A study carried out by the Globe at Night project – a citizen science program involving more than 50,000 observations from volunteers around the world – has found that the brightness of the night sky has increased by 7 to 10 per cent a year for the last decade.

We spoke to Dr Greg Brown, an astronomer based at the Royal Observatory Greenwich, about what this trend means for laypeople, astronomers and animals, and if it can be reversed.

How bad is the situation? Are we looking at a potential scenario where future generations won't be able to enjoy looking at the stars without travelling to designated areas?

It is a great shame that a lot of people are denied the view of the night sky. In the planetarium that we run here at the Royal Observatory, we often start some of our shows with an estimate of the current light pollution around London. Even in our relatively dark site in the middle of a park we still have to deal with Canary Wharf and the main parts of the city around us. When we compare that situation of light pollution to what the night sky would look like from a dark sky site, the differences is massive. There’s absolutely no doubt that that's going to have an impact on our appreciation of the night sky.

The brightest objects in the sky [such as planets] are going to be visible beyond any reasonable level of light pollution that we could ever reach. But the fainter objects in the sky, the array of stars in the Milky Way, for example, are already basically impossible to see from suburban areas let alone the centre of cities. So, yes, light pollution is very much hampering the ability of the average person to be able to explore the cosmos.

So how do we go about measuring the amount of light pollution?

With some difficulty. A lot of the past studies have been carried out using satellites which are great for analysing red light, but struggle somewhat with blue. This is a problem as modern light pollution tends to be blue light as a result of replacing sodium lamps, for example in street lighting, with LEDs. So a lot of studies nowadays have to be done from the ground in order to be able to make up for that. That is where the citizen science angle comes from in this project. There simply aren't enough people studying this sort of thing around the world. So there has to be a certain amount of involvement from the general public to make up that deficit.

When did this trend start?

Light pollution has become an increasing problem since the seventies. It has been accelerated in the modern day with the expansion of cities and urbanisation, and due to people relocating from rural areas to the city. Switching over to LED lighting was thought to potentially be a way to help with this problem because more efficient lighting means that you need less of them. But actually there's also the reverse argument which is that with more efficient lighting you can get away with having more of it for the same amount of power and so actually you make the problem worse.

How much does light pollution affect professional astronomy?

When we're talking about professional astronomy, a lot of the observations are done from specifically chosen dark sky sites. So we're talking about relatively unpopulated regions of the world, like the Atacama Desert in Chile or the tops of mountainsides in the Canary Islands. The effect of light pollution is not vast in those places because they are so far away from cities in the first place. That's one of the reasons why they've been chosen. That said, not all observatories are placed well away from that and there are issues of light pollution that go beyond just what we're putting up into the sky from the ground. Likewise, there are, of course, issues with increasing numbers of satellites which are contaminating images from professional observatories around the world that while only sort of tangentially related, are nonetheless light pollution issues.

Can light pollution also have an effect on our health?

Absolutely. As humans we are used to being awake during the day and asleep at night. The more light we introduce into our nighttime Skies, the harder it is for our bodies and our body clocks to determine what time it actually is. This leads to insomnia and the issues that come from that - tiredness, fatigue and not to mention also poor mental health. It's not just a human issue either. Wildlife suffers big time from the increase in light pollution, the cycle of predation and prey, for example, has in the past been based on the light of the Moon, because predators need light to be able to hunt by. But of course, if all of the time it is as light as though there were full Moon around, then predators have a constant way of being able to prey on various other animals out there. That can be a serious problem for the diversity and the balance of the biosphere.

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Is there anything we can do to slow this trend down?

Certainly there is a need for careful planning when it comes to the use of lights, specifically street lights and lights in city centres. A lot of it is going to be come down to directional. Of course this lighting is important. No one's denying that the streets need to be lit. The question is whether they need to be lit all the time and in the method that it’s currently being done. Is there a way to be able to have the lights come on at the specific times when they're actually being used by an individual? Is there a way of directing that light downwards? The efficiency of light that goes upwards is useless. It's not helping anyone down on the ground. Anything that increases the efficiency by directing all of that light down onto the ground not only helps with light pollution, but it helps with the specific purpose of those lights in the first place.

Is there anything individuals can do to help with this situation?

Ensure that you're not overusing lights externally. If you have lights in your garden or your driveway or something along those sorts of lines, put them on motion sensors or only have them on at times when you actually want to use them. Also, going for more directional light, light which is being directed downwards rather than upwards or in all directions, can very much improve the amount of light pollution that you are generating.

About our expert, Dr Greg Brown

Greg is an astronomer and science communicator based at the Royal Observatory Greenwich.

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Jason Goodyer
Jason GoodyerCommissioning editor, BBC Science Focus

Jason is the commissioning editor for BBC Science Focus. He holds an MSc in physics and was named Section Editor of the Year by the British Society of Magazine Editors in 2019. He has been reporting on science and technology for more than a decade. During this time, he's walked the tunnels of the Large Hadron Collider, watched Stephen Hawking deliver his Reith Lecture on Black Holes and reported on everything from simulation universes to dancing cockatoos. He looks after the magazine’s and website’s news sections and makes regular appearances on the Instant Genius Podcast.