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The Dark Sky Movement
It takes a village to save our night sky
Every astronomer understands the importance of having pristine, dark skies to observe celestial wonders. Unfortunately, light pollution has become a significant issue, affecting more than half of the United States. Not only does it hinder our ability to observe the night sky, but it also negatively impacts human health, wildlife, and the climate.
Human Health
Artificial lighting disrupts our natural circadian rhythm, leading to reduced melatonin production. This reduction can negatively impact sleep, the immune system, and overall organ function. Insufficient melatonin levels can also result in serious issues such as mood disorders, heart disease, and even cancer. A notable study by Thapan, Arendt, and Skene (2001) found that exposure to blue light, specifically, decreases melatonin production. Based on these findings, advocates from DarkSky emphasize the importance of using warm-colored lighting during nighttime to support healthy sleep patterns.
Left: The black squares represent the baseline of a typical night. When exposed to light at wavelengths of 424 nm and 472 nm (white square and circle, respectively), melatonin production decreased. Right: The relationship between shorter wavelengths (higher energy) and melatonin suppression. Credit: Thapan, Arendt, and Skene
Wildlife
Wildlife relies on Earth's natural day/night cycle for essential survival activities such as hunting, sleeping, and breeding. For example, frogs croak at night to attract mates, baby sea turtles are guided by the light reflected on the ocean as they make their way from sandy nests to the water, and birds migrate at night during their seasonal journeys. However, light pollution disrupts these instincts, resulting in an unbalanced ecosystem.
Fortunately, initiatives are in place to help mitigate these issues. In Florida, the Sea Turtle Conservancy works with beachfront properties to modify their lighting, ensuring that baby hatchlings can safely navigate toward the ocean instead of away from it. Additionally, the "Lights Out, Texas" initiative encourages cities to turn off unnecessary lights from 11 pm to 6 am during the spring and fall migration, reducing the risk of birds colliding with buildings due to disorienting light.
Before and after pictures of the Houston, TX skyline. Credit: Texan by Nature
Climate
DarkSky states, "In an average year in the U.S. alone, outdoor lighting uses about 120 terawatt-hours of energy, mostly to illuminate streets and parking lots. That's enough energy to meet New York City's total electricity needs for two years" (2023). They also point out that about 30% of this energy is wasted due to unshielded fixtures, equating to $3.3 billion in costs and contributing to 21 million tons of carbon emissions (DarkSky, 2023).
Earth's atmosphere is already burdened by pollution from cars, factories, and fossil fuels. Some strategies DarkSky recommends to reduce artificial lighting usage include:
- Use timers, motion detectors, and dimmers.
- Choose appropriate light fixtures that minimize upward glare.
- Opt for LED lights, particularly with warm colors (and avoid lights rich in blue).
- Turn off indoor lights, especially in office buildings, when not in use.
Lighting radiance increase over the last few years. Credit: Light Pollution Map
Let’s get back to basics and do our part to restore astronomy to our backyards.
To learn more, check out Dark Sky International and discover how you can become a Dark Sky Advocate in your community.
References:
DarkSky Staff. (2023). Light Pollution Affects Human Health. https://darksky.org/resources/what-is-light-pollution/effects/human-health/
DarkSky Staff. (2023). Light Pollution Harms Wildlife and Ecosystems. https://darksky.org/resources/what-is-light-pollution/effects/wildlife-ecosystems/
DarkSky Staff. (2023). Light Pollution Wastes Energy and Money and Damages the Climate. https://darksky.org/resources/what-is-light-pollution/effects/energy-climate/
Gaskill, M. (2022). Flying Dark: Turning Out Lights at Night is for the Birds. Texas Parks & Wildlife.
https://tpwmagazine.com/archive/2022/may/ed_4_birds/
Light Pollution Map. (2024). VIIRS Country Statistics. https://www.lightpollutionmap.info/LP_Stats/country.html?country=United%20States&type=
Thapan, K., Arendt, J., & Skene, D. J. (2001). An action spectrum for melatonin suppression: evidence for a novel non-rod, non-cone photoreceptor system in humans. The Journal of Physiology, 535(Pt 1), 261–267. https://doi.org/10.1111/j.1469-7793.2001.t01-1-00261.x