Home / Science / The best place on Earth to see the stars – where they can finally be seen without their twinkle

The best place on Earth to see the stars – where they can finally be seen without their twinkle

South Pole telescope

The South Pole Telescope at the South Pole station of the United States Amundsen-Scott, with a brilliant sunrise in July 2020. Credit: Geoff Chen

Stars seen from a place called Cupola A in Antarctica can finally be seen without their glint, which means in much more detail.

Have you ever wondered why the stars shine? It is because the turbulence in the Earth̵

7;s atmosphere causes the light emitted by the star to falter as it completes its journey along light years towards the lenses in our eyes and in our telescopes.

But now scientists from international research institutions including UNSW Sydney have found the best place on Earth where – with the help of technology – we can see distant stars as they really appear, without the distorted glint.

And it happens that it is located south of Davis station in Australia, in Antarctica, on a plateau at 4000 meters above sea level called Dome A.

Dome on the map of Antarctica A

A map of Antarctica showing the dome A, which is 900 km from the South Pole. Credit: Xiaoping Pang and Shiyun Wang, Chinese Antarctic Detection and Mapping Center

In research published today in the journal Nature, the scientists showed that the conditions on the plateau lend themselves perfectly to the vision of stars from Earth with interference significantly reduced by atmospheric turbulence.

According to Professor Michael Ashley of UNSW Science, who was part of the China-led group of researchers who designed, built and created a small telescope system at dome A, the results represent a fantastic opportunity to get better observations of the universe from the ground telescopes based.

“After a decade of indirect evidence and theoretical reasoning, we finally have direct observational evidence of the extraordinary conditions of dome A,” says Professor Ashley, an astronomer at the UNSW School of Physics.

“Dome A is the highest point in the central highland region of Antarctica and the atmosphere is extremely stable here, far more than anywhere else on Earth. The result is that the beat of the stars is significantly reduced and the images of the stars are much sharper and brighter. “

KunLun Differential Image Motion Monitor 8M Tower

The KunLun Differential Image Motion Monitor on top of the 8 meter high tower. Credit: Zhaohui Shang

The telescope installed on Dome A – the KunLun differential image movement monitor – had an opening of 25 cm and placed on an eight-meter platform. The height of the platform was crucial because it raised the telescope above the steep temperature gradients near the ice.

As Professor Ashley explains, turbulent eddies build up when the wind moves over a changing topography like mountains, hills and valleys.

“This causes the atmospheric turbulence that bends the star light, so when it hits the ground, it’s everywhere and you get these blurry images.”

Boundary layers

But, he says, Cupola A in Antarctica is a plateau that is almost completely flat for many hundreds of kilometers in every direction, making its atmosphere very stable. It is also at an altitude of over 4000 meters, much higher than Mount Kosciuszko.

KunLun Differential Image Motion Monitor Tower

The telescopes were positioned on an 8-meter tower that allowed the stars to be seen without distortion when the boundary layers of the atmosphere dropped to a height less than this height, about a third of the time. Credit: Zhaohui Shang

“There is this very slow wind blowing across the plateau that is so regular that it doesn’t generate much turbulence,” says Professor Ashley.

“What little turbulence there is we see limited to a very low” boundary layer “- the area between the ice and the rest of the atmosphere.

“We measured the thickness of the boundary layer at Dome A using a radar technique about a decade ago and on average it’s about 14 meters, but it fluctuates – it drops to almost nothing and reaches maybe 30 meters.”

The team found that by installing the telescope on an 8-meter platform, it protruded beyond the boundary layer about a third of the time. Last year, between 11 April and 4 August, the telescope took photos every minute and obtained 45,930 images taken when the boundary layer was less than the 8-meter platform, as reported in Nature.

Professor Ashley says it was very difficult to finally get the readings and images that confirmed Dome A as the main location on earth to see in the depths of the cosmos.

“It was very difficult because the observations must be made in mid-winter without the presence of humans. UNSW played a crucial role in the design and construction of the infrastructure that was used – the power system, computers, satellite communications – which was managed by remote control. “

Terrestrial and satellite telescopes

But if the atmosphere were so devastating with our instruments on Earth, wouldn’t a satellite – like the Hubble telescope launched in 1990 – be ideal for such a job?

The professor. Ashley says there are a couple of good reasons why a terrestrial telescope installed on dome A would be the best option. In addition to the obvious dollar savings, there are also savings over time.

“Satellites are much more expensive,” says Professor Ashley, “we are perhaps talking about factors 10 to 100 times the cost. But another advantage of making Earth-based observations is that you can always add the latest technology to your telescope. on the ground. While in space, everything is late. And you can’t easily use many modern integrated circuits because they are not hardened by radiation. So you end up with the space that slows down technology on the ground for at least 10 years. “

KunLun Differential Image Movement Monitor

The telescopes and towers were designed and built by Chinese researchers who led the study. Credit: Zhaohui Shang

Another advantage of using a telescope in Dome A rather than anywhere else on the planet is that smaller and weaker stars are suddenly much more observable thanks to better resolution.

“Basically this means that for a given size telescope, you will get a much better image on Dome A. So instead of building a large telescope on a non-Antarctic site, you could build a smaller one and get the same performance, so it’s cheaper. “

Polar nights

There is also a strategic advantage in the position of Cupola A – which is 900 km from the South Pole – compared to other areas of the Earth at more hospitable latitudes. Being so far from the equator, the polar nights of 24 hours or more of darkness in mid-winter open a much wider window to see the stars.

“If you were to observe a star, for example, Sydney, from when it rises to when it sets, you can only observe it for perhaps eight hours a night,” says Professor Ashley.

South Pole telescope

The South Pole Telescope at the South Pole station of the United States Amundsen-Scott, with a brilliant sunrise in July 2020. Credit: Geoff Chen

“While in winter at Cupola A you can continuously observe a star. And for some projects like finding planets around other stars, the fact that you can continuously observe them means that you can find planets around them much more effectively. “

Looking to the future, prof. Ashley says she would like to continue research with UNW’s Chinese partners, and notes that China has an impressive and growing record in Antarctic scientific research. But he wonders if Australia recognizes the great potential that dome A represents in space research.

“Dome A is an exceptional 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 so close to Australia, it’s an extraordinary opportunity,” he says.

Reference: Bin Ma, Zhaohui Shang, Yi Hu, Keliang Hu, Yongjiang Wang, Xu Yang, Michael C. B. Ashley, Paul Hickson & Peng Jiang, 29 July 2020, “Night measurements of astronomical seeing in dome A in Antarctica” Nature.
DOI: 10.1038 / s41586-020-2489-0

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