Light pollution is stealing our skies

Subscribers glow in my own sky, yet make the stars even brighter for me 

Mea Culpa

Oops

In last Thursday’s BAN issue, I had one of those weird brain clouds that’s not really a typo, but kinda is: I was writing about manganese oxides on Mars, and abbreviated it using the chemical notation MgO.

As anyone who took high school chemistry (and, to be fair, also remembers it) Mg is the symbol for magnesium, not manganese, which is Mn. I’ve made that same error before, and when I do make a mistake I try to make a mental note to not do it again, but seriously how often does this specific one come up? It’s hard to correct a behavior with such a long time interval between fouls.

Anyway, I fixed it immediately on the Substack website version of the issue once it was pointed out to me, but the problem is that the issue was also emailed to 1,400+ people, and I can’t fix it there without sending out another email, which would be silly. So I’m taking the time here to say mea culpa — Latin for “D’oh!” — and apologize for any confusion.

SciAm What SciAm

Stuff I’ve written for Scientific American

My latest article for Scientific American is something of great concern to me: light pollution. This is excess light thrown up into the sky from any sort of ground lighting, including streetlamps, advertising signs, cities, houses, and more.

In my article I talk about how this is a problem, and how it’s growing. We didn’t know how quickly things are getting worse until some scientists used a clever method to measure the change in light pollution over time, and found that on average it’s increasing by a staggering 10% per year globally. Read the article for the description of how this was measured.

The basic problem with light pollution is that it makes the sky glow, and washes out the stars. The stars are faint, and we see them clearly because at night the sky is black, so the contrast is high. If the sky itself is no longer black, faint stars and other objects get much harder to see. Go outside when the Moon is new versus full to see this effect very clearly; the bright full Moon swamps the faint stars, and only the brightest are still visible.

This is clearly a huge problem for astronomers — it’s the main reason we build our telescopes far from cities — but as I wrote in the SciAm article it’s a problem for everyone. Light pollution is stealing the stars from us, and that’s a crime.

One thing I had in early drafts of the article was a subtle aspect of this that really worries me: How the lights we use outdoors are getting bluer and why that’s a big problem. My editor and I agreed that some of it had to be taken out, though, because it took too long to explain in an article that was already running long.  But I have a newsletter! So I can talk about it here.

A long time ago, around 2001 or so, I was out driving and came to a flashing red light. I noticed the light wasn’t using an incandescent bulb, as was common then, but instead an LED. This was a relatively new usage of the lights, and I realized how big a deal it was. LEDs don’t have filaments that can break, don’t use much power, are physically sturdy, and are very bright, making them ideal for outdoor lighting. I was happy to see this change and hoped to see more.

A few years later white LEDs became cheap enough for widespread use, and are now commonly employed in self-lit advertising signs, indoor lighting, and more. Again, as this happened I was glad to see it.

But then I read the journal paper measuring light pollution, and got a shock, one of those (haha) light-bulb moments where I realized I missed something obvious, and I almost literally slapped my forehead. The lights we increasingly use to illuminate the night outdoors have a bluer cast than they did before, and that’s very bad.

One reason is how we measure light pollution. Mostly it’s been done using satellites, looking down on Earth at night and seeing how bright things are. These satellites have electronic detectors (digital cameras but much more sophisticated and sensitive than what you have in your phone, say) that measure the amount of light cast upwards from the Earth’s surface below.

In my SciAm article I talk about a couple of ways that isn’t a great way to measure modern light pollution — for example, the satellite detectors aren’t very sensitive to blue light versus red, so as the light we use gets bluer the satellites don’t see it, and undermeasure how much wasted light they see.

But it’s much worse than that. Haze and particles floating in our atmosphere scatter light, like the way a ball bounces off a bumper in a pinball game. A photon of light moving through our air hits a nitrogen molecule, say, and bounces off in another direction. This event is wavelength-dependent; blue light scatters more than red light does. This is called Rayleigh scattering, and is why the sky is blue and the Sun looks red when it sets. I explain this in some detail at The Old Site (there’s a quote block in the middle that got messed up in a site upgrade, making the text invisible; drag your mouse over it to see the words).

And here’s where light pollution gets sneaky. We’re using bluer lights these days in streetlights, city lights, billboard signs. The lights are on the ground and cast their glow upwards. But a lot of this light is then scattered back toward the ground. From your point of view, it looks like the sky is glowing even more brightly, because your own light is being reflected back down to you.

I didn’t think of this in my original assessment of LEDs. The bluer light is making light pollution even worse than if they were simply brighter. That blue light is an added multiplier to the pollution problem. It’s obvious to me in retrospect but not something I considered back then.

I’m not saying we can’t or shouldn’t use them! We just need to be more intelligent about this, using lamps that are better shaded to light up the ground and not the sky, keep window shades closed at night, turn off lights when they’re not needed (how many parking lots in towns are lit like a football arena at midnight?), and so on. Using lights more cleverly pays off in lower electricity costs, safer environments (overly bright lights cast overly dark shadows, and our eyes adapt for the bright light making the shadows even darker, where danger can lurk), and is better for our own health. I have many links in the SciAm article about how this works and what can be done.

And something very much needs to be done. If you’ve never been to a truly dark site, you don’t know what you’re missing. The utter blackness of the sky brings out the glittering shine from a thousand nearby stars in our galaxy, with the luminous glow of the Milky Way hanging like a dream overhead, punctuated by the occasional meteor streaking across the starry vault. It’s magical.

And it’s going away. Light pollution isn’t a joke; it harms us, it harms plants and wildlife, and it’s drowning our sky. The first step in fixing this problem is being aware of it. The second is educating yourself — poke around the International Dark Sky Association site to find out more — and the third is taking action. The IDA site has info and advice on how to talk to your local town/city council and more, and what actions we can take as individuals to help.

I love the sky so much, and I want to keep it. For my own enjoyment, of course, but especially for yours. It belongs to all of us, and it’s up to us to preserve it.

Et alia

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