July 29, 2021 5.12pm

Globally, nights are becoming ever brighter. Increasing urbanisation and the installation of new streetlights, security floodlights and outdoor ornamental lighting all contribute to growing light pollution.

This light floods directly into the eyes of animals that are active at night and also into the skies. There a proportion of it is redirected back downwards towards an earthbound observer. This is known as “skyglow”, an omnipresent sheet of light across the night sky in and around cities that can block all but the very brightest stars from view.

We wanted to understand how this change in night brightness would affect animals that rely on the sky as their compass. Would their sensitive eyes be blinded by bright city lights? Would the disappearance of stars from the night sky cause them to lose their way? So we used the well-studied “sky compass” of the nocturnal dung beetle, Scarabaeus satyrus, to compare orientation under pristine and light polluted skies.

Our study compared the dung-rolling performance of beetles in a rural part of Limpopo province with that of beetles at the University of Witwatersrand in inner city Johannesburg, both in South Africa. Our findings confirm that beetles exposed to light pollution – both directly through the glare of bright artificial lights and indirectly via skyglow that obscures the stars – are forced to change strategy. They abandon their sky compass and rely instead on earthbound artificial lights as beacons.

This change in strategy comes at a cost.

Read more at https://theconversation.com/skyglow-forces-dung-beetles-in-the-city-to-abandon-the-milky-way-as-their-compass-165110

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Abstract

The US National Park Service (NPS) Night Skies Program measured changes in sky brightness resulting from a countywide lighting retrofit project. The retrofit took place in Chelan County, a gateway community to North Cascades National Park and Lake Chelan National Recreation Area in Washington State. The county retrofitted all 3693 county-owned high pressure sodium (HPS) street lamps to full cutoff LEDs. This number is about 60% of the County’s total outdoor street and area lights. About 80% of the newly installed lights were 3000 K in color temperature and 20% were 4000 K. The 4000 K LEDs were used to meet Washington State Department of Transportation guidelines. To measure sky brightness, we used the NPS night sky camera system before the retrofit started in 2018 and after its completion in 2019. These images were photometrically calibrated and mosaicked together to provide hemispherical images in V band. For comparison with our ground-based measurement, we obtained the satellite imagery taken by Visible Infrared Imaging Radiometer Suite (VIIRS) onboard the Suomi National Polar-orbiting Partnership satellite. Our measurements show that the post-retrofit skyglow became brighter and extended higher in the sky, but upward radiance, as measured by the day-night band radiometer, decreased. These divergent results are likely explained by a substantial increase in light emitted at wavelengths shorter than 500 nm, and a relative decrease in upward light emission due to better shielded luminaires. These results also demonstrate that earlier models relating VIIRS day-night band data to skyglow will – at a minimum – require substantial revision to account for the different characteristics of solid state luminaires.

Extract

The authors:

How do we convert to LED technology in a way that reduces energy consumption, reduces skyglow, preserves historical ambiance, and still meets the safety and security needs of our communities?

We believe with proper design and usage, energy savings and light pollution reductions can stand on the same side, both benefiting from LED retrofits. This study implies reductions in skyglow will require lowering overall light level (>50%), using warmer lights (< 3000 K), or both. Perceived conflicts between streetlighting objectives and light pollution can be further mitigated through controls that dim lights during periods of low traffic. More case studies are needed to pinpoint the exact criteria for a lighting retrofit to reduce skyglow. Nonetheless, a strong proactive lighting design is the key to converting to LED lights without increasing light pollution.

https://www.sciencedirect.com/science/article/pii/S0301479721008380

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Abstract

The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite ‘mega-constellations’ in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 μcd m⁻², which amounts to an approximately 10 percent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories.

© The Author(s) 2021. Published by Oxford University Press on behalf of The Royal Astronomical Society.

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Abstract

We conduct the first study to examine the fetal health impact of light pollution based on a direct measure of skyglow, an important aspect of light pollution. Using an empirical regularity discovered in physics (called Walker’s law) as an instrumental variable, we address the potential endogeneity problem associated with the skyglow variable. We find evidence of reduced birth weight, shortened gestational length, and increases in preterm births. Specifically, increased nighttime brightness, characterized by being able to see only one‐fourth to one‐third of the stars that are visible in the natural unpolluted night sky, is associated with an increase of 1.48 percentage points in the likelihood of a preterm birth. Our study adds to the literature on the impact of early‐life exposure to pollution, which so far has focused primarily on air pollution. Our study has important policy implications regarding the necessity of minimizing skyglow that is, for example, contributed by streetlights.

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