A new study has revealed that a remote site in Antarctica is the best place on Earth for stargazing without atmospheric disturbance.
On a remote polar plateau in Antarctica, 4000 metres above sea-level, atop an eight metre high tower, sits a telescope with the best view of space on Earth. Dome A, as its known, holds the most undisturbed view of the night sky on Earth, researchers have found.
The team of international scientists included researchers from the University of New South Wales (UNSW). They published their findings in the prestigious journal Nature this week.
The conditions at Dome A are so clear that the stars don’t even twinkle.
Why do stars twinkle?
Stars in the night sky often seem to twinkle and wobble. This is a consequence of the atmosphere we are viewing the stars through.
When light from distant stars enters the atmosphere it has to travel through a lengthy 100 kilometres of air before reaching our eyes. This is the height of the Kármán Line, the altitude where space is thought to begin.
Earth’s atmosphere is rich with varying air temperatures, capable of bending and contorting light. This same effect can be seen on hot days, when hot air rising from the ground can bend light rays to create a displaced image of distant objects. This phenomenon is known as a mirage.
Hot air in the sky swirls and mixes with the cold air around it, creating atmospheric turbulence. As the light from distant stars travels through this turbulence, it too is bent and wobbled. This leads to the distinctive twinkle we are used to seeing.
The closer a star is to the horizon, the more it twinkles. This is because there is more atmosphere for the light to travel through before reaching our eyes, hence more turbulence.
Finding the perfect stargazing spot
Location Location Location
The spot where Dome A sits has an extremely stable atmosphere, meaning that the risk of atmospheric turbulence is minimal. This is due to its location being situated on flat land for hundreds of kilometres in every direction. Also, its 4000-metre altitude above sea level contributes to its atmospheric stability.
“There is this very slow wind that blows across the plateau which is so smooth that it doesn’t generate much turbulence,” says Professor Michael Ashley, who helped design and build the telescope system at Dome A.
“What little turbulence there is we see restricted to a very low ‘boundary layer’ – the area between the ice and the rest of the atmosphere.”
“We measured the boundary layer thickness at Dome A using a radar technique about a decade ago and it’s about 14 meters, on average, but it fluctuates – it goes down to almost nothing, and it goes up to maybe 30 metres.” By setting the telescope atop an eight metre platform, this boundary layer was overcome around a third of the time.
All Night Long (All Night)
Dome A lies just 900 kilometres from the South Pole. This means that during mid-winter it can be plunged into darkness for over 24 hours at a time. This allows for a much longer window of time for stargazing.
“If you were to observe a star in say, Sydney, from when it rises to when it sets, you can only observe it for maybe eight hours a night,” Prof Ashley explained.
“Whereas in wintertime at Dome A you can observe a star continuously. And for some projects like searching for planets around other stars, the fact that you can observe them continuously means you can find planets around them much more effectively.”
Proving stargazing potential
In order to demonstrate Dome A’s astronomical prowess, a test of its photo-taking quality needed to be undertaken. Between 11th April and 4th August 2019, the telescope took one photo every minute. This equated to 45,930 images taken when the boundary layer was below the tower.
These images were taken remotely, as Professor Ashley explained. “It was very difficult because the observations have to be made in mid-winter with no humans present. UNSW played a crucial role in designing and building the infrastructure that was used – the power supply system, computers, satellite communications – which was managed by remote control.”
After a long analysis of the photos, Dome A’s image clarity was undeniable. The twinkling of the stars was “greatly reduced” and star images were found to be “much sharper and brighter” than anywhere else.
Looking ahead, and up
As research continues, Professor Ashley hopes that Australia will grow to recognise Dome’s A great potential in space research.
“Dome A is a superb site for astronomical observations, and we should make every effort to participate in an international project to put a large telescope there to take advantage of the conditions.”
“With Antarctica being so close to Australia, it is a tremendous opportunity.”
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