Why the Extraterrestrial Chicken Didn’t Cross the Road

Making a Terrible Joke: An Explanation

You might (or, if my audience thus far has been any indication, will) be rather confused at this title. After all, you usually don’t see extraterrestrial chickens in variants of the chicken-crossing-the-road joke. While I assure you that all will be explained by the end of the article, I request you to consider a chicken, attempting to cross the road entitled the Milky Way. The chicken, while extraterrestrial, lives on Earth, and is therefore constrained by our light pollution difficulties. Where might this chicken have success crossing its desired road, and where would it fail to?

Notwithstanding the rather eccentric title, I implore you to go out of your house for a few seconds and take a look at the night sky tonight. If you’re in Singapore (or any other major city), you will likely see almost nothing in the night sky bar the Moon and perhaps a few non-flickering bright spots (these are the planets, which don’t flicker in the night sky because  the light originating from the planets are less subject to atmospheric interference). With the exception of some of the brightest stars in the night sky, such as Sirius, Rigel and Rigil Kent/Hadar, you are unlikely to see stars in the night sky. 

The reason for this should be obvious to the discerning reader (well, the reader who visits a page with the word ‘astronomy’ in it). Light pollution, emitting from Singapore’s buildings, streetlamps, cars and industrial facilities, wash the sky in an orange hue and overwhelms the already-dim celestial objects, making it nigh impossible to view any stars in more populated areas. For reference, I’ve copied a picture I took from Singapore in late 2015, which shows how light pollution colours the sky, even though even it exaggerates the true luminosity of stars in a polluted sky, as a consequence of having a longer exposure. An extraterrestrial chicken, glancing at our sky, would just see a vast expanse of red – enough that if it was law-abiding, it might choose not to proceed on its path.

Orion in a Red Sky (or, why it’s not a good idea to view stars in Singapore)

Light pollution: Not just a ‘clear skies’ problem

Singapore, as a result of its highly urbanised population and rapid development, is widely known to be one of the countries with the highest light pollution in the world. It is, for instance, estimated that 99.5% of all visible stars in the night sky are invisible from Singapore, as a result of our light pollution. This is deleterious to the cause of astrophotography in Singapore as well. A lot of scattered light pollution that won’t show to the naked eye will be very obvious in long-exposure shots, and can significantly reduce star visibility (as an exercise, you can try to see how many stars you can see below the areas with a more reddish hue in the picture). All in all, light pollution is a very common complaint amongst astronomers, and reducing light pollution is likely to be second in astronomers’ wishlists after ‘clear skies’.

Light pollution is unfortunately not just an astronomer’s problem – it has debilitating effects on humans and the environment at large. Light pollution has observable effects on mental health & concentration – circadian disruption caused by over-illumination and other forms of light pollution have been noted by several researchers to have quantifiable effects on bodily function and mental health. You might have heard of this with your phone – your parents or others might tell you to turn off your phone two hours before bed to prevent it hurting your eyes, but this is how – the glare has potential to disrupt your circadian rhythms, having effects such as reducing your ability to sleep. Light pollution even has links to breast cancer. A landmark South Korea study recently drew a link between nighttime artificial lighting and higher breast cancer rates, which appears to indicate even us humans are negatively impacted by the disruptions to our circadian rhythms we’ve caused.

Light pollution can also have terrible effects on the environment and ecosystems – they cause migratory animals to go off track from their traditional destinations, can cause algal blooms, potentially hasten the extinction of several species and otherwise affect most animal processes affected by the diurnal cycle. Light pollution is highly disruptive to animals, especially those living in highly urbanised environments – and urgently disrupts the ecosystem structure in ways that animals (or plants) would have had no time to adapt to. This has been observed in several species, from sea turtles to birds. All in all, the negative effects of light pollution appear to debilitate the health of the environment (something you can say if anyone accuses you of being selfish for wanting to reduce light pollution so you can do some night-time photography!).

Some have suggested that migrating from incandescent light sources to LED bulbs and similar light sources would potentially help mitigate the problem of light pollution. This, unfortunately, must not be taken at face value either. From an astronomical perspective, LED lights may be harder to filter out of our photos – existing camera and post-shot filters rely on wavelength filtering to filter out colours that are typical of incandescent light emission, and it may become more difficult to filter out the wavelengths emitted by LED light. Furthermore, LED is more prone to over-illumination due to the significant energy and cost savings owners will encounter from migrating to LED lights, and thus this migration may even lead to worse light pollution across much of the world. 

Additionally, the skyglow caused by LED lights is significantly more than that caused by incandescent light sources (a commonly-used quantitative estimate dictates that the emissions caused is between four to eight times more intense). This, while damaging to astronomical endeavours, is also environmentally damaging and will potentially lead to even more significant deleterious effects on animal and plant species. Low-sodium lights are commonly thought to resolve this problem better as they provide less skyglow and provide less glare than LED lights do, and correspondingly have been adopted by a limited number of local jurisdictions. 

What can you do as an astronomer?

As an astronomer, beyond working at a broader macro level to improve the implementation of low-sodium lighting, you can adopt steps to improve your own stargazing experience. In many cities (including Singapore) independent efforts have been undertaken to map the skyglow at each site, allowing you to optimally pick a correct site for your stargazing and astrophotography. In Singapore, some good alternative sites to explore when picking a stargazing site include Pulau Ubin and Choa Chu Kang West, and I welcome you to comment if you have any alternative sites to suggest. 

Additionally, do learn about the various techniques you can use to reduce the presence of light pollution in your shots. Narrow-band filters and other camera filters can help you mitigate the effect of light pollution, as can a variety of photography techniques. Using stacking techniques to help process your pictures can also somewhat mitigate the effect of light pollution, due to the reduced exposure time. Some people suggest exposing-to-the-right, which refers to adjusting the exposure upwards to get more light (and later editing to remove excess collected light) but I’ve viewed some evidence that seems to indicate it’s less effective than stacking, so your mileage may vary. I’ll discuss these techniques at slightly greater detail in a separate post.

All in all, I hope you’ve understood the very multifaceted effects of light pollution, and that it’s definitely not only a problem astronomers need to deal with. If anyone ever asks you why the extraterrestrial chicken didn’t cross the road, it’s simple – the traffic light appeared red due to the effects of light pollution. Good luck, and clear skies!


  1. Dominoni, D. M. (2015). The effects of light pollution on biological rhythms of birds: an integrated, mechanistic perspective. Journal of Ornithology156(1), 409-418.
  2. Fujiandstuff. (2017, September 28). Milky Way and light pollution photography tutorial. Retrieved August 15, 2020, from https://fujiandstuff.wordpress.com/milky-way-and-light-pollution-photography-tutorial-using-fuji/
  3. Chepesiuk, R. (2009). Missing the dark: health effects of light pollution.
  4. Luginbuhl, C. B. (2001). Why astronomy needs low-pressure sodium lighting. In Symposium-International Astronomical Union (Vol. 196, pp. 81-86). Cambridge University Press.
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