Gaze into the Heavens

Fight Light Pollution!

In a few of my previous posts, I’ve written about my experiences at multiple sites that have been designated as International Dark Sky Parks by the International Dark-Sky Association. I used a Unihedron Sky Quality Meter (SQM-L) to obtain sky darkness measurements in these parks, which included Natural Bridges National Monument in Utah, Capitol Reef National Park in Utah, and Pickett State Park in Tennessee.  I also obtained measurements with the Sky Quality Meter during our stargazing sessions in the Atacama Desert in Chile. This device is scaled so that complete darkness will register a reading of 22.0.  Our Sky Quality Meter registered an astonishing 21.91 reading at Natural Bridges.  At Capitol Reef, we recorded a reading of 21.81, while readings in the Atacama Desert only reached 21.67. Surprisingly, the dark sky meter read 21.31 at Pickett State Park; I expected even the darkest areas of Tennessee to be more light polluted than this.

Unfortunately, light pollution is profoundly affecting the world’s night skies. The Milky Way and all but the brightest stars are now invisible in most urban areas. In 2014, 54% of the world’s population lived in urban areas, and this number is predicted to grow 1.84% annually. This rapid urban growth has caused an increase in urban sky glow, which threatens dark sky views for professional and amateur astronomers. Even in many rural areas, light pollution has dramatically reduced what stargazers can see and what imagers can capture in the night sky. The image below is a map of light pollution in the United States:

It uses data from Light Pollution Atlas 2006, which was created by David Lorenz to update satellite data originally collected by Pierantonio Cinzano and his teammates for the original World Atlas of the Artificial Night Sky Brightness published back in 2001.  Because it uses satellite data from 2006, it isn’t fully up to date, but it is still an instructive tool for gauging the extent of light pollution in a particular area and for finding nearby locations with darker skies.  Here is a link to a webpage that allows you to overlay data from Light Pollution Atlas 2006 onto Google Maps: 


[Link to Google Maps light pollution overlay]  

Using this site, the overlay measures light pollution on a color scale from black, denoting pristine skies, to white, denoting terribly light polluted skies like you would expect to find in the largest urban centers. Using this color scale, Natural Bridges National Monument and Capitol Reef National Park are in black zones. The observing sites in Chile’s Atacama Desert that we visited in June 2015 were on the border between a grey zone and a blue zone. Pickett State Park is in a blue zone.  While black and grey zones are still sprinkled around the western United States, blue zones are often the best we can hope for in the eastern United States, and they are becoming increasingly rare.  

Fortunately, light pollution can be mitigated and perhaps eliminated with the establishment of outdoor lighting codes, so it’s possible that the world’s night skies can ultimately be preserved and even restored for later generations. There are several ways to minimize light pollution, such as the use of shielded low pressure sodium outdoor lighting fixtures that can be filtered out by observers and imagers; the use of shielded, narrow spectrum LEDs for outdoor lighting, by minimizing the use of outdoor lighting in general. The International Dark Sky Association website, which can be found at this link, details ways to minimize light pollution:

[Link to darksky.org website]

Unfortunately, most people are unaware of the negative impact light pollution has on the environment and the views of the night sky. For instance, LED lights have grown increasingly popular in urban areas, but few people realize that broad spectrum LED lights are a bane to astroimaging and observing.  Full spectrum LED lights contribute significantly to light pollution because of the blue light they emit.  Blue wavelengths of light are particularly prone to scattering as they travel through the Earth’s atmosphere, so as cities and towns shift to LED lighting to save on energy costs, it’s especially important to ensure the LED lights they install do not emit light on the blue end of the spectrum.  A much better approach would be to use outdoor LED lighting that filters out or otherwise excludes portions of the blue spectrum that contribute most to light pollution, while providing no real benefit for visibility or security purposes. By limiting light pollution with better outdoor practices, our dark skies can be preserved for generations to come. If you want to measure how light polluted the skies are in your area, you can buy a dark sky meter, which can be found at this link:

[Link to Unihedron website]

In April 2016, I introduced proposed legislation at the Tennessee Youth Legislature in Nashville that would create new lighting standards designed to reduce light pollution in my state. The bill I prepared, a copy of which can be found here, is inspired by and includes provisions from model state lighting legislation developed by the International Dark-Sky Association (“IDA”).  The IDA’s model legislation formed the basis for the new light pollution law that took effect in New York state in 2014.  Its provisions emphasize the placement of shielding on outdoor light fixtures that direct light downward, rather than skyward, and they restrict the spectrum of outdoor lighting to cull out wavelengths that are difficult for astronomers and astrophotographers to filter, or that otherwise interfere with astronomical observing and imaging.

In 2015, I had the opportunity to speak briefly with Tennessee Governor Bill Haslam about recent funding cuts to Tennessee’s summer Governor’s School program for gifted and talented students, and he was very gracious and receptive. I was hoping to get to speak to him again in 2016 about my proposed light pollution bill, but unfortunately, there was no opportunity to do so. It certainly would be wonderful to see my home state of Tennessee enact legislation to help curb light pollution and bring back the night sky.

According to the IDA, at least 18 states have enacted recent legislation aimed at curbing light pollution, including Arizona, Arkansas, California, Colorado, Connecticut, Hawaii, Maine, Minnesota, Missouri, New Hampshire, New Mexico, New York, Oklahoma, Rhode Island, Texas, Vermont, Virginia and Wyoming. I’m confident Tennessee can do the same if enough people work at it..