Stargazing is awesome! But sometimes, the night sky is not visible due to light pollution. In cities like Nashville, a common type of light pollution is “sky glow”.
Sky glow is the brightening of the entire night sky, especially in populated areas. The light pollution around Nashville inhibits our view of zodiacal light, airglow, and many of the Messier objects.
How can we reduce sky glow? One method for cities to reduce skyglow is to reduce uplighting and excess / wasteful light through shielding or cutoff lights. For other tips, check out this blog by Mara Bermudez.
Shielded Lights
Light fixtures prevent light from immediately scattering in the atmosphere. Many fixtures also aim the light towards the ground, reducing glare and providing better ground visibility. Light shielding also reduces unwanted lighting on other people’s property, called light trespass.
Cutoff Lights
Cutoff lights focus light towards the ground similarly to shielding fixtures. The amount of cutoff determines how much light gets distributed at or above the horizontal. Cutoff lights have many benefits, including focused light for better surface visibility, and less uplighting, which is wasteful and the excess light scatters in the atmosphere.
In Nashville
Many of the street lights at Vanderbilt University are non-cutoff, as shown in this picture on the Vanderbilt admissions page of downtown Nashville. This type of light pollution contributes to the skyglow around Nashville.
Sources
- Dark Skies Awareness: “Light pollution—what is it and why is it important to know?”
- Dark Sky. “Light Pollution”.
- Globe at Night. “What is Light Pollution?”
- Wikipedia. “Light Pollution”.
JSpin 
Great blog post! As someone who has lived near cities my entire life (but who also loves the stars), I frequently become frustrated with the effects of sky glow. I actually had no idea that simply refocusing light could help to reduce sky glow, and I like that you included and analyzed a picture of a lit-up Nashville street. In my experience, national parks and state parks are some of the best places for viewing the night sky with minimal light pollution. Here is a link to a time lapse of the night sky at Pickett State Park in Jamestown, Tennessee: https://www.youtube.com/watch?v=MV4QgD1Y0vU.
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Coming from a suburban area, I can attest that differences really can be as dramatic ans the image suggests. I can drive 15 minutes out of my town and the number of stars I can see triples if not more than that! I wonder if the shielding is in any part a reason for having the hoods on the street lights, or if it is just a coincidence that it helps out observing. Either way, it’s a really simple solution, and I will definitely being focusing way too much on it when I travel.
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