Night Skies

 

The Milky Way bends above the silhouetted horizon in this panoramic view at Black Canyon of the Gunnison National Park.

NPS/Bettymaya Foott

 

Visitors observing the night sky during AstroFest

Photo by Joyce Tanihara

The Value of Night Skies

The night skies in national parks are a protected park resource just like plants and animals. They are a natural resource; many natural processes rely on the cycle of light and dark. They are also a cultural resource. People have been viewing the skies for thousands of years and shaping beliefs, traditions, navigation, and wayfinding. Night skies are also a wilderness value.

Effects of Light Pollution

Light pollution affects more than just astronomers and night sky enthusiasts. It is a widespread challenge across the globe. Sky glow is the increase in the brightness of the night sky that can reduce visibility. Natural sources of sky glow exist, like a bright full moon, but human-made sources are the largest concern. Lights from homes, buildings, parking lots, stadiums, and businesses can increase sky glow and create the "dome" of light seen above populated areas.

Nocturnal animals need darkness for survival. Light pollution can disturb natural behaviors such as hunting and migration. Circadian rhythms of humans and plants also rely on an unaltered night sky.

 

Click above for a larger image. Dark and lighter blue shows less light pollution. Green and yellow shows more light pollution.

NPS

Protecting Night Skies

Though light pollution is created by a multitude of lights, these problems can be resolved one light at a time.

Black Canyon preserves a dark sky largely unaltered by modern infrastructure and technology. The park strives to protect the night sky by only using artificial lighting necessary for safety. Motion detectors limit the light needed within restrooms and other areas in the park. All outdoor lighting devices use low-energy, low-impact bulbs with shields that direct light to the ground where it is needed. Inventory monitoring is conducted to ensure lighting continues to be compliant and night sky friendly.

National park sites preserve some of the country's darkest night skies. Due to its exceptional night skies and efforts to mitigate light pollution, Black Canyon of the Gunnison National Park was designated as an International Dark Sky Park in 2015. The park is one of many in Colorado with a designation from DarkSky International.

Park rangers, volunteers, and members of the Black Canyon Astronomical Society (BCAS) work together to provide astronomy programs. These programs focus on light pollution and night skies education, constellation tours, telescope viewing, and more.

Measuring Darkness

How dark is dark? Dark Sky designated locations typically use sky quality meters (SQMs) to measure the darkness of their sky. Readings are usually taken at zenith (the point in the sky directly overhead) and at four other slightly lower points in the sky. SQMs read sky brightness in magnitude per square arcsecond - the higher the number, the darker the sky. The highest possible rating is 23.

As of 2019, parks must have an average reading of 21.2 or higher to be eligible for consideration through DarkSky International. Black Canyon readings have historically averaged 21.5. Readings approach 22 at park sites such as Great Basin, Big Bend, and Natural Bridges. Big cities such as Denver, Colorado have readings around 18.

 

Your Night Skies

Wondering how you can help? Be an advocate for your night skies at home. Here are simple ways you can protect the night.

Shield your lights
Use full, cut-off light fixtures at your home or business. Existing lights can also be adjusted to point downward or retrofitted with simple metal shrouds.

Use lights only when you need them
Motion sensors and timers are a great way to turn on or off lights as needed. This costs less, improves security and visibility, and reduces light pollution.

Use less light
An effective, shielded light fixture can use a smaller wattage bulb and still be effective.

Talk to your neighbors
Share your appreciation of the night sky with family, friends, neighbors, and community leaders. Encourage action towards reducing light pollution through small, positive changes.

DarkSky International provides more information on ways to get involved with night sky protection.