Why Is the Night Sky Turning Red?

By Guest Blogger | August 23, 2012 12:59 pm

Amy Shira Teitel is a freelance space writer whose work appears regularly on Discovery News Space and Motherboard among many others. She blogs, mainly about the history of spaceflight, at Vintage Space, and tweets at @astVintageSpace

The idea of a red sky at night used to invoke beautiful images of vibrant sunsets, the product of warm sunlight bathing the sky near the horizon. The adage of “red sky at night, sailor’s delight” refers to a calm night ahead; a red sunset suggests a high-pressure system in the west is bringing calm weather. But red skies at night have taken on a new meaning in recent decades. As outdoor lighting become increasingly prominent, our night skies are gradually turning from black to red.

This discovery came from a team of scientists led by Christopher Kyba from the Freie Universitaet and the Leibniz Institute of Freshwater Ecology and Inland Fisheries. The scientists were tracking the effects of cloud cover on light pollution when the realized the colour of the night is changing. Their report, entitled “Red is the New Black,” was just published in the journal Monthly Notices of the Royal Astronomical Society.

Until relatively recently, nights skies were quite dark. The only major source of light was the Moon, allowing us to see thousands of individual stars and the wide, glowing swath of the Milky Way across the sky. Then people started illuminating the outdoors and nights became brighter. Benjamin Franklin helped promote street lamps in the U.S. and improved the designs of these early versions, which were made from candles in glass cases on top of high posts. These were replaced by gas lamps starting in Baltimore in 1816, which remained popular until Thomas Edison introduced the light bulb. Electric streetlights first appeared in Cleveland in 1879 and were the dominant form of street illumination by the turn of the century. As electricity became more affordable, the number of street lamps increased, turning dark city skies into a thing of the past.

This useful light doesn’t confine itself to the paths and streets we want to illuminate—much of it gets scattered by and into the atmosphere. This sky glow is a common phenomenon seen over busy urban areas. Some types of light fixtures produce more of a glow than others. Street lamps open on the top, unfocused lights, and upward-facing lights, like those placed under billboards, drastically increase the amount of sky glow. The more light sent upwards, the more light scattered back down by the atmosphere.

Kyba’s team sought to measure what effect cloud cover has on sky glow. In places where natural light dominates the night sky, clouds typically make those skies darker, just as they do during daylight hours. But the researchers found that the opposite is true in urban areas: Clouds actually magnify the sky glow effect by reflecting more artificial light back down to Earth. They also discovered that sky glow doesn’t just affect night time brightness—it affects the color of the sky as well.

It’s well known that the daytime sky is blue because the atmosphere scatters shorter blue wavelengths of light more than longer red wavelengths. Similarly, the team found that the shorter wavelengths of artificial light are scattered most easily on clear nights. But with cloud cover, the long-wavelength red light that is usually sent out into space on clear nights is scattered back down to Earth.

The result is that cloudy nights in urban areas have a reddish glow. And the size of the effect is substantial. Taking measurements hours every night for months in Berlin, the team found that the blue portion of sky glow is 7 times more radiant on cloudy nights than on clear night, while the red portion is 18 times brighter. In the visual range, that translates to cloudy nights being thousands of times brighter than they are in natural dark night conditions.

This has a significant effect on nature. Animals, humans included, have circadian rhythms—cyclical body clocks that regulate when we should be awake and when we should be asleep. Throw that rhythm off and you get the feeling of jet lag. Brighter nights disturb animals’ circadian rhythms and interfere with natural predator-prey relationships. (This effect is probably minor compared to other nature-unfriendly aspects of cities like heavy traffic and habitat loss.)

Kyba’s team says upcoming technological changes will soon alter how the night sky looks. The current worldwide trend is leaning towards replacing gas-discharge lamps with solid-state lighting like light-emitting diode lights. LEDs are cheaper, last longer, can turn off and on instantly, making them an ideal motion-triggered, energy-saving light source, and they can be directed to light specific areas.

The downside is that because LEDs emit more shorter wavelengths, they might make the night sky still brighter on clear nights. This increase in blue light could have an outsized effect on our circadian rhythms, which are particularly sensitive to the shorter wavelengths.

These bright nights also bring about a less concrete problem: They are taking away our beautiful night skies. The ancients knew the stars and planets with an intimate knowledge most now reserve for their favorite celebrities. A red-tinged sky with a handful of stars is far less compelling than a black night filled with innumerable points of light. Most people living in urban areas will see the Moon and a handful of stars, and if they’re lucky will get a glimpse of Venus, Mars, and Jupiter. That is, of course, assuming they know where to look. And for who know well where to look, like amateur astronomers, sky glow is of course a major annoyance.

The best solution to all these problems—maintaining natural body clocks, cutting down sky glow, and giving us back the night sky—is to change the way cities are lit. Downward-facing lights make a huge difference, and Kyba’s team recommends using “warm white” lights with as little blue wavelengths as possible. But it’s unlikely major changes will come soon. People generally like brightly lit nights, even if it means living under a red sky.

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  • deirdrebeth

    I remember way back in ’91 tossing a football back and forth in front of an apartment window in NYC. We realized after a few tosses that the ball became almost invisible as it passed in front of the window because it was the *exact* shade of the sky. We stopped and held the ball up to make sure it wasn’t just an illusion.

    Nope – pigskin leather is the color of the NYC sky. Whee?

  • Lisa

    Just saying that people “like” living in brightly lit cities is a bit too simple. For many women lighting is essentially equal to freedom of movement.
    Better lighting : yes. More darkness: no.

  • http://atlantarofters.blogspot.com The Sanity Inspector

    I like having ambient light at night, but I do miss the stars. I haven’t seen the Milky Way since elementary school.

  • Feydakin

    Where I live, out in rural America, the nights are still black, and I wouldn’t want it any other way… Not being able to look up into the sky and clearly see the stars, planets and the Milky Way feels stifling to me.

  • bcb

    I live in Liverpool by the Irish Sea,Only ‘ red sky at night’ due to sunset,find picture misleading,nothing to do with streetlamps,just a natural occurance!

  • Jeremy

    … Until Edison *commercialized* the light bulb…

    There, fixed that for you.

  • Darwin’s Chihuahua

    Lisa, well-made point. Think about whether there are ways to overcome this obstacle without compromising too much. There has to be a better way to take care of the safety issue than light up the entire night sky. It would be so nice just to turn off all the lights, use night vision goggles or something similar for those few still out and about, and have vehicles equipped with radar and night vision. It would save so much energy. Use fluorescent, luminescent and bioluminescent pigments and chemicals for marking things. Maybe there could be something like rfid technology interacting with LED lights for emergency vehicles or emergency situations. Perhaps women out walking alone could have spiffier versions of the muslim covering garment, under which they could have ultra-powerful tasers and handgund, all with thumbprint locks. And emergency transponders/alerts/beacons. That plus martial arts training like all the female protagonists in the movies would be quite a surprise. But enough of fantasy. We will probably go along as always, ignoring social and technological innovations that could really change our lives. Pity. I have always loved the dark night sky. It is really a part of our human heritage…

  • Ellen K.

    I live in an urban/suburban area, and the windows in the bedroom where I sleep are to an area that does not have any direct artificial lighting (backyards and an undeveloped area). It’s been obvious to me for a while now that, due to artificial lighting, cloudy nights are brighter than sunny nights. Particularly bright are cloudy nights with snow on the ground. Beats a full moon.

  • Pingback: How to spot Neptune in night sky Friday | Telescope and the Night Sky()

  • Brian

    Here in Rochester, NY… we call that particular color of the sky “Porange”. A beautiful mix of smog and light pollution doubly reflected of the overcast sky and 2ft of snow.

  • lightningbug

    City streets could be far more effectively illuminated while still making the night sky darker than it is now. Street lights should only shine a distance of about two to three streetlights away – if you can see the light directly from a whole block away then that light is just causing glare in your eye, and will make your vision worse.

    Making all of the streetlights brighter doesn’t make anyone feel safer, because of both the glare from far away streetlights and the fact that the ratio in illumination directly under the lamps to in between the lamps stays the same.

    Restricting light to a distance of 2-3 streetlamps and spreading it more evenly on the ground can so greatly improve night vision that you can actually reduce the overall amount of illumination without compromising things like the distance at which you can recognize someone. And if you do that, then we’ll also be able to see a lot more stars, and will save a lot of money.

  • Craig L.

    Lisa: Once we start using more efficient light fixtures that direct the light onto sidewalks & streets, we could cut down on the wattage of the bulbs, cutting down on glare & on the amount of power we’re using every night. That’s how we have less light but better security.

  • annie morgan

    Efficient lighting in a downward fashion will provide just as much safety for those on the streets at night, and light up whatever is so important to be seen. It would be so much better if buildings’ lights were turned off at night. There are three condos north of my place that have brilliant blueish lights on all night – who knows why.

  • Linda Khandro

    Any light that beams sideways or up is wasted light in terms of safety and economies. The sideways beaming light in cities is blinding, as it aims into your eyes (one problem) and creates darker shadows where predators can lurk (another problem). Upward beaming light is only applicable for airport runways and helicopter pads. The overall or general solution is fully shielded light where possible, which beams the light down to the ground in the precise place(s) where it is needed. Stadium lights are not needed when there are no games or practices taking place, but when they are, some shielding can reduce the upward-directed light. Yes, there are up-front costs to cities and municipalities to change their lighting fixtures but once it is done, the greater efficiency over time = lower energy costs.
    Go here for details and success stories (there are some!): http://www.darksky.org/

  • Pat McHugh

    We don’t have that problem in Suffolk, England. The council in our town switches the street lights off at midnight!

  • rond

    Flying into any big city, (NY,LA) you pass through a layer of air dyed a deep red. It appears this is due to pollution, probably from autos. Looking through this from the ground produces the effects discussed.

  • Ashley Shield

    Fact check; First street in the world to be lit was in Newcastle upon Tyne, UK
    http://www.rsc.org/Chemsoc/Activities/ChemicalLandmarks/UK/JosephSwan.asp

  • James Mwagogo

    I research lions in a very large African national park. The light from the stars at night is enough for me to drive in the bush without any other lighting. People who live in developed areas of Europe can have little idea how wonderful is a truly starry night and how many billions of stars there are to be seen. Most European tourists to Africa do not even get to see a truly starry sky while they are there. They stay in lodges with the de rigeur spot-lit water hole and I even see them going for night game drives with vehicle headlamps blazing and hand-held five million candle power lamps making the sky look like blitz era London. Fortunately they encounter few animals; but when they do they must blind the poor beasts for hours. Why don’t they just go and park somewhere in the bush and enjoy the true wonder of the African night instead of charging around in noisy diesel vehicles trying to turn night into day?

  • http://www.onestar-awb.org Audrey Fischer

    Yes, the great news is that starlight can exist over cities too! Keep street lights on target… in a color spectrum that away from the blue spectrum (under 3000K ) and we have solved 80% of the problem (plus saved millions of taxpayer$ and natural resources). For the remaining 20% billboards must be lit from the top-down, same with flagpoles, use motion detectors when appropriate, permit no light trespass off of one’s own property, use more reflective paints and signage at roadways, and enjoy as safer, healthier environment and a beautiful starry night sky. We would save BILLIONS of taxdollars every year in the US alone. Do you know that the National Park Service predicts that by 2025 <10% of people in America will ever see a starry night sky in their entire LIFEtime? This is so needless. Why do you want to give so much $$ to the lighting industry? They have you so buffaloed. There needs to be a total recall of all street lighting with a faulty design throwing off lighting that is off target and harmful to the environment and people. . . at the lighting industry's expense. Did you know that the Amer Medical Assoc announced in June2012 that light pollution is harmful to people's health and recommends "dark-sky friendly" design?

  • Seadog

    As a seafarer crossing an ocean there is no view of the night sky truly more amazing than from the bridge wing or open deck of a ship looking up at a totally un-obscured 360 degree view of the starry night. It is a feeling that one can’t find the right words for, but insignificant comes to mind.

  • NotoriousRoscoe

    Hilarious. We learned this back in 1986 at Army flight school when we were qualifying on night-vision goggles. These “scientists’ act like they discovered it.

  • bbwolf906

    When you live in a rural area and it gets really cold(subzero) , that’s when you get the real night sky show

  • FearTheWeird300 .

    Sometimes I the sky is a dark red around 2:00 in the morning by I live in a town with only 25,000 people.

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