Stars can’t fight city lights.  They’ve turned their backs on us.

A hundred years ago, just about anyone could walk outside into their yard at night, look up, and easily see the Milky Way.  But now we all take for granted that you can’t see any but the very brightest features of the night sky from urban and even suburban areas because there’s simply no getting around all the light pollution.  It’s just the cost of doin’ business.

But that thinking is beginning to change.  

In September 2021, my beloved Pittsburgh became the first major city to rethink how urban lighting will be conducted, passing a dark-sky ordinance not only for visibility of the night sky but also to use less energy, to help plants and animals by maintaining a crisper day-night cycle, to reduce glare for better night vision, and to benefit those in poorer neighborhoods who are disproportionately negatively affected by wasteful overlighting. 

I’m so proud of you, Pittsburgh!  I hope your action will lead the way for cities across the United States.

Milky Way over Pittsburgh
Dreaming of the Milky Way over Pittsburgh

Lest you think this is idle talk, the city is getting started on this now:

The city is reviewing bids to choose a vendor by the end of the year to replace all of its 35,000 streetlights, as well as add 8,000 new ones in the recommended color temperature around the city, according to the mayor’s office.

The ordinance will also affect all newly installed lighting at City-owned buildings, parks, and other properties, requiring dark-sky principles to be observed.  Happily, other institutions around the city are already getting into the spirit and joining the effort:

The Pittsburgh Zoo and PPG Aquarium, Phipps Conservatory and Botanical Gardens, and the National Aviary have already announced they will adopt the ordinance on their properties.

Yes, you read that right:  The National Aviary is indeed located in Pittsburgh!

Hatching of a rare Andean condor in 2019 at the National Aviary as part of an effort to help the species survive

But why Pittsburgh?  Why now? 

It largely arose out of the efforts of astronomer Diane Turnshek and architect/urban designer Stephen Quick, both special lecturers at Carnegie Mellon University.  In an interview with NPR’s Morning Edition a couple of weeks ago, Turnshek explained:

When I grew up in New England, you could just walk outside and look up and see the Milky Way.  But when I arrived in Pittsburgh, the sky had started to decline in quality.

Forty years later, I have to explain what the Milky Way is and describe what it looks like — you know, show pictures.  And [my students] think those pictures are fake.


In August, the astronauts on the International Space Station took some pictures of Pittsburgh for me on a clear night.  And that’s the “before” shot.  The astronauts are going to continue to take pictures of Pittsburgh, so we will have “during” pictures and “after” pictures.

Here is that “before” picture (which looks a lot better in full size):

Photo of the Pittsburgh metro area at night from the International Space Station, Aug. 1, 2021

And here is Carnegie Mellon itself at night:

Carnegie-Mellon University at night
Carnegie Mellon University and Phipps Conservatory (lower left) at night.  All the light you see is pretty, but ultimately wasted

CMU goes on to explain:

Dark-sky lighting uses technology like motion sensors, dimmers and timers, cooler temperature bulbs, and shielding — which makes sure light is directed down instead of up — to reduce light pollution while providing enough lighting for safety and comfort.  

The city plans to retrofit existing streetlights to dark-sky-compliant LED lights. Pittsburgh’s current 4,300 LED streetlights glow at 5,000 kelvins and give off a bright blue-white glare.  The new LED lights will be at a lower temperature and look much softer and warmer, as recommended by the International Dark-Sky Association.

The notion of “light temperature” has to do with black-body radiation.  Let’s say we have an opaque metal sphere that doesn’t reflect any light (a “black body”), and we heat it so hot that it glows.  The higher the temperature it reaches, the shorter (bluer, more-energetic) the wavelengths of visible light it will emit. 

Stars behave pretty much like black bodies, so we can use the color of a star to get an idea of its temperature:

Temperatures shown in kelvins (K).  To get degrees Celsius, subtract 273.15 (3000 K = 2726.85°C).  That in turn is about 4940°F.

The colors above are way exaggerated for clarity; in reality the range of star colors actually looks more like this:

Hydrogen-fusing (“main-sequence”) stars of different types

Stars emit all wavelengths of visible light, so they all look more-or-less whitish, but the tinge of their color depends on what visible wavelengths they are emitting more of.  Ninety percent of stars are simply fusing hydrogen into helium, and this makes them “main-sequence” stars.  The bigger the main-sequence star, the hotter it’s going to burn.  A larger star feels a stronger crushing force of gravity within it.  That pushes more hydrogen to fuse, generating more outward pressure to keep the star from collapsing, but also generating more heat.  So the bigger main-sequence stars are hotter and thus appear bluer.

We use the same color scale to describe the radiation profile emitted by light fixtures.  No, that doesn’t mean your yellowish bathroom light has the same surface temperature as the Sun!  It’s just that its emission spectrum makes it look about equivalent to a black-body radiator at that temperature.  You can see below that the range of LED light colors of various “light temperatures” is not unlike that of stars.  They too are emitting all wavelengths of visible light, but it can be slanted toward red or blue:

I’m sure you’ve seen city lights that look like that top one

So we want to “cool down” that light temperature.  Turnshek explains:

What we’re trying to do is cut out the light at the blue end of the spectrum because blue light scatters more easily than red light in the atmosphere, right? That’s why the sky is blue. So blue light scatters everywhere. It doesn’t stay where you’re lighting.

A bit more on the benefits of efficient and cool urban lighting from Pittsburgh Magazine:

Humans are dependent on natural internal cycles such as the circadian rhythm and the production of melatonin, which are regulated by the natural external cycles of the environment. But the truth of our bright world is that most people in the U.S. no longer experience genuinely dark nights.  When exposed to artificial light — especially blue light, and especially at night  — these cycles are disrupted, according to research posted on the International Dark-Sky Association (IDA)’s website.

Further, IDA estimates that $3.3 billion in outdoor light is wasted per year, and also releases 21 million tons of carbon dioxide.  To offset the environmental effect of all that carbon dioxide, 875 million trees would need to be planted annually.

In a heatmap produced in conjunction with The New World Atlas of Artificial Sky Brightness, Pittsburgh is identified as a light pollution hotspot.

Well, aren’t we all?

Gack, look at New York

I should point out that Pittsburgh isn’t merely humoring itself.  The International Dark-Sky Association is pleased with the City’s effort and is fully on board:

“Pittsburgh is the first city to take a principles-based approach to legislation, clearly aligning with IDA’s values-centered approach to lighting”, said Ruskin Hartley, Executive Director of the International Dark-Sky Association. “The [now-passed] ordinance [provides] policy that is easy to understand, implement, and enforce.  We foresee this approach serving as a model for other municipalities looking to effectively reduce light pollution.”

I hope other cities will join the effort soon, too!

Finally, to sum all of this up better than I could, we have a very on-point letter to the editor of the Post-Gazette from someone who should know:

Oh, these silly astronomers!  They can’t see the stars over Pittsburgh, so they enlist the help of Mayor Bill Peduto to craft an ordinance to make the skies darker.

So if they want to see their stars, why don’t they just go out in the country?  We need our lights to be safe.


But wait!  These astronomers are onto something.  And if we follow their plan, we all will reap the benefits.

Proper nighttime lighting from shielded fixtures keeps illumination from pouring into the sky.  It also improves visibility on the ground, making our streets and highways … safer!  These shielded fixtures keep the light from shining into our eyes, thereby making it easier to see.

Because less energy is wasted, we don’t have to pay for outrageous electric bills.  Take a look at a cloudy night over the city.  See the white bottoms of the clouds?  We should all be appalled at that waste.

Proper nighttime lighting also benefits animals and plants, which have evolved, like humans, in a day-night cycle.  Living things need the dark just as much as they need the light.

By reducing nighttime lighting, we also can improve human health.  Read about the adverse effects bad nighttime lighting has on the body’s production of melatonin and the corresponding increase in cancer rates in humans.

Before you pooh-pooh my illuminating claims, look into the research and take it for its proper worth.  The International Dark-Sky Association at is a great place to start.

Let’s work together to manage our lights properly.

Palm Harbor, Fla.
The writer is a retired Post-Gazette news editor who also wrote about astronomy for the newspaper.

See the full-screen version HERE

Can an urban area like Pittsburgh really reduce its light pollution substantially?  Will private properties in the city catch on and make it the cool thing to do?  Will kids in the Pittsburgh area grow up with an enhanced interest in astronomy and the Universe because of all this?

Let’s hope so.  I’m really enthused to see that an earnest effort is underway.  The Steel City is on its way to becoming the Star City!

Before I go, I must give credit to the artist from whom I stole the first line of my diary…

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This is a Creative Commons article. The original version of this article appeared here.


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