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May 16, 2019

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Riding a wave of success

The Tianma Telescope, which is as large as eight basketball courts, with a diameter of 65 meters and a height of 70 meters, stands in the fields at the foot of Sheshan Hill in Songjiang District.

It now ranks No. 1 in Asia and No. 3 in the world in terms of overall performance, after the 110-meter-diameter Green Bank Telescope in the US and the 100-meter-diameter Effelsberg Telescope in Germany.

The Tianma can pick up eight different frequency bands, making it powerful enough to observe celestial bodies more than 10 billion light years away.

“If you are on Mars, you can pick up phone calls from Earth,” said Shen Zhiqiang, head of the Shanghai Astronomical Observatory under the Chinese Academy of Sciences.

The Tianma has been used in a number of crucial astronomical missions since it began operation in 2012. It has detected radio bursts from a magnetar, a type of neutron star, near the supermassive black hole in the galactic center. Currently, there are only four magnetars that have been detected by radio emissions.

The radio telescope’s first mission was to track and position the Chang’e-2 lunar probe in December 2012, as part of China’s Very Long Baseline Interferometry system, which is used by scientists around the world to track moving objects in the universe.

The system comprises a data center in Shanghai and telescopes in Shanghai, Beijing, Kunming and Urumqi that form one giant “telescope” with a diameter of more than 3,000 kilometers.

Later, the Tianma joined the Chang’e-3 and 4 probes.

This year, it will be contributing to the Chang’e-5 probe, and will participate in China’s first Mars probe in 2020 and the Jupiter probe in 2025, according to Shen.

Construction on the Tianma site started in March 2010 and it was completed in October 2012.

“Usually, it takes six years to complete such a large-scale facility,” Shen said, noting the challenges surmounted by local engineers and scientists.

As a fully steerable radio telescope, Tianma can move in every direction above the horizon, offering a 360-degree panorama of the universe with a “best pointing” accuracy of 3 arc seconds — equal to 1/7,200 degrees of every tick of a watch second hand.

The telescope weighs about 2,700 tons and, according to Shen, is in operation about 7,000 hours every year.

The radio telescope was a “serendipity discovery,” said Shen.

In 1931, American radio engineer Karl Jansky discovered radio waves emanating from the Milky Way in an experiment designed to study static electricity disturbances in radio telephone services.

For the first time, humans listened to the universe, Shen said.

Jansky’s discovery, publicized in 1931, inspired the invention of the radio telescope. Unlike optical telescopes that receive visible light, the radio telescope picks up radio emissions from the universe.

Then, scientists process the data and draw sky maps.

Many celestial bodies, such as black holes in the center of the Milky Way and rapidly rotating stars, are only “visible” in the radio frequency portion of the electromagnetic spectrum.

“We could normally just see one of a trillion of photons from the center of the Milky Way,” Shen said.

“By using a radio telescope, we can ‘see’ many of them.

“Just last month, humans saw the first-ever close-up of a black hole, captured by the Event Horizon Telescope, a network of several radio telescopes scattered across the globe.”




 

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