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Earth's sky is never completely black – even in the absence of light pollution there is a natural airglow that limits what can be seen. The astronomer H.D. Curtis reported his naked-eye limit as 6.53, but by looking at stars through a hole in a black screen (i.e. against a totally dark background) was able to see one of magnitude 8.3, and ...
the sky is light gray or orange – one can easily read; stars forming familiar constellation patterns may be weak or invisible; M31 and M44 are barely glimpsed by an experienced observer on good nights; even with a telescope, only bright Messier objects can be detected; limiting magnitude with 12.5" reflector is 13; 9 Inner-city sky 4.0
Amateur astronomers commonly express the darkness of the sky in terms of limiting magnitude, i.e. the apparent magnitude of the faintest star they can see with the naked eye. This can be useful as a way of monitoring the spread of light pollution. Apparent magnitude is technically a measure of illuminance, which can also be measured in ...
Light pollution is the presence of any unwanted, inappropriate, or excessive artificial lighting. [1] [2] In a descriptive sense, the term light pollution refers to the effects of any poorly implemented lighting sources, during the day or night. Light pollution can be understood not only as a phenomenon resulting from a specific source or kind ...
More than 99% of Americans live under skies polluted by light. But dark skies at the Grand Canyon and more than 145 other spots offer stargazing awe.
Data showed that Earth's artificially lit outdoor surface at night grew by about 2 percent annually in brightness and area from 2012 to 2016.
Light pollution is an ever-increasing source of sky brightness in urbanized areas. In densely populated areas that do not have stringent light pollution control, the entire night sky is regularly 5 to 50 times brighter than it would be if all lights were switched off, and very often the influence of light pollution is far greater than natural ...
With the advent of artificial light sources, however, light pollution has been a growing problem for viewing the night sky. Special filters and modifications to light fixtures can help to alleviate this problem, but for the best views, both professional and amateur optical astronomers seek viewing sites located far from major urban areas.