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Darkness and the night sky

Part 2 of 3

Mark DiVecchio

Special to the Village News

Chapter 2 – Why darkness is important (and not just to astronomers)

Circadian rhythm and melatonin

Like most life on Earth, humans adhere to a circadian rhythm – our biological clock. It's a sleep-wake pattern governed by the day-night cycle. Our biological clocks are important. They interact with our body systems, changing our hormone levels and even modifying our genetic code.

Natural light helps set our clocks to Earth's 24-hour day-night cycle. Exposure to artificial light at night disrupts this process, increasing our risks for cancers and other potentially deadly diseases.

Blue-rich light at night is particularly harmful. Most LEDs used for outdoor lighting, computer screens, TVs, and other electronic displays emit abundant blue light.

"Many species (including humans) need darkness to survive and thrive." – American Medical Association

Glare impairs your vision

Glare from poorly shielded outdoor lighting degrades your vision by decreasing contrast. This limits your ability to see. Aging eyes are especially affected.

"Glare from nighttime lighting can create hazards ranging from discomfort to frank visual disability." – American Medical Association

Artificial lights disrupt the world's ecosystems

Sea turtles live in the ocean but hatch on the beach at night. Hatchlings find the sea by detecting the bright horizon over the ocean. Artificial lights can draw them away from the sea, stranding them on land. In Florida alone, millions of hatchlings die this way every year.

Many insects are drawn to light, but artificial lights can create a fatal attraction. Declining insect populations negatively impact all species that rely on insects for food or pollination. Nocturnal mammals sleep in the day and are active at night. Light pollution disrupts their nighttime environment.

Artificial lights endanger many bird species

Artificial lights can disrupt the migratory schedules of birds causing them to leave too early or too late in the season, missing ideal conditions for nesting. Birds that navigate by moonlight and starlight can wander off course. Millions die every year by colliding into illuminated buildings.

Acknowledgment: This series was produced with help from the International Dark Sky Association,

Next time, Chapter 3 – What we can do to keep the sky dark

Anyone interested in supporting FBA's Dark-Sky initiative can sign their on-line petition at


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