View source for Astronomy:Five-hundred-meter Aperture Spherical Telescope

{{short description|Radio telescope located in Guizhou Province, China}}
{{EngvarB|date=July 2019}}
{{Infobox telescope}}

The '''Five-hundred-meter Aperture Spherical Telescope''' ('''FAST'''; {{zh|s=五百米口径球面射电望远镜}}), nicknamed '''Tianyan''' ({{lang|zh-Hans|天眼}}, lit. "Sky's/Heaven's Eye"), is a [[Astronomy:Radio telescope|radio telescope]] located in the Dawodang depression ({{lang|zh-Hans|大窝凼洼地}}), a natural basin in Pingtang County, Guizhou, southwest China.<ref>{{cite web |title=<span lang="zh-Hans">中国"天眼"能不能发现外星人？</span> |language=zh |trans-title=Can Chinese Tianyan find aliens? |date=22 February 2016 |publisher=Xinhua News Agency |url=http://news.xinhuanet.com/world/2016-02/22/c_128741240.htm |access-date=27 February 2016 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304193815/http://news.xinhuanet.com/world/2016-02/22/c_128741240.htm |url-status=live }}</ref> FAST has a {{cvt|500|m}} diameter dish constructed in a natural depression in the landscape. It is the world's largest filled-aperture radio telescope<ref name="Brinks">{{cite web |last=Brinks |first=Elias |title=China Opens the Aperture to the Cosmos |work=The Conversation |publisher=U.S. News & World Report |date=11 July 2016 |url=https://www.usnews.com/news/best-countries/articles/2016-07-11/china-builds-worlds-largest-radio-telescope |access-date=12 August 2016 |archive-date=26 August 2016 |archive-url=https://web.archive.org/web/20160826032054/http://www.usnews.com/news/best-countries/articles/2016-07-11/china-builds-worlds-largest-radio-telescope |url-status=live }}</ref> and the second-largest single-dish aperture, after the sparsely-filled [[Astronomy:RATAN-600|RATAN-600]] in Russia.<ref name="Nan 2009">{{cite conference |url=http://159.226.88.6/sinous2008/talks/21Apr/NanRendong.pdf |title=Project FAST – Five hundred meter Aperture Spherical radio Telescope |last=Nan |first=Rendong |date=April 2008 |location=Beijing |conference=China-US Bilateral Workshop on Astronomy |conference-url=http://159.226.88.6/sinous2008/ |access-date=4 July 2016 |archive-date=7 August 2016 |archive-url=https://web.archive.org/web/20160807121205/http://159.226.88.6/sinous2008/talks/21Apr/NanRendong.pdf |url-status=live }}</ref><ref name="NewSci 2011">{{cite news |url=https://www.newscientist.com/article/mg21028165-300-china-starts-building-worlds-biggest-radio-telescope/ |title=China starts building world's biggest radio telescope |work=New Scientist |date=8 June 2011 |access-date=19 October 2015 |archive-date=8 December 2015 |archive-url=https://web.archive.org/web/20151208155313/https://www.newscientist.com/article/mg21028165-300-china-starts-building-worlds-biggest-radio-telescope/ |url-status=live }}</ref>

It has a novel design, using an [[Astronomy:Active surface|active surface]] made of 4,500 metal panels which form a moving parabola shape in real time.{{r|Normile}} The cabin containing the [[Engineering:Antenna feed|feed antenna]], suspended on cables above the dish, can move automatically by using winches to steer the instrument to receive signals from different directions. It observes at wavelengths of 10&nbsp;cm to 4.3&nbsp;m.<ref name=Nan11>{{cite journal |first=RENDONG |last=NAN |title=The Five-Hundred-Meter Aperture Spherical Radio Telescope (Fast) Project |institution=Key Laboratory for Radio Astronomy, Chinese Academy of Sciences |journal=International Journal of Modern Physics D |volume=20 |issue=6 |pages=989–1024 |date=2011 |doi=10.1142/S0218271811019335 |url=https://doi.org/10.1142/S0218271811019335 |bibcode=2011IJMPD..20..989N |arxiv=1105.3794 |s2cid=26433223 |access-date=25 January 2021 |archive-date=15 June 2022 |archive-url=https://web.archive.org/web/20220615184329/https://www.worldscientific.com/doi/abs/10.1142/S0218271811019335 |url-status=live }}</ref><ref name=Li18>{{cite journal |title=FAST in Space: Considerations for a Multibeam, Multipurpose Survey Using China's 500-m Aperture Spherical Radio Telescope (FAST) |first=Di |last=Li |institution=National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China |journal=IEEE Microwave Magazine |volume=19 |issue=3 |pages=112–119 |date=2018 |doi=10.1109/MMM.2018.2802178 |url=https://ui.adsabs.harvard.edu/abs/2018IMMag..19..112L/abstract |arxiv=1802.03709 |bibcode=2018IMMag..19..112L |s2cid=4595986 |access-date=25 January 2021 |archive-date=4 May 2022 |archive-url=https://web.archive.org/web/20220504005815/https://ui.adsabs.harvard.edu/abs/2018IMMag..19..112L/abstract |url-status=live }}</ref>

Construction of FAST began in 2011. It observed [[Astronomy:First light|first light]] in September 2016.<ref name=firstlight>{{cite news |title=Xi commends launch of world's largest radio telescope in China |author=Xinhua |via=China Daily |date=25 September 2016 |url=http://www.chinadaily.com.cn/china/2016-09/25/content_26891108.htm |access-date=10 October 2017 |archive-date=11 October 2017 |archive-url=https://web.archive.org/web/20171011021808/http://www.chinadaily.com.cn/china/2016-09/25/content_26891108.htm |url-status=live }}</ref> After three years of testing and commissioning,<ref name="FAST">{{cite web |url=http://fast.bao.ac.cn/en/FAST.html |title=FAST Homepage in English |access-date=15 January 2017 |archive-url=https://web.archive.org/web/20170316160050/http://fast.bao.ac.cn/en/FAST.html |archive-date=16 March 2017 |url-status=dead}}</ref> it was declared fully operational on 11 January 2020.<ref>{{cite web |url=http://www.xinhuanet.com/english/2020-01/11/c_138696939.htm |title=World's largest radio telescope starts formal operation |website=Xinhua |date=11 January 2020 |access-date=13 January 2020 |archive-date=13 January 2020 |archive-url=https://web.archive.org/web/20200113001446/http://www.xinhuanet.com/english/2020-01/11/c_138696939.htm |url-status=dead }}</ref>

The telescope made its first discovery, of two new [[Astronomy:Pulsar|pulsar]]s, in August 2017.<ref>{{cite news |title=China's huge new FAST radio telescope discovers two new pulsars |first=Andrew |last=Jones |date=10 October 2017 |publisher=GBTimes |url=https://gbtimes.com/chinas-huge-new-fast-radio-telescope-discovers-two-new-pulsars |access-date=10 October 2017 |archive-date=11 October 2017 |archive-url=https://web.archive.org/web/20171011181434/https://gbtimes.com/chinas-huge-new-fast-radio-telescope-discovers-two-new-pulsars |url-status=live }}</ref> The new pulsars PSR J1859-01 and PSR J1931-02—also referred to as FAST pulsar #1 and #2 (FP1 and FP2), were detected on 22 and 25 August 2017; they are 16,000 and 4,100 light years away, respectively. [[Astronomy:Parkes Observatory|Parkes Observatory]] in Australia independently confirmed the discoveries on 10 September 2017. By September 2018, FAST had discovered 44 new pulsars,<ref>{{cite web |last1=McGlaun |first1=Shane |title=Chinese FAST telescope finds multiple pulsars in early use |url=https://www.slashgear.com/chinese-fast-telescope-finds-multiple-pulsars-in-early-use-11503525/ |website=slashgear |access-date=11 October 2017 |date=11 October 2017 |archive-date=11 October 2017 |archive-url=https://web.archive.org/web/20171011172438/https://www.slashgear.com/chinese-fast-telescope-finds-multiple-pulsars-in-early-use-11503525/ |url-status=live }}</ref><ref>{{cite web |last1=Jones |first1=Andrew |title=China's FAST radio telescope detects three more pulsars |url=https://gbtimes.com/chinas-fast-radio-telescope-detects-three-more-pulsars?cat=chinese-martial-healing-arts |website=gbtimes |access-date=14 December 2017 |archive-date=17 September 2018 |archive-url=https://web.archive.org/web/20180917110650/https://gbtimes.com/chinas-fast-radio-telescope-detects-three-more-pulsars?cat=chinese-martial-healing-arts |url-status=live }}</ref><ref>{{cite news |title=China's FAST telescope identifies 44 pulsars |url=http://english.scio.gov.cn/chinaprojects/2018-09/12/content_63384697.htm |access-date=12 September 2018 |work=scio.gov.cn |archive-date=17 September 2018 |archive-url=https://web.archive.org/web/20180917071445/http://english.scio.gov.cn/chinaprojects/2018-09/12/content_63384697.htm |url-status=live }}</ref> and by 2021, 500.<ref>{{Cite web |url=http://en.people.cn/n3/2021/1216/c90000-9933484.html |title=China's FAST telescope detects over 500 new pulsars - People's Daily Online |access-date=16 December 2021 |archive-date=16 December 2021 |archive-url=https://web.archive.org/web/20211216043734/http://en.people.cn/n3/2021/1216/c90000-9933484.html |url-status=live }}</ref>

==History==
[[File:FAST under construction, took from rim..jpg|left|thumb|upright|FAST under construction]]

The telescope was first proposed in 1994. The project was approved by the [[Finance:National Development and Reform Commission|National Development and Reform Commission]] (NDRC) in July 2007.{{sfn|Jin|Nan|Gan|2007}} A 65-person village was relocated from the valley to make room for the telescope{{r|Xinhua complete}} and an additional 9,110 people living within a {{cvt|5|km|mi|sigfig=1}} radius of the telescope were relocated to create a radio-quiet area.<ref name="Xinhua complete">{{Cite news |title=Xinhua Insight: Installation complete on world's largest radio telescope |url=http://news.xinhuanet.com/english/2016-07/03/c_135485389.htm |date=3 July 2016 |journal=Xinhua |access-date=4 July 2016 |archive-date=3 July 2016 |archive-url=https://web.archive.org/web/20160703113734/http://news.xinhuanet.com/english/2016-07/03/c_135485389.htm |url-status=dead }}</ref> The Chinese government spent around {{US$|269 million}} in poverty relief funds and bank loans for the relocation of the local residents, while the construction of the telescope itself cost $180 million.<ref>{{cite news |title=The Quest For Life Beyond Earth: The World's Largest Radio Telescope Just Went Online |first1=Cecille |last1=De Jesus |editor-first=Patrick |editor-last=Caughill |date=26 September 2016 |journal=Futurism |url=https://futurism.com/the-quest-for-life-beyond-earth-the-worlds-largest-radio-telescope-just-went-online/ |access-date=19 February 2017 |archive-date=12 April 2019 |archive-url=https://web.archive.org/web/20190412034819/https://futurism.com/the-quest-for-life-beyond-earth-the-worlds-largest-radio-telescope-just-went-online |url-status=live }}</ref>

On 26 December 2008, a foundation-laying ceremony was held on the construction site.<ref>{{cite web |url=http://gzrb.gog.com.cn/system/2008/12/27/010441147.shtml |title=<span lang="zh-Hans">中国科学院·贵州省共建国家重大科技基础设施500米口径球面射电望远镜（ＦＡＳＴ）项目奠基</span> |language=zh |publisher=Guizhou Daily |date=27 December 2008 |access-date=28 December 2008 |url-status=dead |archive-url=https://web.archive.org/web/20090112030246/http://gzrb.gog.com.cn/system/2008/12/27/010441147.shtml |archive-date=12 January 2009}}</ref> Construction started in March 2011,{{r|gm}}<ref name=arxiv>{{cite journal |arxiv=1105.3794 |title=The Five-Hundred-Meter Aperture Spherical Radio Telescope (FAST) Project |author1=Rendong Nan |author2=Di Li |author3=Chengjin Jin |author4=Qiming Wang |author5=Lichun Zhu |author6=Wenbai Zhu |author7=Haiyan Zhang |author8=Youling Yue |author9=Lei Qian |journal=International Journal of Modern Physics D |volume=20 |issue=6 |pages=989–1024 |date=20 May 2011 |doi=10.1142/S0218271811019335 |bibcode=2011IJMPD..20..989N |s2cid=26433223}}</ref> and the last panel was installed on the morning of 3 July 2016.{{r|Xinhua complete|arxiv}}<ref>{{cite news |title=China completes installation of world's largest telescope |date=3 July 2016 |journal=The BRICS Post |url=http://thebricspost.com/china-completes-installation-of-worlds-largest-telescope/ |access-date=3 July 2016 |archive-date=19 April 2019 |archive-url=https://web.archive.org/web/20190419162257/http://www.thebricspost.com/china-completes-installation-of-worlds-largest-telescope/ |url-status=live }}</ref><ref name="CNN 2015">{{cite news |last=McKirdy |first=Euan |url=http://www.cnn.com/2015/10/11/tech/china-fast-telescope/index.html |title=China looks to the stars with creation of world's largest radio telescope |work=CNN News |date=12 October 2015 |access-date=19 October 2015 |archive-date=19 October 2015 |archive-url=https://web.archive.org/web/20151019000707/http://www.cnn.com/2015/10/11/tech/china-fast-telescope/index.html |url-status=live }}</ref>

Originally budgeted for {{CNY|700 million|link=yes}},{{r|Nan 2009|p=49|}}<ref name="gm">{{cite web |url=http://www.gizmag.com/five-hundred-meter-aperture-spherical-radio-telescope/18930/ |title=China building world's biggest radio telescope |first=Darren |last=Quick |date=16 June 2011 |access-date=13 August 2012 |work=gizmag |archive-date=19 November 2012 |archive-url=https://web.archive.org/web/20121119193012/http://www.gizmag.com/five-hundred-meter-aperture-spherical-radio-telescope/18930/ |url-status=live }}</ref> the final cost was {{CNY|1.2 billion}} ({{US$|180 million}}).{{r|Xinhua complete}}<ref name=wanted>{{cite news |title=Wanted: Researchers for China's mega telescope to interpret signals from across the universe |date=31 October 2018 |first=Alice |last=Shen |journal=South China Morning Post |url=https://www.scmp.com/news/china/science/article/2171002/wanted-researchers-chinas-mega-telescope-interpret-signals-across |access-date=8 November 2018 |archive-date=9 January 2020 |archive-url=https://web.archive.org/web/20200109183659/https://www.scmp.com/news/china/science/article/2171002/wanted-researchers-chinas-mega-telescope-interpret-signals-across |url-status=live }}</ref> Significant difficulties encountered were the site's remote location and poor road access, and the need to add shielding to suppress radio-frequency interference (RFI) from the primary mirror actuators.{{r|Normile}} The actuators were redesigned to meet shielding efficiency requirements and their installation was completed in 2015. Interference from the actuators has not been detected since.<ref>{{Cite journal |last1=Zhang |first1=Hai-Yan |last2=Wu |first2=Ming-Chang |last3=Yue |first3=You-Ling |last4=Gan |first4=Heng-Qian |last5=Hu |first5=Hao |last6=Huang |first6=Shi-Jie |date=2018-04-01 |title=EMC design for actuators in the FAST reflector |url=https://iopscience.iop.org/article/10.1088/1674-4527/18/4/48/meta |journal=Research in Astronomy and Astrophysics |language=en |volume=18 |issue=4 |page=048 |doi=10.1088/1674-4527/18/4/48 |arxiv=1802.02315 |bibcode=2018RAA....18...48Z |s2cid=116359320 |issn=1674-4527 |access-date=12 June 2022 |archive-date=15 June 2022 |archive-url=https://web.archive.org/web/20220615184324/https://iopscience.iop.org/article/10.1088/1674-4527/18/4/48/meta |url-status=live }}</ref>

Testing and commissioning began with first light on 25 September 2016.<ref name="Morelle BBC">{{cite news |last=Morelle |first=Rebecca |url=https://www.bbc.com/news/science-environment-37453933 |title=China's colossal radio telescope begins testing |work=BBC News |date=25 September 2016 |access-date=25 September 2016 |archive-date=25 September 2016 |archive-url=https://web.archive.org/web/20160925140311/http://www.bbc.com/news/science-environment-37453933 |url-status=live }}</ref> The first observations are being done without the active primary reflector, configuring it in a fixed shape and using the Earth's rotation to scan the sky.{{r|Normile}} Subsequent early science took place mainly in lower frequencies<ref>{{Cite conference |title=FAST low frequency pulsar survey |first1=Youling |last1=Yue |first2=Di |last2=Li |first3=Rendong |last3=Nan |arxiv=1211.0748 |conference=Neutron Stars and Pulsars: Challenges and Opportunities after 80 years |conference-url=http://www.pulsarastronomy.net/IAUS291/ |date=20–31 August 2012 |doi=10.1017/S174392131300001X |access-date=26 September 2016 |archive-date=30 May 2017 |url=http://www.pulsarastronomy.net/IAUS291/ |archive-url=https://web.archive.org/web/20170530173653/http://www.pulsarastronomy.net/IAUS291/ |url-status=live }}</ref> while the active surface is brought to its design accuracy;<ref>{{cite conference |title=The Five-hundred-meter Aperture Spherical Radio Telescope Project and its Early Science Opportunities |first1=Di |last1=Li |first2=Rendong |last2=Nan |first3=Zhichen |last3=Pan |arxiv=1210.5785 |conference=Neutron Stars and Pulsars: Challenges and Opportunities after 80 years |conference-url=http://www.pulsarastronomy.net/IAUS291/ |date=20–31 August 2012 |doi=10.1017/S1743921312024015 |access-date=26 September 2016 |archive-date=30 May 2017 |url=http://www.pulsarastronomy.net/IAUS291/ |archive-url=https://web.archive.org/web/20170530173653/http://www.pulsarastronomy.net/IAUS291/ |url-status=live }} Video available at http://www.pulsarastronomy.net/IAUS291/video/DiLi/ {{Webarchive|url=https://web.archive.org/web/20180824173206/http://www.pulsarastronomy.net/IAUS291/video/DiLi/ |date=24 August 2018 }}</ref> longer wavelengths are less sensitive to errors in reflector shape. It took three years to calibrate the various instruments so it can become fully operational.{{r|Morelle BBC}}

Local government efforts to develop a tourist industry around the telescope are causing some concern among astronomers worried about nearby mobile telephones acting as sources of RFI.<ref>{{cite news |url=http://english.caixin.com/2016-09-26/100992047.html |title=Scientists Concerned About Plans to Make Telescope a Tourist Attraction |first1=Zhou |last1=Chen |first2=Wu |last2=Gang |journal=Caixin Online |access-date=26 September 2016 |archive-date=18 November 2016 |archive-url=https://web.archive.org/web/20161118064534/http://english.caixin.com/2016-09-26/100992047.html |url-status=live }}</ref> A projected 10 million tourists in 2017 will force officials to decide on the scientific mission versus the economic benefits of tourism.<ref>{{cite news |last1=Chen |first1=Stephen |title=How noisy Chinese tourists may be drowning out alien signals at the world's biggest telescope |url=http://www.scmp.com/news/china/society/article/2107893/how-noisy-chinese-tourists-may-be-drowning-out-alien-signals |access-date=24 August 2017 |work=South China Morning Post |date=24 August 2017 |archive-date=24 August 2017 |archive-url=https://web.archive.org/web/20170824000945/http://www.scmp.com/news/china/society/article/2107893/how-noisy-chinese-tourists-may-be-drowning-out-alien-signals |url-status=live }}</ref>{{needs update|date=December 2023}}

The primary driving force behind the project{{r|Normile}} was [[Biography:Nan Rendong|Nan Rendong]], a researcher with the Chinese National Astronomical Observatory, part of the Chinese Academy of Sciences. He held the positions of chief scientist{{r|CNN 2015}} and chief engineer{{r|Normile}} of the project. He died on 15 September 2017 in Boston due to lung cancer.<ref>{{cite news |url=http://www.chinanews.com/m/gn/2017/09-16/8332735.shtml |title=<span lang="zh-Hans">中国天眼"首席科学家南仁东病逝 享年72岁</span> |journal=China News Service |date=16 September 2017 |language=zh-Hans |access-date=17 September 2017 |archive-date=29 June 2019 |archive-url=https://web.archive.org/web/20190629122042/http://www.chinanews.com/m/gn/2017/09-16/8332735.shtml |url-status=live }}</ref>

On 14 June 2022, astronomers, working with China's FAST telescope, reported the possibility of having detected artificial (presumably alien) signals, but cautioned that further studies are required to determine if some kind of natural radio interference may be the source.<ref name="ES-20220614">{{cite news |last=Byrd |first=Deborah |title=Has China's FAST telescope detected alien intelligence? |url=https://earthsky.org/space/did-chinas-fast-telescope-detect-alien-intelligence/ |date=4 June 2022 |work=Earth & Sky |accessdate=15 June 2022 |archive-date=15 June 2022 |archive-url=https://web.archive.org/web/20220615154041/https://earthsky.org/space/did-chinas-fast-telescope-detect-alien-intelligence/ |url-status=live }}</ref><ref>{{cite news|title=Alien hunters detect mystery radio signal from direction of Earthlike planet|author=Ling Xin|newspaper=South China Morning Post|date=June 15, 2022|url=https://www.scmp.com/news/china/science/article/3181832/alien-hunters-detect-mystery-radio-signal-direction-earthlike|quote=Narrowband signal picked up from direction of the Kepler-438 star meets initial criteria for extraterrestrial intelligence, preprint says; orbiting Kepler-438 in its habitable zone is one of the most Earthlike planets ever found outside the solar system.}}</ref> More recently, on 18 June 2022, Dan Werthimer, chief scientist for several SETI-related projects, noted, "These signals are from radio interference; they are due to radio pollution from earthlings, not from E.T."<ref name="NYT-20220618">{{cite news |last=Overbye |first=Dennis |title=A Chinese Telescope Did Not Find an Alien Signal. The Search Continues. China's astronomers have been initiated into the search for extraterrestrial intelligence with the kind of false alarm that others in the field have experienced for decades. |url=https://www.nytimes.com/2022/06/18/science/china-alien-signal.html |date=18 June 2022 |work={{wipe|The New York Times}} |accessdate=19 June 2022 }}</ref>

==Overview==
FAST has a reflecting surface {{convert|500|m|ft}} in diameter located in a natural [[Earth:Sinkhole|sinkhole]] in the [[Earth:Karst|karst rock landscape]], focusing radio waves on a receiving antenna in a "feed cabin" suspended {{cvt|140|m}} above it. The reflector is made of perforated aluminium panels supported by a mesh of steel cables hanging from the rim.

FAST's surface is made of 4,450{{r|Xinhua complete}} triangular panels, {{cvt|11|m}} on a side,<ref>{{Cite news |title=China assembles world's largest telescope in Guizhou |date=24 July 2015 |url=http://www.china.org.cn/china/2015-07/24/content_36136455.htm |publisher=Xinhua |via=China.org.cn |access-date=6 July 2016 |archive-date=23 August 2018 |archive-url=https://web.archive.org/web/20180823141820/http://www.china.org.cn/china/2015-07/24/content_36136455.htm |url-status=live }}</ref> in the form of a geodesic dome. There are 2,225 winches located underneath<ref name=Normile>{{cite news |title=World's largest radio telescope will search for dark matter, listen for aliens |first=Dennis |last=Normile |date=26 September 2016 |journal=Science News |url=http://www.sciencepubs.com/news/2016/09/world-s-largest-radio-telescope-will-search-dark-matter-listen-aliens |doi=10.1126/science.aah7346 |access-date=28 September 2016 |archive-date=1 October 2016 |archive-url=https://web.archive.org/web/20161001193952/http://www.sciencepubs.com/news/2016/09/world-s-largest-radio-telescope-will-search-dark-matter-listen-aliens |url-status=live }}</ref> make it an [[Astronomy:Active optics|active surface]], pulling on joints between panels, deforming the flexible steel cable support into a [[Astronomy:Parabolic antenna|parabolic antenna]] aligned with the desired sky direction.<ref name=ohio>{{Cite report |first=R.L. II |last=Williams |title=Five-Hundred Meter Aperture Spherical Radio Telescope (FAST) Cable-Suspended Robot Model and Comparison with the Arecibo Observatory |url=http://www.ohio.edu/people/williar4/html/pdf/FAST.pdf |institution=Ohio University |date=July 2015 |access-date=6 July 2016 |archive-url=https://web.archive.org/web/20161022030530/http://www.ohio.edu/people/williar4/html/pdf/FAST.pdf |archive-date=22 October 2016 |url-status=dead}} Although this source contains wealth of detail, its reliability is questionable. It describes in some detail (at the end of p. 4) the fact that FAST's dish is actually 519.6&nbsp;m in diameter; papers published by the project scientists, who would presumably know, are explicit that the dish extends "up to a girder ring of exactly 500&nbsp;m diameter".</ref>

[[File:Bottom view from one of FAST's six support towers.jpg|One of six support towers for the feed cabin|thumb|left]]

Above the reflector is a lightweight feed cabin moved by a [[Engineering:Cable robots|cable robot]] using winch [[Servomechanism|servomechanism]]s on six support towers.{{r|arxiv|p=13}} The receiving antennas are mounted below this on a [[Stewart platform]] which provides fine position control and compensates for disturbances like wind motion.{{r|arxiv|p=13}} This produces a planned pointing precision of 8 arcseconds.<ref name=Nan11/>

[[File:Fast Illuminated aperture.png|thumb|upright=1.25|300&nbsp;m illuminated aperture within 500&nbsp;m dish|right]]

The maximum [[Zenith|zenith angle]] is 40 degrees when the effective illuminated aperture is reduced to 200 m, while it is 26.4 degrees when the effective illuminated aperture is 300 m without loss.<ref name=ISAP2013>{{cite journal |title=The optics of the Five-hundred-meter Aperture Spherical radio Telescope |author=Jin Chengjin |display-authors=0 |journal=International Symposium on Antennas and Propagation |date=23 October 2013 |url=http://ap-s.ei.tuat.ac.jp/isapx/2013/pdf/339_2_0.pdf |access-date=9 July 2016 |archive-date=16 August 2016 |archive-url=https://web.archive.org/web/20160816125644/http://ap-s.ei.tuat.ac.jp/isapx/2013/pdf/339_2_0.pdf |url-status=live }}</ref>{{r|Nan 2009|p=13}}

Although the reflector diameter is {{cvt|500|m}}, held in the correct parabolic shape and "illuminated" by the receiver, only a circle of 300&nbsp;m diameter is useful at any one time.{{r|arxiv|p=13}} The telescope can be pointed to different positions on the sky by illuminating a 300-meter section of the 500 meter aperture. (FAST has a smaller effective aperture than the [[Astronomy:Jicamarca Radio Observatory|Jicamarca Radio Observatory]], which has a filled aperture of equivalent diameter of 338 m).<!-- Pretty sure this is a historical accident: it was planned to be more Arecibo-like, but the larger size made the heavy aberration-compensating receiver impractical to suspend. --><!-- Actually, probably not; it appears to be derived from the earlier KARST proposal for the SKA, which already had the deformable primary. And Arecibo doesn't have a full-aperture primary, either!-->

Its working frequency ranges from 70&nbsp;MHz to 3.0&nbsp;GHz,<ref>{{cite web |title=Receiver Systems |url=http://fast.bao.ac.cn/en/Receiver.html |website=FAST Home Page |publisher=National Astronomical Observatories, Chinese Academy of Sciences |access-date=28 June 2014 |archive-date=17 October 2017 |archive-url=https://web.archive.org/web/20171017203640/http://fast.bao.ac.cn/en/Receiver.html |url-status=dead }}</ref> with the upper limit set by the precision with which the primary can approximate a parabola. It could be improved slightly, but the size of the triangular segments limits the shortest wavelength which can be received. The original plan was to cover the frequency range with 9 receivers. During the construction phase, a commissioning ultra-wide band receiver covering 260&nbsp;MHz to 1620&nbsp;MHz was proposed and built, which produced the first pulsar discovery from FAST.<ref name=Qian19>{{cite journal |title=The first pulsar discovered by FAST |first=Lei |last=Qian |institution=CAS Key Laboratory of FAST, National Astronomical Observatories, Chinese Academy of Sciences |journal=Science China Physics, Mechanics & Astronomy |volume=62 |issue=5 |id=959508 |pages=4 pp |date=May 2019 |doi=10.1007/s11433-018-9354-y |url=https://doi.org/10.1007/s11433-018-9354-y |arxiv=1903.06318 |bibcode=2019SCPMA..6259508Q |s2cid=119479606 |access-date=25 January 2021 |archive-date=15 June 2022 |archive-url=https://web.archive.org/web/20220615184408/https://link.springer.com/article/10.1007/s11433-018-9354-y |url-status=live }}</ref> At the moment, only the FAST L-band Receiver-array of 19 beams (FLAN<ref name=Li18/>) is installed and is operational between 1.05&nbsp;GHz and 1.45&nbsp;GHz.

The Next Generation Archive System (NGAS), developed by the [[Organization:International Centre for Radio Astronomy Research|International Centre for Radio Astronomy Research]] (ICRAR) in Perth, Australia and the [[Organization:European Southern Observatory|European Southern Observatory]] will store and maintain the large amount of data that it collects.<ref>{{Cite news |url=http://www.skyandtelescope.com/astronomy-blogs/astronomy-space-david-dickinson/fast-worlds-largest-radio-telescope-open/ |title=FAST Radio Telescope Open for Business |date=27 September 2016 |newspaper=Sky & Telescope |language=en-US |access-date=2016-10-10 |archive-date=10 October 2016 |archive-url=https://web.archive.org/web/20161010211519/http://www.skyandtelescope.com/astronomy-blogs/astronomy-space-david-dickinson/fast-worlds-largest-radio-telescope-open/ |url-status=live }}</ref>

A five-kilometre zone near the telescope forbids tourists from using mobile phones and other radio-emitting devices.<ref>{{Cite news |title=China Finds Phone-Wielding Tourists and Telescopes Don't Mesh |language=en-US |magazine=Wired |url=https://www.wired.com/story/china-finds-phone-wielding-tourists-and-telescopes-dont-mesh/ |access-date=2021-04-26 |issn=1059-1028 |archive-date=26 April 2021 |archive-url=https://web.archive.org/web/20210426202731/https://www.wired.com/story/china-finds-phone-wielding-tourists-and-telescopes-dont-mesh/ |url-status=live }}</ref>

==Science mission==
The FAST website lists the following science objectives of the radio telescope:<ref>{{Cite web |url=http://fast.bao.ac.cn/en/Science.html |title=Science |access-date=19 February 2017 |archive-date=18 November 2019 |archive-url=https://web.archive.org/web/20191118041114/http://fast.bao.ac.cn/en/Science.html |url-status=live }}</ref>

# Large scale neutral hydrogen survey
# [[Astronomy:Pulsar|Pulsar]] observations
# Leading the international very long baseline interferometry (VLBI) network
# Detection of [[Physics:List of interstellar and circumstellar molecules|interstellar molecules]]
# Detecting interstellar communication signals ([[Astronomy:Search for extraterrestrial intelligence|Search for extraterrestrial intelligence]])
# [[Astronomy:Pulsar timing array|Pulsar timing array]]s<ref>{{cite arXiv |title=The Role of FAST in Pulsar Timing Arrays |first1=G. |last1=Hobbs |first2=S. |last2=Dai |first3=R.N. |last3=Manchester |first4=R.M. |last4=Shannon |first5=M. |last5=Kerr |first6=K.J. |last6=Lee |first7=R. |last7=Xu |date=1 July 2014 |eprint=1407.0435 |class=astro-ph.IM}}</ref>

The FAST telescope joined the [[Astronomy:Breakthrough Listen|Breakthrough Listen]] SETI project in October 2016 to search for intelligent extraterrestrial communications in the Universe.<ref>{{cite press release |url=http://astrobiology.com/2016/10/national-astronomical-observatories-of-china-breakthrough-initiatives-launch-global-collaboration-in.html |title=National Astronomical Observatories of China, Breakthrough Initiatives Launch Global Collaboration in Search for Intelligent life in the Universe |publisher=Breakthrough Initiatives |via=Astrobiology Web |date=12 October 2016 |access-date=24 August 2017 |archive-date=15 June 2022 |archive-url=https://web.archive.org/web/20220615184323/http://astrobiology.com/2016/10/national-astronomical-observatories-of-china-breakthrough-initiatives-launch-global-collaboration-in.html |url-status=live }}</ref>

In February 2020, scientists announced the first SETI observations with the telescope.<ref>{{Cite journal |last1=Zhang |first1=Zhi-Song |last2=Werthimer |first2=Dan |last3=Zhang |first3=Tong-Jie |last4=Cobb |first4=Jeff |last5=Korpela |first5=Eric |last6=Anderson |first6=David |last7=Gajjar |first7=Vishal |last8=Lee |first8=Ryan |last9=Li |first9=Shi-Yu |last10=Pei |first10=Xin |last11=Zhang |first11=Xin-Xin |date=2020-03-17 |title=First SETI Observations with China's Five-hundred-meter Aperture Spherical radio Telescope (FAST) |journal=The Astrophysical Journal |volume=891 |issue=2 |pages=174 |doi=10.3847/1538-4357/ab7376 |issn=1538-4357 |arxiv=2002.02130 |bibcode=2020ApJ...891..174Z |s2cid=211043944 |doi-access=free }}</ref>

China's ''Global Times'' reported that its 500-meter (1,600 foot) FAST telescope will be open to the global scientific community starting in April 2021 (when applications will be reviewed), and becoming effective in August 2021. Foreign scientists will be able to submit applications to China's National Astronomical Observatories online.<ref>{{cite news |last=Dent |first=Steve |title=China's huge FAST telescope will open to scientists globally in April |language=en |publisher=Engadget (via Yahoo! Finance) |date=4 January 2021 |url=https://finance.yahoo.com/news/china-will-open-its-500-meter-satellite-to-astronomers-across-the-world-105359520.html |access-date=5 January 2021 |archive-date=4 January 2021 |archive-url=https://web.archive.org/web/20210104151515/http://finance.yahoo.com/news/china-will-open-its-500-meter-satellite-to-astronomers-across-the-world-105359520.html |url-status=live }}</ref><ref>{{cite web |title=China's FAST telescope will be available to foreign scientists - Xinhua {{!}} English.news.cn |url=http://www.xinhuanet.com/english/2021-01/04/c_139640756.htm |website=www.xinhuanet.com |access-date=4 January 2021 |archive-date=4 January 2021 |archive-url=https://web.archive.org/web/20210104212427/http://www.xinhuanet.com/english/2021-01/04/c_139640756.htm |url-status=live }}</ref>

==Comparison with Arecibo Telescope==

The basic design of FAST is similar to the former [[Astronomy:Arecibo Telescope|Arecibo Telescope]]. Both designs had reflectors installed in natural hollows within karst limestone, made of perforated aluminium panels with a movable receiver suspended above; and both have an effective aperture smaller than the physical size of the primary. There are however significant differences in addition to the size.{{r|ohio}}<ref name=optics>{{cite conference |title=The optics of the Five-hundred-meter Aperture Spherical radio Telescope |conference=International Symposium on Antennas and Propagation |location=Nanjing |date=23 October 2013 |first1=Chengjin |last1=Jin |first2=Kai |last2=Zhu |first3=Jin |last3=Fan |first4=Hongfei |last4=Liu |first5=Yan |last5=Zhu |first6=Hengqian |last6=Gan |first7=Jinglong |last7=Yu |first8=Zhisheng |last8=Gao |first9=Yang |last9=Cao |first10=Yang |last10=Wu |institution=National Astronomical Observatories, Chinese Academy of Sciences |url=http://ap-s.ei.tuat.ac.jp/isapx/2013/pdf/339_2_0.pdf |conference-url=http://ap-s.ei.tuat.ac.jp/isapx/2013/ |access-date=9 July 2016 |archive-date=16 August 2016 |archive-url=https://web.archive.org/web/20160816125644/http://ap-s.ei.tuat.ac.jp/isapx/2013/pdf/339_2_0.pdf |url-status=live }}</ref><ref name=Qiu11>{{cite journal |title=A novel design for a giant Arecibo-type spherical radio telescope with an active main reflector |first=Yuhai H. |last=Qiu |institution=Beijing Astronomical Observatory, The Chinese Academy of Sciences |journal=[[Organization:Monthly Notices of the Royal Astronomical Society|Monthly Notices of the Royal Astronomical Society]] |volume=301 |issue=3 |pages=827–830 |date=11 December 1998 |doi=10.1111/j.1365-8711.1998.02067.x |bibcode=1998MNRAS.301..827Q |doi-access=free}}</ref>

First, Arecibo's dish was fixed in a spherical shape. Although it was also suspended from steel cables with supports underneath for fine-tuning the shape, they were manually operated and adjusted only during maintenance.{{r|ohio}} It had a fixed spherical shape with two additional suspended reflectors in a [[Astronomy:Gregorian telescope|Gregorian]] configuration to correct for [[Physics:Spherical aberration|spherical aberration]].<ref>{{cite report |title=AOPAF: Arecibo Observatory Phased Array Feed |first=Germán |last=Cortés-Medellín |date=13 September 2010 |institution=National Astronomy and Ionosphere Center, [[Organization:Cornell University|Cornell University]] |url=https://www.naic.edu/~phil/hardware/byuPhasedAr/logs/Cortes%20AOPAF_short%20report%20Sept%202010-1.pdf |access-date=27 September 2016 |url-status=live |archive-url=https://web.archive.org/web/20180508145854/http://www.naic.edu/~phil/hardware/byuPhasedAr/logs/Cortes%20AOPAF_short%20report%20Sept%202010-1.pdf |archive-date=8 May 2018}}</ref>

Second, Arecibo's receiver platform was fixed in place. To support the greater weight of the additional reflectors, the primary support cables were static, with the only motorised portion being three hold-down winches which compensated for [[Physics:Thermal expansion|thermal expansion]].{{r|ohio|p=3}} The antennas could move along a rotating arm below the platform, to allow limited adjustment of azimuth,{{r|ohio|p=4}} although Arecibo was not limited in azimuth, only in zenith angle: The smaller range of motion limited it to viewing objects within 19.7° of the zenith.<ref name=Arecibo>{{cite web |title=Arecibo: General statistical information on the antenna |date=3 January 2005 |website=National Astronomy and Ionosphere Center |url=https://www.naic.edu/~astro/general_info/basic.shtml |url-status=live |access-date=5 July 2016 |archive-url=https://web.archive.org/web/20160818145045/http://www.naic.edu/~astro/general_info/basic.shtml |archive-date=18 August 2016}}</ref>

Third, Arecibo could receive higher frequencies. The finite size of the triangular panels making up FAST's primary reflector limits the accuracy with which it can approximate a parabola, and thus the shortest wavelength it can focus. Arecibo's more rigid design allowed it to maintain sharp focus down to 3&nbsp;cm wavelength (10&nbsp;GHz); FAST is limited to 10&nbsp;cm (3&nbsp;GHz). Improvements in position control of the secondary might be able to push that to 6&nbsp;cm (5&nbsp;GHz), but then the primary reflector becomes a hard limit.

Fourth, the FAST dish is significantly deeper, contributing to a wider field of view. Although {{#expr:100*(500 / {{cvt|1000|ft|m|5|disp=number}} - 1) round 0}}% larger in diameter, FAST's radius of curvature is {{cvt|300|m}},{{r|arxiv|p=3}} barely larger than Arecibo's {{cvt|870|ft|order=flip}},{{r|Arecibo}} so it forms a {{#expr:360/pi*asin(500/2/300) round 0}}° arc{{r|arxiv|p=4}} (vs. {{#expr:360/pi*asin(1000/2/870) round 0}}° for Arecibo). Although Arecibo's full aperture of {{cvt|1000|ft|m|0|order=flip}} could be used when observing objects at the [[Zenith|zenith]], this was only possible with the line feed which had a very narrow frequency range and had been unavailable due to damage since 2017.<ref name=":0">{{cite web |title=The Arecibo observatory and its telescope |url=https://www.naic.edu/~astro/guide/node2.html |access-date=1 December 2020 |url-status=live |archive-url=https://web.archive.org/web/20190910163813/http://www2.naic.edu/~astro/guide/node2.html |archive-date=10 September 2019}}</ref> Most Arecibo observations used the Gregorian feeds, where the effective aperture was approximately {{cvt|725|ft|m|order=flip}} at zenith.<ref name=":0"/>{{r|ohio|p=4}}

Fifth, Arecibo's larger secondary platform also housed several ''transmitters'', making it one of the few instruments in the world capable of [[Astronomy:Radar astronomy|radar astronomy]]. (Planetary radar is also possible at the Jicamarca and Millstone and Altair observatories.) The NASA-funded Planetary Radar System allowed Arecibo to study solid objects from Mercury to Saturn, and to perform very accurate [[Astronomy:Orbit determination|orbit determination]] on near-earth objects, particularly [[Astronomy:Potentially hazardous object|potentially hazardous object]]s. Arecibo also included several NSF funded radars for ionospheric studies ([[Ionosonde|ionosonde]]s). Such powerful transmitters are too large and heavy for FAST's small receiver cabin, so it will not be able to participate in planetary defense although in principle it could serve as a receiver in a [[Physics:Bistatic radar|bistatic radar]] system. (Arecibo has been used in several multi-static experiments with an auxiliary 100&nbsp;meter dish, including S-band radar experiments in the stratosphere, and ISAR mapping of Venus.)

==See also==
* Chinese space program
* [[Astronomy:KARST|KARST]] – a 1990s Chinese proposal to host the SKA
* [[Astronomy:List of telescope types|List of telescope types]]
* [[Astronomy:Square Kilometre Array|Square Kilometre Array]] – a proposed 1&nbsp;km<sup>2</sup> telescope array in Australia and South Africa

==References==
{{Reflist}}

==Further reading==
* {{cite web |title=Kilometer-square Area Radio Synthesis Telescope – KARST |first=R. |last=Nan|display-authors=0 |url=http://www.skatelescope.org/documents/SKA_CHN_CONCEPT_Karst_17062002.pdf |date=16 June 2002 |url-status=dead |archive-url=https://web.archive.org/web/20061029202520/http://www.skatelescope.org/documents/SKA_CHN_CONCEPT_Karst_17062002.pdf |archive-date=29 October 2006 |df=dmy-all}}
* {{cite journal |title=The FAST telescope and its possible contribution to high precision astrometry |first1=C. J. |last1=Jin |first2=R. D. |last2=Nan |first3=H. Q. |last3=Gan |journal=Proceedings of the International Astronomical Union |volume=3 |issue=S248 |pages=178–181 |date=October 2007 |url=https://www.cambridge.org/core/services/aop-cambridge-core/content/view/1F91AA86ABBD28527A4887B59562C38C/S1743921308018978a.pdf/fast_telescope_and_its_possible_contribution_to_high_precision_astrometry.pdf |doi=10.1017/S1743921308018978|doi-access=free |bibcode=2008IAUS..248..178J}}
* {{cite journal |title=The Five-hundred-meter Aperture Spherical Radio Telescope (FAST) Project |arxiv=1612.09372 |first1=Di |last1=Li |first2=Zhichen |last2=Pan |date=30 December 2016 |doi=10.1002/2015RS005877 |volume=51 |issue=7 |journal=Radio Science |pages=1060–1064 |bibcode=2016RaSc...51.1060L |s2cid=119363387}}

==External links==
* [https://fast.bao.ac.cn/ Five-hundred-meter Aperture Spherical radio Telescope – website]
* {{YouTube|7SRV3rnULO0|FAST: The World's Largest Telescope – China Icons}} (25 September 2016)
* [http://zmtt.bao.ac.cn/GPPS/ The FAST Galactic Plane Pulsar Snapshot survey]

{{Radio astronomy}}

{{DEFAULTSORT:Five Hundred Meter Aperture Spherical Telescope}}
[[Category:Chinese telescopes]]
[[Category:Radio telescopes]]
[[Category:Search for extraterrestrial intelligence]]

{{Sourceattribution|Five-hundred-meter Aperture Spherical Telescope}}