Light Pollution Map (Pennsylvania)
There are no dark sky regions (Bortle 1, or B1), in my region of the world. The only dark areas (Bortle 2) are in the north central part of the state located in the undeveloped forest Appalachian Plateau province. Cherry Springs State Park, one of the world's first official dark sites, is located there. And these areas are under threat from new development, especially natural gas sites and homes.
The map below shows the quality of the night skies in Pennsylvania and surrounding areas in Ohio, West Virginia, Maryland and New York. The Milky Way is not visible to the naked eye in vast areas surrounding the cities of Philadelphia, PA, Baltimore, Washington D.C., and New York, NY along the Atlantic coastline. The same holds true for cities areas to the west and near the Great Lakes, including Pittsburgh and Erie, PA and Warren/Youngstown and Cleveland, OH. These metropolitan areas are B6 (orange), B7 (red), B8 (pink) or B9 (white) zones. Even smaller cities, such as Harrisburg, Lancaster, York, Allentown, Scranton, Williamsport and Erie, appear as pockmarks of B6 (yellow), B7 (red) and B9 (pink) as well. Most of Pennsylvania is Bortle 5 (yellow) and Bottle 4 (green), which for imaging requires long exposures, dual band filters for one-shot color cameras, or narrow band filters such as Hydrogen alpha - Oxygen III and Sulfur.
Sky Brightness Scale (at zenith)
The column labeled "Naked-eye Limiting Magnitude" indicates the dimmest stars visible under each class of light pollution. The larger the magnitude number is, the dimmer the star is. Each whole number represents a factor of 2.51 in brightness. In other words, a magnitude 5 star appears approximately two and one-half times brighter than a magnitude 6 star, while a magnitude 4 star appears approximately five times brighter than a magnitude 6 star.
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Map Color
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Artificial / Natural
Sky Brightness
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Sky Brightness
(mag / sq arcsec
visible spectrum)
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Bortle Scale
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Description
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Black
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< 0.01
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22.00 to 21.99
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1
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Theoretically darkest sky limited by airglow and starlight
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|
Dark Gray
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0.01 to 0.06
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21.99 to 21.93
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2
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Gegenschein visible. Zodiacal light annoyingly bright. Rising milkyway confuses some into thinking it's dawn. Limiting magnitude 7.6 to 8.0 for people with exceptional vision. Users of large dobsonian telescopes are very happy.
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Bright Gray
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0.06 to 0.11
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21.93 to 21.89
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2
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Faint shadows cast by milkyway visible on white objects. Clouds are black holes in the sky. No light domes. The milky way has faint extentions making it 50 degrees thick. Limiting magntiude 7.1 to 7.5. [-ad]
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Dark Blue
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0.11 to 0.19
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21.89 to 21.81
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3
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|
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Bright Blue
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0.19 to 0.33
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21.81 to 21.69
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3
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The sky is crowded with stars, extending to the horizon in all directions. In the absence of haze the M.W. can be seen to the horizon. Clouds appear as black silhouettes against the sky. Stars look large and close. [-Richard Berry] Low light domes (10 to 15 degrees) on horizon. M33 easy with averted vision. M15 is naked eye. Milky way shows bulge into Ophiuchus. Limiting magnitude 6.6 to 7.0. [-ad]
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Dark Green
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0.33 to 0.58
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21.69 to 21.51
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4
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21.6: ... a glow in the direction of one or more cities is seen on the horizon. Clouds are bright near the city glow. [-Richard Berry]
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Bright Green
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0.58 to 1.00
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21.51 to 21.25
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4
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Zodiacal light seen on best nights. Milkyway shows much dark lane structure with beginnings of faint bulge into Ophiuchus. M33 difficult even when above 50 degrees. Limiting magnitude about 6.2 to 6.5. [-ad]
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Dark Yellow
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1.00 to 1.73
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21.25 to 20.91
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4.5
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21.1: The M.W. is brilliant overhead but cannot be seen near the horizon. Clouds have a greyish glow at the zenith and appear bright in the direction of one or more prominent city glows. [-Richard Berry] Some dark lanes in milkyway but no bulge into Ophiuchus. Washed out milkyway visible near horizon. Zodiacal light very rare. Light domes up to 45 degrees. Limiting magnitude about 5.9 to 6.2. [-ad]
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Bright Yellow
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1.73 to 3.00
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20.91 to 20.49
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4.5
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|
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Dark Orange
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3.00 to 5.20
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20.02 to 19.50
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5
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20.4: To a city dweller the M.W. is magnificent, but contrast is markedly reduced, and delicate detail is lost. Limiting magnitude is noticeably reduced. Clouds are bright against the zenith sky. Stars no longer appear large and near. [-Richard Berry] Milkyway washed out at zenith and invisible at horizon. Many light domes. Clouds are brighter than sky. M31 easily visible. Limiting magnitude about 5.6 to 5.9.[-ad]
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Bright Orange
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5.20 to 9.00
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20.91 to 20.49
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5
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|
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Dark Red
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9.00 to 15.59
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19.50 to 18.95
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6
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19.5: M.W. is marginally visible, and only near the zenith. Sky is bright and discoloured near the horizon in the direction of cities. The sky looks dull grey. [-Richard Berry] Milkyway at best very faint at zenith. M31 difficult and indestinct. Sky is grey up to 35 degrees. Limiting magntidue 5.0 to 5.5. [-ad]
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Bright Red
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15.59 to 27.00
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18.95 to 18.38
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7
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|
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Bright Grey
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27.0 to 46.77
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18.38 to 17.80
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8
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Entire sky is grayish or brighter. Familliar constellations are missing stars. Fainter constellations are absent. Less than 20 stars visible over 30 degrees elevation in brigher areas. Limiting magntude from 3 to 4.CCD imaging is still possible. But telescopic visual observation is usually limited to the moon, planets, double stars and variable stars. [-ad]
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Off White
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>46.77
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>17.80
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9
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18.5: Stars are weak and washed out, and reduced to a few hundred. The sky is bright and discoloured everywhere. [-Richard Berry] Most people don't look up.[-ad]
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The International Dark-Sky Association: Light Pollution
The International Dark-Sky Association is a non-profit organisation committed to preserving and protecting the night-time environment and shared heritage of dark skies. Their website provides a wide array of information to grow your understanding of the causes and effects of light pollution, with themes specific to wildlife and ecosystems, energy waste, human health, and the intersection of lighting, crime, and safety. Their resources also include videos, infographics, and a research library.
The New World Atlas of Artificial Night Sky Brightness
This resource presents a modern world atlas of global luminance. The content presented here will help you to better visualize and understand the extent to which light pollution is a global issue.
Global Light Pollution Map
This interactive light pollution map provides an array of overlay options that will help you to see the trends in light pollution over the past decade.
