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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.
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.
The nine chapters of Bogard's book map to the nine levels of the Bortle scale, which attempts to quantify the subjective brightness and suitability for astronomy of the sky in different environments. Bogard has said of the scale, invented in 2001, "one of the reasons why identifying different depths of darkness is so important is that we don't ...
The darkness of the night sky is classified on the Bortle scale from 1 ("excellent", i.e., extremely dark) to 9 ("inner-city sky", i.e., partially dark). Hanle is categorised as an excellent dark astronomical site with Bortle colour key "Black". [9] The dark sky is important for the conservation of nocturnal animals and ecology.
According to the Bortle scale, it is faintly visible to the naked eye from dark rural skies. The star is located at a distance of approximately 970 light years from the Sun based on parallax , [ 8 ] but is drifting closer with a radial velocity of −7 km/s.
This system has an apparent visual magnitude of 5.1, [2] which, according to the Bortle scale, makes it faintly visible to the naked eye from suburban skies. Measurements made with the Hipparcos spacecraft show an annual parallax shift of 0.064″, [ 1 ] corresponding to a physical distance of about 51.0 ly (15.6 pc) from the Sun.
[10] [12] Despite this, even the brightest component is barely visible with the unaided eye (see Bortle scale). No planets have yet been detected around any of the stars in this system. This is a triple system with three stars that are all less massive than the Sun. The brightest component is designated HD 16160, and is known as Gliese 105 A.