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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 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.
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.
HR 6594 is the Bright Star Catalogue designation for a binary star [12] system in the northern constellation of Hercules.It is faintly visible to the naked eye with an apparent visual magnitude of 5.54; [2] according to the Bortle scale, it is sufficiently bright to be visible from dark suburban skies.
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.
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HD 35984 is star in the northern constellation Auriga.It has an apparent magnitude of 6.20, [2] which, according to the Bortle scale, indicates it is faintly visible to the naked eye from dark rural skies.