Skyglow

Part of this artificial light at night interacts with the air molecules and aerosols, and it is absorbed and scattered depending on the optical characteristics of the surrounding environment (see § Mechanism) thus creating skyglow.[9] All-sky maps of skyglow brightness are produced with professional-grade imaging cameras with CCD detectors and using stars as calibration sources.[10][11] Amateur astronomers have used the Bortle Dark-Sky Scale to approximately quantify skyglow ever since it was published in Sky & Telescope magazine in February 2001.Amateurs also increasingly use Sky Quality Meters (SQM) that nominally measure in astronomical photometric units of visual (Johnson V) magnitudes per square arcsecond.But the basic results of recent research are unambiguous: assuming equal luminous flux (that is, equal amounts of visible light), and matched optical characteristics of the fixtures (particularly the amount of light allowed to radiate directly upward), white sources rich in shorter (blue and green) wavelengths produce dramatically greater sky glow than sources with little blue and green.[26] Close to global coastal megacities (e.g. Tokyo, Shanghai), the natural illumination cycles provided by the moon in the marine environment are considerably disrupted by light pollution, with only nights around the full moon providing greater radiances, and over a given month lunar dosages may be a factor of 6 less than light pollution dosage.[27] Due to skyglow, people who live in or near urban areas see thousands fewer stars than in an unpolluted sky, and commonly cannot see the Milky Way.[30] As a whole, these effects derive from changes in orientation, disorientation, or misorientation, and attraction or repulsion from the altered light environment, which in turn may affect foraging, predator-prey dynamics,[31][32] reproduction,[33] migration, and communication.In turn, the effects of sky glow can affect production rates of agriculture, especially in farming areas that are close to large city centers.
Mexico City at night, showing skyglow
A map from 1996 to 1997 showing the extent of skyglow over Europe
In this 10-second exposure, facing south toward Sagittarius , three forms of light pollution are present: skyglow, glare , and light trespass .
In remote areas on moonless nights clouds appear dark against the sky. In or near developed areas skyglow is strongly enhanced by clouds.
A calibrated all-sky map in the vicinity of Ashurst Lake , Arizona , showing skyglow brightness, including artificial ( Phoenix and Flagstaff, Arizona ) and natural sources ( airglow , Milky Way) are visible (U.S. National Park Service).
Skyglow brightness ratio (compared to low-pressure sodium) vs. distance for various lamp types. [ 8 ]
Skyglow is mostly unpolarized, and its addition to moonlight results in a decreased polarization signal. Humans cannot perceive this pattern , but some arthropods can.
airglowzodiacal lightlight pollutionMexico Cityluminancenight skylightingscattered lightstarlightgas flaresatmospherescattered backdiffuse glowdeveloped worldSagittariuscloudsRayleigh scatteringaerosolsMie theoryextinctionBortle Dark-Sky ScaleSky Quality MetersJohnsonAshurst LakeArizonaPhoenixFlagstaff, Arizonainverse square lawPurkinje shiftscotopicphotopicmetal halidefluorescenthigh-pressure sodiumAluminium gallium indium phosphideluminous fluxInternational Dark-Sky Associationpatternarthropodsastronomerscontrastbrightest starspolarizationsignalscattered moonlightMilky WayAndromeda GalaxyEcological light pollutionurbanizationcommercializationconsumerismmigratory birdsphotosynthesisSKYGLOWPolarized light pollutionOver-illuminationDark-sky movementCampaign for Dark Skieslow-pressure sodiumemissionRoach, Franklin E.DordrechtSky & TelescopeBibcodeMonthly Notices of the Royal Astronomical Societycameras