Astronomer Carl Sagan famously said that there were more stars in the universe than grains of sand on earth.
It has been estimated that there are over 100 billion stars in the Milky Way galaxy. While there is a limit to how many stars we can see from earth with the naked eye, that number is dramatically reducing due to light pollution.
“We should be able to see around 2500 stars with the naked eye on any night, and we can see about 125 of them at best in Sydney,” says astrophysicist, proud Wiradjuri woman and UNSW PhD candidate Ms Kirsten Banks.
In fact, in a recent study published in Science, data collected by citizen scientists around the world found light pollution is increasing at a rate that is equivalent to the brightness of the sky doubling every eight years.
This latest research continues to expose the extent to which we’re losing the darkness of our night sky. Not being able to look up and see the stars will have significant cultural impacts, but there are steps we can all be taking to reduce the effect of light pollution.
What causes 'light glow'?
Artificial lighting that escapes and seeps into the sky causes what is known as “light glow” – a form of light pollution that stops humans from seeing the stars.
“Light glow is this extra light that is not actually useful for seeing when you're walking in the dark, for example. And it's this glow of light that spreads out and leaks into the sky in a way that washes out fainter lights that are usually stars,” says Ms Banks.
This latest study involved over 51,000 citizen science observations of stellar visibility with the naked eye, revealing the change in global sky brightness over an 11-year period – from 2011 to 2022.
The data showed that the number of visible stars decreased by an amount that can be explained by an increase in sky brightness of seven to 10 per cent per year.
This study was done on a global scale, but around 68 per cent of the observations were from North America and Europe, with a one-off campaign in Australia in 2020, and a scattering of data collected across Asia, Africa and South America.
Although the data was primarily collated from elsewhere, Ms Banks explains that light pollution is still a problem in Australia. “In Sydney, the light pollution that we experience is almost the same light pollution as the moon emits. This means if you're in a place with no light pollution, and there's a full moon out, you have the same sort of night sky visibility that you would in Sydney.”
Everyone is an astronomer
You don’t need any fancy machinery or special equipment to observe the stars.
“I think it's important for everyone to be able to look up into the stars, because it's one of the most accessible sciences out there,” says Ms Banks. “All you need to do is look up and you can see it, you are doing astronomy by looking up into the night sky. And when we take that away with light pollution, that takes a whole science away from people.”
Many different cultures around the world have a rich history and connection to the stars and the night sky.
In Australia alone, there are over 250 Indigenous groups that have understood and used the stars for the last 65,000 years, and their knowledge is still exercised to this day, says Ms Banks.
Ms Banks speaks about Gugurmin, the Celestial Emu – a constellation based on the dark space around the Milky Way – in her 2019 TEDx talk on the great history of Australian Aboriginal Astronomy.
“The night sky is really important to Aboriginal peoples.
“We're losing culture because of the stars we're losing sight of in these bright cities. All of these stars have cultural importance within stories and lessons. And some of them we just can't see anymore. So through that, and, of course, all of the other effects of colonisation, we're losing all those stories.”
Reversing the impact of light glow
Unlike many other forms of pollution, light pollution is reversible and there are measures we can take to restore the deep darkness of the sky.
“There are lots of ways to reduce the amount of light pollution that we put out into the sky,” says Ms Banks.
“One good example is by creating very directional streetlights. So, when you walk around, you may see some streetlights that are just these big lights that shine in all directions. But really, you only need light to shine down on the path that you're walking on, because that's where it's actually useful. So we can change the design of our lights to be more proactive about where we actually want the light to be.”
As well as the direction and brightness of the lights we use, we can also change the colour to a more amber/orange hue which reduces light glow, explains Ms Banks.
While some of these measures have been adopted on a local scale, there is lots more that can be done. In recent years, awareness of light pollution has led some policymakers to introduce measures that attempt to control it.
“These measures have already been taken in places like Coonabarabran,” says Ms Banks. “There are very strict guidelines for all sorts of lights and they have certain regulations so that they preserve the night sky for that area, because of the observatory nearby.”
As Ms Banks explains, everyone can have a part to play. “One way that people can get involved is just turning off lights that are unnecessary, like really bright floodlights on your backyard or your patio.
“There are simple solutions to this that people can take every single day.”