LIGHT POLLUTION

Brightly illuminated urban areas are increasingly obscuring our view of the night sky, making life difficult for us, astronomers and animals

The brightness of the night sky has been increasing by 7 to 10 per cent a year for the last decade, according to a study carried out by the Globe at Night project. This citizen-science campaign involved more than 50,000 observations from volunteers around the world.

The problem, according to the report, is ‘skyglow’ – artificial light that keeps the sky in twilight until long after the Sun has set.

We spoke to Dr Greg Brown, an astronomer based at the Royal Observatory Greenwich, about what this trend means for laypeople, astronomers and the natural world, and if there’s anything we can do to reverse it.

HOW BAD IS THE LIGHT POLLUTION SITUATION? ARE WE LOOKING AT A POTENTIAL SCENARIO WHERE FUTURE GENERATIONS WON’T BE ABLE TO ENJOY LOOKING AT THE STARS?

It’s a great shame that a lot of people are denied a view of the night sky. In the planetarium that we run at the Royal Observatory, we often start our shows with an estimate of the current light pollution around London. Even in our relatively dark site in the middle of Greenwich Park, we still have to deal with Canary Wharf and the main parts of the city around us.

When we compare what we can see to what the night sky would look like from a dark-sky site, the difference is massive. There’s absolutely no doubt that light pollution is 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 – the array of stars in the Milky Way, for example – are already basically impossible to see from suburban areas, let alone city centres. So, yes, light pollution is very much hampering the ability of the average person to be able to explore the cosmos.

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 light. This is a problem, as modern light pollution tends to be blue light since we started replacing sodium lamps with LEDs in street lighting. So a lot of studies nowadays have to be done from the ground in order to make up for that. That’s where the citizen science angle comes from in the Globe at Night project. There simply aren’t enough scientists 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 1970s. It has been accelerated by the expansion of cities and urban areas, as people have relocated from rural areas. It was thought that switching over to LED light would potentially be a way to help with the problem, because more efficient lighting means that you need fewer lights. But there’s also the reverse argument, which is that more efficient lighting means you can get away with having more lights for the same amount of power, 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, such as the Atacama Desert in Chile or mountains in the Canary Islands. The effect of light pollution is not so big in those places because they’re so far away from cities. That’s one of the reasons why they’ve been chosen.

That said, not all observatories are placed well away from sources of light pollution and there are issues that go beyond the light that we’re putting up into the sky from the ground.

Likewise, there are, of course, issues with the increasing number of satellites that are contaminating images captured by professional observatories around the world, which, while only

tangentially related, are nonetheless light-pollution issues.

CAN LIGHT POLLUTION HAVE AN EFFECT ON OUR HEALTH?

Absolutely. As humans we’re used to being awake during the day and asleep at night. The more light we introduce into our night-time 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 poor mental health. [For more on the health problems associated with disrupted sleep, turn to p66.]

It’s not just a human issue either. Wildlife suffers a great deal 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 most predators need light to be able to hunt. But if every night is as lit up as though there were a full Moon, then predators can constantly prey on the various other animals out there. That can be a serious problem for the diversity and balance of the biosphere.

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 come down to where the light is directed. Of course, 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 way they’re currently being lit. Is there a way to be able to have the lights come on at specific times, such as when they’re actually needed by an individual nearby? Is there a way of directing more, or all, of that light downwards, as the light that’s going upwards is useless – it’s not helping anyone down on the ground.

Anything that increases street lamps’ efficiency by directing all of that light down onto the ground not only helps with light pollution, but it also helps fulfil 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, hook them up to motion sensors or only have them on at times when you actually need them. Also, going for more directional light – light that’s being directed downwards rather than upwards or in every direction – can very much reduce the amount of light pollution that you’re generating.