Star light, star bright, last star I see tonight

Although you might not have noticed, our skies are changing at astronomical speeds.

A combination of light pollution on the ground and more satellites and debris in the sky means astronomers are slowly running out of truly dark places to study the stars.

Researchers have created a new method for simulating night sky brightness, and the results show that we’re even worse than we thought.

“Although first recognised decades ago, light pollution only recently emerged as being among the most pressing environmental challenges due to its many negative influences on astronomy,” the researchers write in Nature Astronomy.

“Excessive light emissions from a growing number of artificial sources are making ground-based astronomical observations progressively more difficult or even impossible in many parts of the world.”

The team from Slovakia highlighted a type of modelling that uses a theory of light scattering called ‘Mie scattering’, however the researchers found that this simple theory can produce significant underestimates – particularly at low altitudes.

The issue is that although someone could be in a completely dark area, dust, satellites or debris in the sky can reflect other artificially lit areas (or the sun once it’s below the horizon) and provide ‘skyglow’.

Satellites and debris are becoming much more common in low earth orbit with thousands of satellites now circling around Earth. This is good for worldwide internet but provides headaches for both radio and visual astronomers.

Read more: Should Australia be using satellites to keep coal companies honest?

Two accompanying editorials in Nature Astronomy – a Perspective and Comment – are much tougher on satellites.

“Every time some health or environmental issue arises and starts to be addressed in the scientific literature, the ‘machine of doubt’ is put into action by the polluters to stop, or at least delay by years or decades, the adoption of countermeasures and rules to protect human health and the environment,” a group of European researchers wrote in the accompanying Comment.

“Regarding the impacts of Low Earth Orbit satellites on the night sky and science, it is similarly naive to hope that the skyrocketing space economy will limit itself, if not forced to do so, to counter the new environmental and security issues raised by the new mega-constellations of satellites.”

Last month, researchers and scientists went to the UN Committee on the Peaceful Uses of Outer Space to discuss how to keep our skies ‘dark’ and ‘quiet’.  These processes have not yet provided solutions to the satellites vs astronomers debate, however an article by University of San Francisco physicist Professor Aparna Venkatesan – also in Nature Astronomy – suggests that the best way forward are global policies to regulate the satellites and provide mitigation.

“Without coordinated global regulation and oversight, clear international protocols for orbital traffic management, or minimal standards for environmental impacts, the wide-ranging consequences for astronomers and for humanity are an ongoing endeavour of low Earth orbit whack-a-mole tinged with roulette,” she writes. 

“We are left with the growing unease of watching the slow-motion inevitability of a preventable disaster in low Earth orbit.” The research has been published in Nature Astronomy.

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