When we look at the night sky nowadays, most of us hardly see any stars. They are hidden behind the artificial lighting that we have created to keep the night away. Why light pollution matters.

The year was 1833, it was late at night. Throughout North America people woke to the sounds of commotion in the streets. When they brought their gaze up, they found the sky illuminated by hundreds of spectacular 'falling stars' - a shower of hundreds of thousands of meteors per hour! The cries of enthusiasm lasted for many hours, until the morning light hid the colorful light show and left millions of amazed people tired after a sleepless night. Excited newspaper headlines about what was named “the night the stars fell” reached as far as Europe.  

Summer of 2020. The Earth passed through the trail of dust left behind by comet Swift-Tuttle, and the night sky should have displayed the prolific Perseids meteor shower, as should have happened every year. Unfortunately, the light pollution in most of the densely populated areas on our planet did not allow the majority of its inhabitants to observe the delicate light trails created by the meteors as they heat up rapidly upon entering the atmosphere. Thousands flocked to thinly populated areas, hoping to find a dark corner to allow them to watch the meteor shower. Headlines in some countries reported extraordinary traffic and night campsites at full capacity.  

Light pollution not only deprives us of aesthetic pleasures, but also encompases the entirety of the negative effects of artificial light. It hides the night sky, harms us in a variety of ways and is also harmful to ecosystems. There are, however, quite a few solutions to this problem, the implementation of which could save a lot of money. 

מטר הלאונידים של 1833 נצפה בערים החשוכות בדרום ארצות הברית תגליף של אדולף וולימי | מקור: ויקיפדיה, נחלת הכלל
The 1833 Leonids meteor shower, seen in the dark cities of southern United States, engraving by Adolf Vollmy | Source: Wikipedia, common knowledge

The Disappearing Darkness

From the dawn of human history humans have looked at the sky in amazement. Even prior to the formation of cities, stargazing was the best show in town. Countless religions and cultures have developed entire methods and rites around the attempt to understand the celestial bodies, which have, over the course of history, remained a source of significant  scientific and technological developments. The stars sparked the imagination of the ancient Greeks, who have built a glorious mythology around them, and the star systems identified by them continued to guide European explorers while navigating the unknown many years later.  

The stars also inspired artists who have created wonderful works of art, such as the playwright William Shakespeare or the painter Vincent van Gogh. The motion of stars and the observations of Galileo Galilei were at the heart of the scientific revolution of the 17th century, and astronomical research has even led to the development of the digital camera that has changed our lives in the past few decades.

ציורו של וינסנט ון-גוך "שמיים זרועי כוכבים" | מקור: ויקיפדיה,  נחלת הכלל
The sky as a source of wonder and knowledge. Vincent van Gogh’s painting “The Starry Night” | Source: Wikipedia, common knowledge

These days, the abundant illumination in the night sky in nearly any populated area creates a constant light pollution, which drives us away from the wonder and the glorious heritage of daily stargazing. According to measurement-based estimations, nearly all residents of the U.S. and Europe live in areas with significant light pollution. About a third of Earth’s population and almost four-fifths of the population of the U.S. have completely lost the possibility to see the Milky Way galaxy that we inhabit, with their naked eyes, and in some countries matters are even worse.

מפת זיהום האור בעולם | מקור: אטלס הבהירות של שמי הלילה
Many residents, mostly in the west, see very little of the night skies due to light pollution. A light pollution map of the world | Source: The new world atlas of artificial night sky brightness

Why do we hardly see the stars anymore?

The light arriving from most stars is very weak and in order to see them and most other celestial bodies a sufficiently dark background is necessary. A white dot is easily noticeable on a dark background, but it is difficult to spot  it on a light background. As light from the ground illuminates the sky, the background of the stars becomes brighter, and the contrast between the stars and their background is diminished. The dimmest stars disappear first, and the more severe the light pollution becomes the more and more stars will disappear from our eyes. The bright streaks of meteors that burn high in the atmosphere disappear along with them. 

The visibility of stars is not only affected by their background, but also by any light existing in our field of vision. Our eyes adjust to light conditions such that the more light enters the eyes, the more the pupils shrink and the less light penetrates through them and reaches the receptors in the eyes. The sensitivity of the light receptors also changes according to the light conditions. Sensitive receptors, called Rods, allow us to see at night, but they require a long adjustment time to darkness. That is why even a quick glance at the bright screen of one’s smartphone will suffice to reduce the amount of stars visible to one’s eyes for long minutes

Proportional lighting?

There is no doubt that night lighting is important. It provides us with a safe  and secure environment at night, allows us to lead an active nightlife, helps us to see the night roads and highlights signs and important sites. Every lighting has its purpose, but poor and inaccurate planning makes it a nuisance. According to activists from the International Dark-Sky Association, the main problems are light sources that are directed towards the sky, lighting that exceeds the area necessary to be lit or the required lighting duration, as well as excessive or dazzling lighting. Unfortunately, most light pollution could have been prevented with proper planning. 

Planning defects can even harm the purpose for which the lighting was originally designed. Imagine what would have happened if all cars would constantly drive with high beam headlights, or if their headlights would point in all directions. Even excessive or badly directed street lighting can dazzle drivers and cause difficulties to road users. And the problems do not end there. Visible light, that is, the range of electromagnetic radiation we are able to see, is not well absorbed in the atmosphere, which scatters it in all directions. That is how our cities and roads spread their glow to the sky to the sky even tens of kilometers away.

Ecological and astronomical light pollution, from a report by The Israeli Society of Ecology and Environmental Sciences
Ecological and astronomical light pollution, from a report by The Israeli Society of Ecology and Environmental Sciences


Pollution From Above

In order to avoid light pollution and other disturbances, it is customary to place scientific telescopes on distant and dark mountains.  However, a new type of light pollution threatens to disturb even these remote oases of darkness. In the coming decade nearly 80 thousand communication satellites are expected to enter the Earth’s orbit, which is about ten times the amount of satellites as of mid-2021. These satellite arrays are designed to connect to the Internet even the most remote regions on Earth, which are not financially viable to connect via fiber optics. But there remains a fly in the ointment - these satellites reflect sunlight, among other directions towards the ground, and they thus glow, similar to the moon. Therefore their presence generally alters the night sky, making it difficult to perform astronomical observations. 

Engineers have changed the design of these satellites to reduce the intensity of the light reflected from them. However, results have so far been unsatisfactory, as they keep blinding telescope sensors. Most Internet satellites are launched into low-altitude orbits, and the Earth’s shadow hides them from the sun during certain hours of the night. However, above a fairly modest altitude of 600 kilometers, satellite arrays blind sensors almost permanently, severely hampering the ability to conduct astronomical research. Most communication satellites cruise at much higher altitudes of 35.6 thousand kilometers.    

According to Jonathan McDowell from the Harvard-Smithsonian Center for Astrophysics in the U.S, “Starlinks [low altitude satellites] are really annoying but manageable”, whereas “OneWeb [high altitude telescopes] is just ‘Pack up your telescope and go home’.”

Radio telescopes are expected to experience an even greater disturbance from the dramatic increase in the amount of communication satellites. Internet broadcasts  use wavelengths similar to those measured by these telescopes, but at an intensity that is a million times higher than that of the celestial bodies they search for. Thus, a communication satellite transmitting in the direction of a radio telescope could even destroy its sensitive machinery. 


A stack of multiple consecutive exposures, across a 30 minute timespan, captured the trails of Starlink satellites over Bryce Canyon, Utah, USA. [Spencer’s Camera and Photo]

Innocent Victims

Humans are not the only ones who look at the night sky and watch the stars. Birds, seals and even dung beetles use stars for navigation as well, and may lose their way if unable to see them. In a recently published study researchers demonstrated that dung beetles, who usually roll their dung ball in a straight line, begin to walk in circles when exposed to significant light pollution. Hatchlings, sea turtles that have just hatched on the beach, get disoriented by city lights and do not find their way to the sea. 

The harm of light pollution to animal life does not amount only to impaired navigational ability. Nocturnal insects, such as moths, are deterred from flying in highly illuminated areas, where they are exposed to predators. This makes it difficult for them to forage for food, and indirectly harms plants, which depend on these insects for pollination. A study published four years ago demonstrated that street lighting can significantly impair the reproductive capacity of plants, and subsequently also that of the animals that feed on them.

Light pollution seems to reach even the seas and oceans, affecting all living beings in them. A research performed on Anemonefish (Amphiprion ocellaris), or the ‘ocellaris clownfish’ featured in the movie “Finding Nemo”, found that their eggs always hatch during the night, in order to improve the chances of the larvae to escape predators. When the eggs were exposed to 24-hour illumination, they simply did not hatch. 

It seems therefore that we find negative effects of light pollution on animal life everywhere we look. There is no doubt that further research will uncover more such effects in the future. 

A Problem Worth Solving

Light pollution also involves a huge waste of money and electricity, and therefore it would be cost-effective to treat it. Existing solutions focus on careful lighting design to illuminate only what is necessary. Designated light sources can prevent light from leaking towards the sky, residential homes and other unwanted places. Timers and motion detectors make it possible to turn on lights only when necessary. Using power saving light bulbs with a warm shade and appropriate intensity makes it possible to further reduce light damage and power consumption.   

Mapping light pollution helps focus on the most problematic places. International endeavours such as the International Dark-Sky Association (IDA) and citizen science campaigns such as Globe at Night, help to raise public awareness to the problem and allow the public to help map light pollution worldwide. Accurate mapping leads to the designation of more and more places on Earth as International Dark Sky Parks - areas possessing an exceptional quality of starry nights. The IDA also designates communities which have shown exceptional dedication to the preservation of the night sky as International Dark Sky Communities, to promote responsible lightning and encourage such preservation in more and more places.   

It seems that similar to many other environmental issues, here too the ball is in our hands. We must warn against light pollution and point out ways to reduce it. Among other things, it is possible to reduce light leakage around our homes and workplaces. Here too the greatest influence lies in the hands of decision-makers, even at the municipal level, since a significant part of light pollution comes from public lighting, and professional planning can greatly reduce it. Additionally, dedicated laws can also reduce light pollution emitted from private lighting enterprises, and many countries have already begun to implement these.