Scientists looking for site for giant solar telescope

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Chinese scientists are looking for a site for a giant solar telescope, which will be the world's largest in the next two decades with data helping to understand solar activities.

The Chinese Giant Solar Telescope (CGST), or one of "the next-generation ground-based solar telescopes," will lead a field of solar observation in 20 years, if the construction is approved and starts in 2016, according to Prof. Deng Yuanyong, director of Huairou Solar Observing Station of the National Astronomical Observatories (NAO) under the Chinese Academy of Sciences (CAS).

The national project with a budget of about 90-million U.S. dollars was proposed by the entire solar community of China.

It aims to build a very large infrared and optical solar telescope, with the spatial resolution expected to be equivalent to an 8meter-diameter telescope and light-gathering power equivalent to a 5m-diameter full aperture telescope, Deng told Xinhua at the International Astronomical Union (IAU)'s 28th General Assembly, which started in Beijing on Aug. 21 and will last two weeks.

The world's largest ground-based solar telescope currently in use is the 1m solar telescope of Sweden, with solar telescopes of 1.5m and 1.6m soon to be launched by Germany and the United States, respectively.

Deng, an initiator of the project, said the CGST will obtain precise measurements of the solar vector magnetic field with high-spatial resolution, and detect the fine structures of solar magnetic field and dynamic field.

The elemental magnetic structures play a key role in the process of all kinds of solar magnetic interactions. However, after more than 100 years of development, the nature of the solar magnetic field is still one of the most important mysteries in solar physics.

According to Deng, the CGST will surpass the capabilities of the large optical telescopes currently being planned by other countries, such as the U.S. Advanced Technology Solar Telescope (ATST), which is going to be installed in Hawaii, and the European Solar Telescope (EST). Both have a design diameter of 4m.

"From 1m and 8m and the preferred adoption of the ring structure as it has superiority in the thermal design, scientists have to conquer many key technologies," Deng said, adding the construction period is expected 10 to 15 years.

"Although solar physics has made big progress with ground-based and space-borne observations in the past decades, it seems that we do need more efforts," he continued.

He also said the detection of the fundamental structure of the magnetic field always requires resolution -- spatial, temporal, and spectral -- and sensitivity as high as possible.

As solar radiation in the infrared region is very weak, gathering more photons with a larger telescope is necessary, which is not only required for high resolution but also for the high magnetic sensitivity, Deng said.

"The results of simulation and analysis showed that the current design could meet the demand of most science cases not only in infrared band but also in near infrared band and even in visible band," he said.

At present, the best site in China for solar observations was found in Fuxian Lake of Yunnan Observatory in southwest China. "However, as the CGST will mainly work in the infrared, this site is not ideal," Deng said.

In 2010, the Chinese solar community started a four-year project called "site survey for solar observations in the western part of China," which was supported by the National Science Foundation of China to find the best site for the CGST and other solar projects.

Lin Jun, chief scientist of the CAS Yunnan Observatory, said the western part of the country, including Tibet Autonomous Region as well as Yunnan and Sichuan provinces, may provide more candidates for the site of the CGST with the right geological and weather conditions.

"The site must stay far away from the hustle and bustle of cities, as well as modern industrialization," Lin said, adding the telescope could also monitor the solar energy and the change of the local environment.

The CGST was selected and recommended by the CAS to the National Development and Reform Commission (NDRC), China's economic planner that approved major infrastructure projects, as the "National major basic scientific project for 2016-2030" in January 2010.

In November that year, the CGST was selected by the NDRC as a National 14-15th Five-Year planning project for astronomy (2021-2025, or 2026-2030).The long-term astronomical project was proposed in 2009 by the NAO, Yunnan Observatory, Purple Mountain Observatory in Nanjing, Nanjing University, Nanjing Institute of Astronomical Optical Technology and Beijing Normal University, which are the six major solar research groups in China.

"As the CGST is still in its very early stage, we are looking forward to more international collaboration," Deng said.

Meanwhile, some large-scale astronomical projects in China, including the Large Sky Multi-Object Fiber Spectroscopic Telescope (LAMOST) completed in 2008 in Xinglong, north China's Hebei Province, and the 500m Aperture Spherical Radio Telescope (FAST) to be completed in 2016 in Pingtang County of southwestern Guizhou Province, will provide experience for the building of the CGST.

There are also more ambitious plans for China to build telescopes in space. "We are planning both ground-based and space solar telescopes," Deng said, adding China is planning to launch the Space Solar Telescope (SST) project, which was first proposed in mid-1990s.

A 1m optical telescope equipped with a two-dimensional real-time spectrograph and high-accuracy polarimeter will be sent into space to observe the basic structures and understand the solar magnetic field, he said.

The 1m-diameter Chinese SST will surpass the 0.5m space telescope of the Japanese Hinode solar mission launched in 2006 with the collaboration of the United States and Britain, Deng said.

"Astronomical observation through space telescopes avoids disturbance from the earth's atmosphere," said Lin Jun.

However, due to the difficulty and risks of space missions, working from the ground is a better way to develop the technology and the approach to use later for space mission, he said.

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