Some Dark News About Bright Nights

By Lindsay DeMarchi and Ken Walczak

New research finds that the night sky is brightening by nearly 10% per year.

In a paper published on January 19th in Science, researchers used over 50,000 observations of the night sky made by community scientists over more than a decade to find that our night is disappearing at an alarming rate. Their results show that over a decade the stars visible to the naked eye have dwindled at a rate previously unimagined. Previous estimates using data from satellite observations pegged the growth of light pollution closer to 3% per year. But since the satellites making these observations cannot see blue light, it was always suspected that number was low.

What makes these results so important? It’s difficult to perceive change that slowly happens over many years or many lifetimes. We may anecdotally feel that we see fewer stars in the sky from when we were younger but being able to quantify that change can turn your instincts into facts. Most importantly, this knowledge gives us the power to project into the future. A 10% annual increase in sky brightness means that every 8 years its intensity will double if left unchecked! A companion piece in Science helps give context for the study.

So, why is this happening? I thought new LED streetlights were supposed to help with light pollution. Streetlights actually contribute a minority of the light flooding our skies - yet still are a source of light pollution. In fact, commercial lighting from parking lots, signage, facades and storefronts may contribute a majority of nighttime sky glow engulfing our cities.

How lights are used has much to do with how much they impact our nights. If they are unshielded or improperly installed, their light shines into our eyes and skies and not on their target. Are they on all night or long after they are needed or are they brighter than they need to be? These are ways the low energy cost of LEDs leads to their overuse. Finally, the bluer the light the more it creates a “light fog” as white/blue light scatters more in the atmosphere and our eyes, robbing us of a view of our universe above.

How can you help reverse this trend and restore the stars?

● You can start local - really local. Are there outdoor lights you own that are too bright, not necessary, spilling out to the neighbors and the sky or could be replaced with warmer colored bulbs? It’s a good opportunity to update your home with light pollution friendly lighting.

● You can share the news. Let your friends, neighbors and lawmakers know that this is something to be aware of and we can help fix it with some simple, informed choices.

● You can magnify your efforts by joining or supporting the IDA, an organization dedicated to improving our world at night.

● Your passion and concern for our natural nights is always welcome here at your local Dark Sky Chicago chapter. Why not join us in saving the stars? Send us a message at info@idachicago.org to get started.