The night sky is part of humanity's natural heritage. The act of gazing up at the heavens unites all human beings. Have you ever looked up at the sky and felt a sense of wonder?
Modern cities don't have much night sky. The majority of people live in cities today. What can we do to regain our heritage? Can quiet contemplation make a comeback?
Researchers from Spain, Portugal and Italy believe it is possible. The team's new paper, Can we illuminate our cities while (still) seeing the stars?, describes how they could not only keep them well-lit at night, but also open up the night sky for contemplation. You can access the paper on arxiv.org.
The Dark Sky Movement, a global effort to reduce light pollution in cities and improve lighting practices, is an international movement. Proponents of the Dark Sky Movement argue that cities are too lit and that this is not only harmful for humans and their circadian rhythms, but also for nocturnal animals. They claim that too much energy is wasted lighting cities and that light is directed upwards into the sky in a haphazard manner for no good reason. Sky glow is a phenomenon that can block quiet contemplation as well as scientific astronomical observations.
According to the authors, their paper shows that we can create dark skies even in large urban areas by controlling light emission levels and direct glare. They write that these results could be used to support science-informed and democratic public decisions about light usage in municipalities. This will allow for the possibility of observing the night sky from all parts of the planet.
The night-time map of Europe, glittering. This image shows most of the light pollution caused by streetlights. Sky-glow is created by the atmosphere scattering light. NASA Earth Observatory images by Joshua Stevens using Suomi NPP VIRS data from Miguel Romn NASAs Goddard Space Flight Center
For the most part, the Dark Sky Movement has been fighting defensive battles. They have been working to protect the dark skies areas that exist in urban areas. They have worked to reduce light pollution in areas like urban parks, popular star-observing spots and other light-polluted places. These efforts have been successful.
It is not enough. It is not enough for the future and it is not enough for the authors. They write that a reactive, defensive stance is not sufficient to ensure the future of the dark night on the planet. Constantly increasing radiance and illumination of the surface gradually encroaches on dark areas, decreasing their size and natural value.
They are concerned that the future will not have enough dark skies to protect. In many cases, the dark territory to be defended becomes smaller and more fragmentary, thereby breaking the continuity of the nocturnal ecology.
They write in corridors.
Some believe the battle is lost. Some believe that the current levels of light pollution in urban areas is unavoidable. Streetlights provide the majority of light and many argue that roads should be well lit to prevent crime, safety, or to encourage compulsive drinking. These are old facts, and there are no good reasons for us to continue doing things as we are now. Modern research has failed to provide convincing evidence to support road lighting recommendations. This could be for purported safety reasons, compulsive drinking, or even the less well-proven effect of increasing photon densities in order to avoid certain behaviours.
We can all relate to this. However, this scientific paper is not for the faint of heart. The authors go deeper.
These results suggest that starry nights are not inevitable in large urban areas.
According to researchers, there are two questions that naturally arise: What is the maximum light emission level that is compatible with dark urban skies and what is the minimum? What are the compromises?
There are many factors that affect your ability to see stars in night sky. There are many factors that affect the ability to see stars in the night sky. These include the type and amount of light coming from the star and the distance between humans and their eyesight. Researchers claim that all this information can be contained in one number, the luminance contrast threshold. This basically states that if the background luminance is increasing, then the luminance of the object being viewed must increase according to multiple factors.
Night sky is never completely black. Even on moonless nights nature can provide enough background light to help reduce the contrast and make it more difficult for stars to be seen. Nature's background light is part of what we desire to see. It comes from unresolved Milky Way stars and other sources. Artificial light is the problem.
The authors created a simplified scenario that captured the physics of this problem, and then proceeded to analyze it.
The power of sky glow is evident in this nighttime photo of Mexico City. Imagine looking up at the stars in this setting. By Fernando Toms from Zaragoza, Spain Flickr, CC BY 2.0, https://commons.wikimedia.org/w/index.php?curid=348732
Imagine you are in a small urban park of approximately 200m (656ft.). The park is located in the middle of large urban areas with homogeneous light, meaning that there is no dominant directional source of light. Although the park is not lit, it does have some light sources. Because of the tree canopy, the pathway lights do not face the sky or the eyes of the observers. Did you get it? These formulae are used to calculate these variables. The authors provide more details, which interested readers may explore. For the rest of us, let's just picture the park. Imagine if all of the city was like this.
Despite the fact that they believe they have simplified their calculations, there are many variables involved in the authors calculations. The atmosphere changes greatly from one season to the next, as well as from one location to another. The night sky is affected by different buildings and obstacles. Affluent cities produce more light, etc. The researchers came to some conclusions.
What our city night should look like is a political and social decision.
According to them, we can increase the darkness in our urban night-time skies if we make better decisions about what and how much light we use. Although it may sound obvious, there is now data to support and explain this.
It is possible to improve the darkness of urban skies by making a smart choice about the area that will be illuminated.
They conclude the paper by stating that the average spatial density for urban light emissions is approximately 1.2 km. These simplified equations can be used to gain quantitative insight into the trade-offs of emissions and starry sky. These results suggest that starry nights are not inevitable, even for large metropolitan areas.
We must, of course, light up our cities at night. How much light do we need? It seems that we want to have more light and use more energy. What are the advantages of this? It is well-thought out? Is it reflexive or well thought out?
They write that it is socially and politically determined what city night should look like. Artificial light sources create a new reality that is different from natural light. This artificial nightscape should be decided collectively before we choose the technical solutions that will allow us to achieve these goals.
According to the authors, it is time for cities to be more in control of how they are lit. According to researchers, there are no good reasons to continue doing things as they are. It was poorly planned and we were losing our heritage. They stress that the preservation of the night skies is an important issue. Millions upon millions of children around the world don't have the chance to look up at the force of nature and wonder about their lives and the humanity of others.
What will happen if we don't understand the natural world and can't see the sky? Are we courting disaster in our well-lit cities?
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