Night Sky Quality Monitoring Report
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Hopewell Furnace NHS |
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Meadow south of Church House |
16-Aug-2014 |
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To effectively manage any resource, we need to know what we have and what we've lost. Light pollution, the brightness in the nighttime sky due to artificial light, effectively masks natural sources of light at night such as the stars and the Milky Way. The NPS has developed a system for measuring sky brightness to quantify the source and severity of light pollution. This system, developed with assistance from professional astronomers and the International Dark‐Sky Association, uses a research‐grade digital camera to capture the entire sky with a series of images. Data clearly show that almost every park, even remote national parks, are not immune from stray artificial light. Sky brightness is measured in astronomical magnitudes in the visual band or V‐band, abbreviated as "mags". The V‐band measures mostly green light, omitting purple through ultraviolet and orange through infrared. The magnitude scale is a logarithmic scale. A difference of 5 magnitudes corresponds to a 100x difference in brightness. Lower values (smaller or more negative) are brighter. Further information on astronomical magnitudes can be found on this Sky and Telescope webpage. Data images are shown in false color, with yellow, red, and white corresponding to brighter sky and blue, purple and black corresponding to darker sky.
A more detailed explanation is available.
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Data Set Attributes and Visual Indicators
Photometric Indicators
Observed |
Estimated Artificial |
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Sky Luminance Measures |
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mag/ arscec2 |
μcd/ m2 |
mag/ arscec2 |
μcd/ m2 |
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Zenith |
20.23 |
876 |
20.45 |
707 |
4.13 |
Mean all-sky |
19.04 |
2,629 |
19.13 |
2,388 |
9.62 |
Brightest |
16.84 |
19,727 |
16.85 |
19,538 |
114.26 |
Darkest |
20.22 |
871 |
20.44 |
711 |
4.16 |
Median |
19.42 |
1,832 |
19.57 |
1,585 |
6.34 |
Illuminance Measures |
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mags |
milli-lux |
mags |
milli-lux |
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Horizontal |
-8.37 |
5.64 |
-8.22 |
4.90 |
6.13 |
Max Vertical |
-8.44 |
6.03 |
-8.35 |
5.55 |
13.88 |