Protecting Dark Skies

When was the last time you looked upon the beauty of the Milky Way? Have you ever even seen the Milky Way? It is estimated that about 80% of the U.S. population lives in areas where the Milky Way is completely obscured by light pollution.

The impact of light pollution at a given location is represented by the Bortle Scale, which ranges from 1 to 9. Lower Bortle numbers provide darker skies, which increases the opportunity to view more stars and celestial objects.

Image taken in 2012 from the Suomi NPP — VIIRS instrument. Credit: NASA Earth Observatory website

As an example, downtown Chattanooga is a Bortle 8/9 while our Harrison Bay and Cloudland Canyon public star parties are held in Bortle 5 and Bortle 4 skies, respectively. To put things into further perspective, the closest Bortle 3 skies are about 40 miles to the northeast of downtown Chattanooga while the closest Bortle 1 skies are probably about 1,000 miles away in either Canada or Texas.

So, what can we as individuals do to help reduce our impact on the night sky? The simplest positive action would be to assess the lighting at your home and/or business and change over to “dark-sky approved” light fixtures. Even this small step can make a significant difference in mitigating light pollution.

This illustration of the Bortle Scale is a modification of an original photograph taken at European Southern Observatories' Paranal Observatory in Chile. Credit: ESO/P. Horálek, M. Wallner

Five Lighting Principles for Responsible Outdoor Lighting:

  1. Useful - Use light only if it is needed

  2. Targeted - Direct light so it falls only where it is needed

  3. Low level - Light should be no brighter than necessary

  4. Controlled - Use light only when it is needed

  5. Warm-colored - Use warmer-color lights where possible

DarkSky International diagram presenting the benefits of shielded lights.

We will never be able to change downtown Chattanooga into Bortle 1 skies, but every small positive change in lighting can help us take a step closer to a lower number. For more information about protecting our night skies and light pollution, please visit the DarkSky International website.

“You and I are made of stardust. We are the stuff of exploded stars. We are therefore, at least one way that the Universe knows itself. That, to me, is astonishing.” - Bill Nye

Image Credit: BAS Member Matt Harbison