Monday, November 25, 2019

Skyglow hotspots over Chicago

Ken Walczak took this photo of the glowing sky above Chicago's skyline from the base of the Adler Planetarium:

This work by Ken Walczak is licensed under a
Creative Commons Attribution 4.0 International License.

The bright spots show up where near vertically upward directed light enters a cloud. The lights that cause the bright patches are poorly directed, missing their target, contributing to light pollution, and wasting energy without providing any social benefit. Some countries and cities have enacted lighting ordinances or laws that do not allow this kind of lighting. With clever design, it's possible to light building facades without spilling light directly into the sky, saving energy, reducing light pollution, and reducing impacts on wildlife like migrating birds.

Kornél and Zoltán Kolláth have shown that if you know the distance to the buildings, you can use the positions of these glows to calculate how high the cloud base is. In principle, you could use the same method in reverse to figure out which buildings are responsible! But if you're from Chicago, maybe you already have a guess? Feel free to leave your guesses in the comments.

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