Abstract
Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program.
Highlights
Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited
Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by,25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models
Seasonal, and lunar cycles of light that had previously been rather invariant for millennia have been dramatically altered by the spread of both public and private nighttime lighting, much of it associated with the global network of,18 million kilometers of paved roads[1]
Summary
Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. The invention of robust and easy to use light meters like the ‘‘Sky Quality Meter’’ (SQM; Unihedron), has resulted in a boom in skyglow measurement[29,30,31,32,33,34,35,36,37,38,39,40] This has led to some understanding of patterns on a local scale, and emphasized the need for comparative studies across different regions. For the first time we bring together data obtained from SQMs at 44 sites around the globe to address four key questions about skyglow: 1) what levels of sky radiance are currently experienced worldwide, and how do these compare to the levels experienced under celestial light only?
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