'' (book)
* International Dark-Sky Association (IDA)
*Light pollution
Light pollution is the presence of unwanted, inappropriate, or excessive use of artificial Visible spectrum, lighting. In a descriptive sense, the term ''light pollution'' refers to the effects of any poorly implemented lighting, during the day ...
*Night sky
The night sky is the nighttime appearance of celestial objects like stars, planets, and the Moon, which are visible in a clear sky between sunset and sunrise, when the Sun is below the horizon.
Natural light sources in a night sky include ...
*Sky brightness
Sky brightness refers to the visual perception of the sky and how it scatters and diffuses light. The fact that the sky is not completely dark at night is easily visible. If light sources (e.g. the Moon and light pollution) were removed fro ...
*''Sky & Telescope
''Sky & Telescope'' (''S&T'') is a monthly American magazine covering all aspects of amateur astronomy, including the following:
*current events in astronomy and space exploration;
*events in the amateur astronomy community;
*reviews of astronomic ...
'' (''S&T'')
References
External links
* by ''Sky & Telescope
''Sky & Telescope'' (''S&T'') is a monthly American magazine covering all aspects of amateur astronomy, including the following:
*current events in astronomy and space exploration;
*events in the amateur astronomy community;
*reviews of astronomic ...
''Interactive demo of the Bortle Scale
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