Dark skies allow us to study the universe, support the natural rhythms of life, and experience the wonder that has connected people to the stars for generations. Learn why natural darkness matters—and how thoughtful choices about outdoor lighting can help preserve it.
Dark skies are night skies that remain free, or mostly free, from artificial light. Streetlights, building lights, billboards, and other outdoor fixtures can brighten the night beyond natural levels. Where natural darkness is preserved, stars remain visible, ecosystems follow their normal nighttime rhythms, and people can experience the night sky as it was meant to be seen.
When Williams Bay was selected as the home of Yerkes in the late 19th century, its clear skies—far from the industrial pollution and growing lights of Chicago—made it an ideal place to study the universe. These conditions allowed Yerkes scientists to conduct groundbreaking research and helped establish the observatory as a world leader in astronomical discovery.
Dark skies remain essential to astronomical research today. Under naturally dark conditions, telescopes can capture dim stars, distant galaxies, and subtle details that disappear against a brighter sky. As development and artificial lighting expand, skyglow makes these objects harder to detect, shortens effective observing time, and limits the accuracy and scientific value of the data collected.
For billions of years, plants, animals, and humans have evolved in sync with predictable patterns of daylight and darkness. This natural cycle helps regulate when we sleep and wake, when animals hunt or rest, and when plants grow, flower, and conserve energy. Artificial light at night can disrupt these biological signals, affecting sleep, feeding, reproduction, migration, and seasonal behaviors.
The effects can ripple across entire ecosystems. Nighttime pollinators may be drawn away from their habitats, plants may experience altered growth cycles, and animals can become disoriented or more vulnerable to predators. Migratory birds are especially at risk: artificial lights can pull them off course, cause exhaustion, and contribute to fatal collisions with buildings.
For most of human history, the night sky was a familiar part of everyday life. Across cultures and continents, people used the stars to navigate, track the seasons, mark important occasions, and pass stories from one generation to the next. The night sky inspired curiosity, reflection, science, art, and mythology.
Today, artificial lighting has made this shared experience increasingly rare. In many places, only a handful of stars remain visible, and entire generations are growing up without seeing the Milky Way. Preserving dark skies protects more than scientific research and the environment—it safeguards a meaningful connection to our shared human history.
Outdoor lighting should provide safety and visibility without unnecessarily brightening the night. Choose warm-colored bulbs with a correlated color temperature of 2700 K or lower. These warmer tones produce less glare and skyglow and are less disruptive to natural day-and-night cycles than cooler, blue-white light.
Brightness matters, too. Most pathways, porches, and yards need far less light than people expect—often just 300 to 800 lumens. Keeping outdoor lights below 1,000 lumens can improve nighttime visibility while reducing wasted light and excessive brightness.
Fully shielded fixtures direct light toward the ground, where it is useful, rather than allowing it to spill into the sky or onto neighboring properties. This reduces glare, improves visibility, and helps limit skyglow.
Timers and motion sensors can further reduce wasted light by keeping outdoor fixtures off when no one is using them. Turning lights off after a set time or activating them only when movement is detected creates a safer, more comfortable nighttime environment while preserving the darkness above.
Small changes to the way we use outdoor lighting can make a meaningful difference. Tell us why dark skies matter to you, share the steps you have taken to reduce light pollution, and inspire others by submitting a photo of your dark sky-friendly lighting.
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