{{Short description|Persian astronomer (1201–1274)}}{{Similar names|Al-Tusi}}{{Infobox religious biography
| religion         = [[Islam]]
<!-- Please note the background of Tusi is constantly vandalized by ips- that is why it is sourced more predominantly here-->
| era              = [[Islamic Golden Age]]
| image            = Nasir al-Din Tusi.jpg
| image_size       = 
| caption          = Iranian stamp for the 700th anniversary of his death
| name             = Naṣīr al-Dīn al-Ṭūsī
| title            = Khawaja Nasir
| birth_date       = 18 February 1201 <br />[[Tus, Iran|Tus]], [[Greater Khorasan|Khurasan]], [[Khwarazmian dynasty|Khwarazmid Empire]]
| death_date       = {{Death date and age|df=yes|1274|06|26|1201|02|18}} <br />[[Al-Kadhimiya Mosque]], [[Kadhimiya]], [[Baghdad]], [[Ilkhanate]]
| region           = [[Persia]] ([[Iran]])
| denomination     = [[Shia]]
| sect            = [[Ismai'ili]] (Initially)<br/>[[Twelver]]<ref>{{cite encyclopedia|first=John|last=Cooper|author-link=John Cooper (Islamic studies scholar)|year=1998|title=al-Tusi, Khwajah Nasir (1201–74)|encyclopedia=[[Routledge Encyclopedia of Philosophy|Encyclopedia of Philosophy]]|publisher=[[Routledge]]|url=https://www.muslimphilosophy.com/ip/rep/H036.htm}}</ref>
| jurisprudence    = [[Ja'fari]]
| main_interests   = [[Kalam]], [[Early Islamic philosophy|Islamic Philosophy]], [[Islamic astronomy|Astronomy]], [[Islamic mathematics|Mathematics]], [[Islamic medicine|Biology and Medicine]], [[Islamic physics|Physics]], [[Islamic science|Science]]
| notable_ideas    = [[Spherical trigonometry]], [[Tusi couple]]
| notable_works    = ''[[Tajrid al-I'tiqad]]'', ''[[Zij-i ilkhani]]'', ''Rawḍa-yi Taslīm'', ''[[Akhlaq-i Nasiri]]'', ''al-Risalah al-Asturlabiyah'', ''Al-Tadhkirah fi 'Ilm al-Hay'ah'' (Memoir on the Science of Astronomy)
| teacher          = [[Kamal al-Din ibn Yunus]]<ref name=MacT/>
| students         = [[Shams al-Din al-Bukhari]]<ref name="Shams">{{MathGenealogy|id=204293|name=Shams al‐Dīn al‐Bukhārī}}</ref>
| influences       = [[Avicenna]], [[Fakhr al-Din Razi]], [[Mo'ayyeduddin Urdi]], [[Siraj Qumri]]
| influenced       = [[Maitham Al Bahrani]], [[ibn Khaldun]], [[Qutb al-Din Shirazi]], [[Ibn al-Shatir]], [[Copernicus]]
| native_name      = {{nobold|نصیرالدین طوسی}}
| native_name_lang = fa
}}

'''Muḥammad ibn Muḥammad ibn al-Ḥasan al-Ṭūsī''' (1201–1274),{{Efn|{{langx|fa|ابوجعفر محمد خواجه نصیرالدین طوسی}}{{hairsp}}<ref>{{Cite encyclopedia| encyclopedia=Encyclopædia Iranica |url=http://www.iranicaonline.org/articles/tusi-nasir-al-din-bio |title=ṬUSI, NAṢIR-AL-DIN i. Biography |access-date=2018-08-05}}</ref>}} also known as '''Naṣīr al-Dīn al-Ṭūsī'''<ref>{{cite book |last1=Lameer |first1=Joep |title=The Arabic Version of Ṭūsī's Nasirean Ethics |date=2015 |publisher=Brill |isbn=978-9004304505 |url=https://brill.com/display/title/32371}}</ref> ({{langx|ar|نصیر الدین الطوسی}}; {{langx|fa|نصیر الدین طوسی}}) or simply as '''(al-)Tusi''', was a [[Persians|Persian]] [[polymath]], architect, [[Early Islamic philosophy|philosopher]], [[Islamic medicine|physician]], [[Islamic science|scientist]], and [[kalam|theologian]].<ref>Multiple sources:
* {{cite book|last1=Bennison|first1=Amira K.|title=The great caliphs : the golden age of the 'Abbasid Empire |date=2009 |publisher=Yale University Press |location=New Haven |isbn=978-0-300-15227-2 |page=204 |quote=Hulegu killed the last ‘Abbasid caliph but also patronized the foundation of a new observatory at Maragha in Azerbayjan at the instigation of the Persian Shi‘i polymath Nasir al-Din Tusi.}}
* {{cite book|last1=Goldschmidt|first1=Arthur |last2=Boum|first2=Aomar |title=A Concise History of the Middle East|url=https://books.google.com/books?id=hSOdBAAAQBAJ |year=2015 |publisher=Avalon Publishing |isbn=978-0-8133-4963-3 |quote=Hulegu, contrite at the damage he had wrought, patronized the great Persian scholar, Nasiruddin Tusi (died 1274), who saved the lives of many other scientists and artists, accumulated a library of 400000 volumes, and built an astronomical ...}}
* {{cite book|author1=Bar Hebraeus |author-link1=Bar Hebraeus|last2=Joosse|first2=Nanne Pieter George|title=A Syriac Encyclopaedia of Aristotelian Philosophy: Barhebraeus (13th C.), Butyrum Sapientiae, Books of Ethics, Economy, and Politics : a Critical Edition, with Introduction, Translation, Commentary, and Glossaries|url=https://books.google.com/books?id=eYV3AAAAMAAJ|year=2004 |publisher=Brill |isbn=978-90-04-14133-9|page=11|quote=the Persian scholar Naṣīr al-Dīn al-Ṭūsī}}
* {{cite book |author=Seyyed Hossein Nasr|title=Islamic Philosophy from Its Origin to the Present: Philosophy in the Land of Prophecy |url=https://books.google.com/books?id=0k5iy4RvAwcC |year=2006 |publisher=State University of New York Press |isbn=978-0-7914-6800-5 |page=167 |quote=In fact it was common among Persian Islamic philosophers to write few quatrains on the side often in the spirit of some of the poems of Khayyam singing about the impermanence of the world and its transience and similar themes. One needs to only recall the names of Ibn Sina, Suhrawardi, Nasir al-Din Tusi and Mulla Sadra, who wrote poems along with extensive prose works.}}
* Rodney Collomb, "The rise and fall of the Arab Empire and the founding of Western pre-eminence", Published by Spellmount, 2006. pg 127: "Khawaja Nasr ed-Din Tusi, the Persian, Khorasani, former chief scholar and scientist of"
* Seyyed Hossein Nasr, [[Islamic Philosophy from its Origin to the Present: Philosophy in the Land of Prophecy|Islamic Philosophy from Its Origin to the Present: Philosophy in the Land of Prophecy]], SUNY Press, 2006, {{ISBN|0-7914-6799-6}}. page 199
* Seyyed H. Badakhchani. Contemplation and Action: The Spiritual Autobiography of a Muslim Scholar: Nasir al-Din Tusi (In Association With the Institute of Ismaili Studies. I. B. Tauris (December 3, 1999). {{ISBN|1-86064-523-2}}. page.1: ""Nasir al-Din Abu Ja`far Muhammad b. Muhammad b. Hasan Tusi:, the renowned Persian astronomer, philosopher and theologian"
* {{cite book|last1=Glick|first1=Thomas F.|author-link1=Thomas F. Glick|last2=Livesey|first2=Steven John|last3=Wallis|first3=Faith|author-link3=Faith Wallis|title=Medieval Science, Technology, and Medicine: An Encyclopedia|url=https://books.google.com/books?id=SaJlbWK_-FcC|year=2005|publisher=Psychology Press|isbn=978-0-415-96930-7|quote=drawn by the Persian cosmographer al-Tusi.}}
* {{cite book|last=Laet|first=Sigfried J. de |title=History of Humanity: From the seventh to the sixteenth century|url=https://books.google.com/books?id=PvlthkbFU1UC|year=1994|publisher=UNESCO |isbn=978-92-3-102813-7|page=908|quote=the Persian astronomer and philosopher Nasir al-Din Tusi.}}
* {{cite book|last=Mirchandani|first=Vinnie|title=The New Polymath: Profiles in Compound-Technology Innovations|url=https://books.google.com/books?id=v7bP_KlooLwC&pg=PA300|year=2010|publisher=John Wiley & Sons|isbn=978-0-470-76845-7|page=300|quote=Nasir. al-Din. al-Tusi: Stay. Humble. Nasir al-Din al-Tusi, the Persian polymath, talked about humility: “Anyone who does not know and does not know that he does not know is stuck forever in double ...}}
* {{Citation|last1=Ṭūsī|first1=Naṣīr al-Dīn Muḥammad ibn Muḥammad|title=Paradise of Submission: A Medieval Treatise on Ismaili Thought|date=2005|volume=5|pages=2–3|series=Ismaili Texts and Translations|place=London|publisher=I.B. Tauris in association with Institute of Ismaili Studies|isbn=1-86064-436-8|last2=Badakchani|first2=S. J.}}
* {{cite book|last1=Holt |first1=P. M. | last2= Lambton | first2=Ann K. S. |last3=Lewis |first3=Bernard |title=The Cambridge History of Islam Volume 2B, Islamic Society and Civilisation |date=1986 |publisher=Cambridge University Press |isbn=978-0-521-21949-5 |page=585 |edition=1st |quote=secondly, some very great Shi'i thinkers who were ethnically Persian, such as the Isma'ilis, Abu Hatim Razi and Sijistani in the fourth/tenth century, or the Imamis, Nasir al-DIn Tusi (seventh/thirteenth century) and 'Allama Hilli (seventh-eighth/thirteenth-fourteenth centuries) and many others, were to continue to write in Arabic.}}</ref> Nasir al-Din al-Tusi was a well published author, writing on subjects of math, engineering, [[prose]], and mysticism. Additionally, al-Tusi made several scientific advancements. In [[astronomy]], al-Tusi created very accurate tables of [[planetary motion]], an updated planetary model, and critiques of [[Ptolemaic astronomy]]. He also made strides in [[logic]], mathematics but especially trigonometry, biology, and chemistry. Nasir al-Din al-Tusi left behind a great legacy as well. Tusi is widely regarded as one of the greatest scientists of medieval Islam,<ref>{{Cite book|last=Brummelen|first=Glen Van|url=https://books.google.com/books?id=bHD8IBaYN-oC&q=al-kashi+law+of+cosines&pg=PA182|title=The Mathematics of the Heavens and the Earth: The Early History of Trigonometry|date=2009|publisher=Princeton University Press|isbn=978-0-691-12973-0|page=187|quote=Few would argue against the claim that al-Tusi was one of the greatest scientists of medieval Islam.}}</ref> since he is often considered the creator of [[trigonometry]] as a mathematical discipline in its own right.<ref>{{Cite web|url=http://www-history.mcs.st-andrews.ac.uk/Biographies/Al-Tusi_Nasir.html|title=Al-Tusi_Nasir biography|website=www-history.mcs.st-andrews.ac.uk|access-date=2018-08-05|quote=One of al-Tusi's most important mathematical contributions was the creation of trigonometry as a mathematical discipline in its own right rather than as just a tool for astronomical applications. In Treatise on the quadrilateral al-Tusi gave the first extant exposition of the whole system of plane and spherical trigonometry. This work is really the first in history on trigonometry as an independent branch of pure mathematics and the first in which all six cases for a right-angled spherical triangle are set forth.}}</ref><ref>{{Cite book|url=https://www.cambridge.org/core/books/the-cambridge-history-of-science/islamic-mathematics/4BF4D143150C0013552902EE270AF9C2|title=the cambridge history of science|chapter=Islamic Mathematics |year=2013 |volume=2 |pages=62–83 |publisher=Cambridge University Press |doi=10.1017/CHO9780511974007.004 |isbn=978-0-521-59448-6 |last1=Berggren |first1=J. L. }}</ref><ref>{{Cite web|url=http://www.iranicaonline.org/articles/tusi-nasir-al-din-bio|title=ṬUSI, NAṢIR-AL-DIN i. Biography – Encyclopaedia Iranica|last=electricpulp.com|website=www.iranicaonline.org|access-date=2018-08-05|quote=His major contribution in mathematics (Nasr, 1996, pp. 208–14) is said to be in trigonometry, which for the first time was compiled by him as a new discipline in its own right. Spherical trigonometry also owes its development to his efforts, and this includes the concept of the six fundamental formulas for the solution of spherical right-angled triangles.}}</ref> The  Muslim scholar [[Ibn Khaldun]] (1332–1406) considered Tusi to be the greatest of the later Persian scholars.<ref name="Khaldun">James Winston Morris, "An Arab Machiavelli? Rhetoric, Philosophy and Politics in Ibn Khaldun’s Critique of Sufism", Harvard Middle Eastern and Islamic Review 8 (2009), pp 242–291. [http://escholarship.bc.edu/cgi/viewcontent.cgi?article=1032&context=james_morris] {{Webarchive|url=https://web.archive.org/web/20100620223200/http://escholarship.bc.edu/cgi/viewcontent.cgi?article=1032&context=james_morris|date=2010-06-20}} excerpt from page 286 (footnote 39): "Ibn Khaldun’s own personal opinion is no doubt summarized in his pointed remark (Q 3: 274) that Tusi was better than any other later Iranian scholar". Original Arabic: Muqaddimat Ibn Khaldūn : dirāsah usūlīyah tārīkhīyah / li-Aḥmad Ṣubḥī Manṣūr-al-Qāhirah : Markaz Ibn Khaldūn : Dār al-Amīn, 1998. {{ISBN|977-19-6070-9}}. Excerpt from Ibn Khaldun is found in the section: الفصل الثالث و الأربعون: في أن حملة العلم في الإسلام أكثرهم العجم (On how the majority who carried knowledge forward in Islam were Persians) In this section, see the sentence where he mentions Tusi as  more knowledgeable than other later Persian ('Ajam) scholars: . و أما غيره من العجم فلم نر لهم من بعد الإمام ابن الخطيب و نصير الدين الطوسي كلاما يعول على نهايته في الإصابة. فاعتير ذلك و تأمله تر عجبا في أحوال الخليقة. و الله يخلق ما بشاء لا شريك له الملك و له الحمد و هو على كل شيء قدير و حسبنا الله و نعم الوكيل و الحمد لله.</ref> There is also reason to believe that he may have influenced [[Copernican heliocentrism]].<ref name=":12">{{Cite journal|last=Nosonovsky|first=Michael|date=2018-08-14|title=Abner of Burgos: The Missing Link between Nasir al-Din al-Tusi and Nicolaus Copernicus?|journal=Zutot|volume=15|issue=1|pages=25–30|doi=10.1163/18750214-12151070}}</ref><ref name=":22">{{Cite journal|last=Morrison|first=Robert|date=March 2014|title=A Scholarly Intermediary between the Ottoman Empire and Renaissance Europe|journal=Isis|volume=105|issue=1|pages=32–57|doi=10.1086/675550|pmid=24855871}}{{Dead link|date=January 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name=":32">{{Cite book|last=Pedersen|first=Olaf|url=https://books.google.com/books?id=z7M8AAAAIAAJ|title=Early Physics and Astronomy: A Historical Introduction|date=1993-03-11|publisher=CUP Archive|isbn=978-0-521-40899-8|pages=273–274}}</ref><ref name=":62">{{Cite web|last=Rabin|first=Sheila|date=2004-11-30|title=Nicolaus Copernicus|url=https://plato.stanford.edu/entries/copernicus/|website=[[Stanford Encyclopedia of Philosophy]]}}</ref><ref name=":03">{{Cite journal|last=Hartner|first=Willy|date=1973|title=Copernicus, the Man, the Work, and Its History|journal=Proceedings of the American Philosophical Society|volume=117|issue=6|pages=413–422|jstor=986460 |bibcode=1973PAPhS.117..413H }}</ref><ref name=":72">{{Cite journal|last=Kennedy|first=E. S.|date=October 1966|title=Late 0Medieval Planetary Theory|journal=Isis|volume=57|issue=3|pages=365–378|doi=10.1086/350144}}</ref>

==Biography==
Nasir al-Din Tusi was born in the city of [[Tus, Iran|Tus]] in [[Middle Ages|medieval]] [[Greater Khorasan|Khorasan]] (northeastern [[Iran]]) in the year 1201 and began his studies at an early age. In [[Hamadan]] and Tus, he studied the [[Quran]], [[Hadith]], [[Ja'fari jurisprudence]], logic, philosophy, mathematics, medicine, and astronomy.<ref name="Dabashi">Dabashi, Hamid. "Khwajah Nasir al-Din Tusi: The philosopher/vizier and the intellectual climate of his times". Routledge History of World Philosophies. Vol I. History of Islamic Philosophy. Seyyed Hossein Nasr and Oliver Leaman (eds.) London: Routledge. 1996. p. 529</ref>

He was born into a [[Shia Islam|Shī‘ah]] family and lost his father at a young age. Fulfilling the wish of his father, the young Nasir took learning and scholarship very seriously and traveled far and wide to attend the lectures of renowned scholars and acquired knowledge, an exercise highly encouraged in his Islamic faith. At a young age, he moved to [[Nishapur]] to study philosophy under Farid al-Din Damad and mathematics under [[Muhammad Hasib]].<ref name="HistMuslimPhil">Siddiqi, Bakhtyar Husain. "Nasir al-Din Tusi". A History of Islamic Philosophy. Vol 1. M. M. Sharif (ed.). Wiesbaden:: Otto Harrossowitz. 1963. p. 565</ref> He met also [[Attar of Nishapur]], the legendary [[Sufism|Sufi master]] who was later killed by  the [[Mongols]], and he attended the lectures of [[Qutb al-Din al-Misri]] – a student of [[Fakhr al-Din al-Razi|Al-Razi]].

Nasir-al-Din Tusi writes in his work, ''Desideratum of the Faithful (Maṭlūb al-muʾminīn)'',“To become people of spiritual reality, it is incumbent to fulfill the symbolic elucidation (''[[Esoteric interpretation of the Quran|ta'wīl]]'') of the seven pillars of the religious law (''[[Sharia|sharīʿat]]'')”. He also explains that fulfilling the religious law is much easier than fulfilling its spiritual interpretation.<ref name="Virani 193–227">{{Cite journal|last=Virani|first=Shafique N.|date=2018-04-16|title=Alamūt, Ismailism and Khwāja Qāsim Tushtarī's Recognizing God|journal=Shii Studies Review|volume=2|issue=1–2|pages=193–227|doi=10.1163/24682470-12340021}}</ref>

He explains in his book ''Aghaz u anjam'' that the sacred accounts of history that we perceive within the bounds of space and time symbolize events that have no such restrictions. They are only expressed in this way so that humans are able to comprehend them.<ref name=":1">{{Cite journal|last=Virani|first=Shafique|title=Hierohistory in Qāḍī l-Nuʿmān's Foundation of Symbolic Interpretation (Asās al-Taʾwīl): The Birth of Jesus |url=https://www.academia.edu/41992496 |journal=Studies in Islamic Historiography|year=2019 |pages=147–169 |doi=10.1163/9789004415294_007 |isbn=978-90-04-41529-4 }}</ref>

In [[Mosul]], al-Tusi studied mathematics and astronomy with [[Kamal al-Din ibn Yunus]] (d. [[Hijri year|AH]] 639 / AD 1242), a pupil of [[Sharaf al-Dīn al-Ṭūsī]].<ref name=MacT>{{Cite web|url=https://mathshistory.st-andrews.ac.uk/Biographies/Al-Tusi_Sharaf/|title=Sharaf al-Din al-Tusi – Biography|website=Maths History}}</ref> Later on he corresponded with [[Sadr al-Din al-Qunawi]], the son-in-law of [[Ibn Arabi]], and it seems that mysticism, as propagated by Sufi masters of his time, was not appealing to him. Once the occasion was suitable, he composed his own manual of philosophical Sufism in the form of a small booklet entitled ''Awsaf al-Ashraf,'' or "The Attributes of the Illustrious".

As the armies of [[Genghis Khan]] swept his homeland, he was employed by the [[Nizari Ismaili state]] and, while moving from stronghold to stronghold, made his most important contributions in science,<ref>Peter Willey, ''The Eagle's Nest: Ismaili Castles in Iran and Syria'', (I.B. Tauris, 2005), 172.</ref> first in those of the [[Quhistan]] region under ''muhtasham'' [[Nasir al-Din Abu al-Fath Abd al-Rahim ibn Abi Mansur]] (where he wrote the ''[[Nasirean Ethics]]'' in 1235). He was later sent to the major castles of [[Alamut Castle|Alamut]] and [[Maymun-Diz]] to continue his career under Nizari Imam [[Muhammad III of Alamut|Ala al-Din Muhammad]].<ref>{{cite web |author=Farhad Daftari |title=اسماعیلیان سده‌های میانه در سرزمین‌های ایران {{!}} The Institute of Ismaili Studies |url=http://akdn2stg.prod.acquia-sites.com/sites/default/files/The%20mediaeval%20Ismailis%20of%20the%20Iranian%20Lands%20-%20Farsi-103105894.pdf |website=www.iis.ac.uk |access-date=31 March 2020 }}{{Dead link|date=January 2022 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite book |last1=Lagerlund |first1=Henrik |title=Encyclopedia of Medieval Philosophy: Philosophy Between 500 and 1500 |date=2010 |publisher=Springer Science & Business Media |isbn=978-1-4020-9728-7 |page=825 }}</ref> He was captured after the [[siege of Maymun-Diz|capitulation of Maymun-Diz]] to the Mongol forces under [[Hulegu Khan]], a grandson of Genghis Khan.<ref>[[Michael Axworthy]], ''A History of Iran: Empire of the Mind'', (Basic Books, 2008), 104.</ref>

Nasir al-Din Tusi’s autobiography, ''The Voyage (Sayr wa-Suluk)'' explains that a literary devastation such as the devastation of the [[Nizari Ismaili state|Alamut]] libraries in 1256 would not waver the spirit of the [[Nizari Isma'ilism|Nizari Ismaili]] community because they give more importance to the “living book” (the [[Imamate in Ismaili doctrine|Imam of the Time]]) rather than the “[[Quran|written word]]”. Their hearts are attached to the Commander of the Believers (''[[Amir al-Mu'minin|amir al-mu'minin]]''), not just the “command” itself. There is always a present living Imam in world, and following him, a believer will never go astray.<ref name=":0">{{Citation|last=Virani|first=Shafique N.|chapter=Salvation and Imamate|date=2007-04-01|title=The Ismailis in the Middle Ages|pages=165–182|publisher=Oxford University Press|doi=10.1093/acprof:oso/9780195311730.003.0009|isbn=978-0-19-531173-0}}</ref>

=== Role during the Mongol invasion of Baghdad ===
In 1256, al-Tusi was in the castle of Alamut when it was attacked by the forces of the Mongol leader Hulegu. Some sources claim that al-Tusi betrayed the defences of Alamut to the invading Mongols. After his forces destroyed Alamut, Hulegu, who was himself interested in the natural sciences, treated al-Tusi with great respect, appointing him as scientific adviser and a permanent member of his inner council.<ref>{{Cite journal |last=VAKILY |first=ABDOLLAH |date=2001 |title=Khvājah Naṣīr al-Dīn Ṭūsī's "Āghāz va Anjām": An Introduction and Abridged Translation |url=https://www.jstor.org/stable/20837076 |journal=Islamic Studies |volume=40 |issue=1 |pages=89–103 |doi=10.52541/isiri.v40i1.5053 |jstor=20837076 |issn=0578-8072}}</ref> To great controversy, it is widely assumed Tusi was with the Mongol forces under Hulegu when they [[Siege of Baghdad|attacked]] and massacred the inhabitants of Baghdad in 1258<ref name="auto">{{Cite web |title=Nasir al-Din al-Tusi - Biography |url=https://mathshistory.st-andrews.ac.uk/Biographies/Al-Tusi_Nasir/ |access-date=2022-07-04 |website=Maths History }}</ref> and he played an essential role in ending of the Abbasid [[Caliphate|empire]].<ref>{{cite book |last1=Khandmir |first1=Ghiyasoddin ibn Homamoddin |title=The history of Habib al Sir |date=2001 |publisher=Khayyaam |location=Tehran |isbn=964-6101-53-4 |page=338 |url=https://noorlib.ir/book/view/11207}}</ref><ref>{{cite book |last1=Khansari |first1=Mohammad Bagher |title=Rozat al Jannaat |trans-title=Gardens of Paradise |date=1970–1971 |publisher=Esma'ilian |location=Ghom |page=315 |url=https://lib.eshia.ir/10983 |language=ar}}</ref><ref>{{cite book |last1=Modarresi |first1=Mohammad |title=The biography and philosophical ideas of Khawja Nasir al-Din Tus |date=2001 |publisher=Amir Kabir |location=Tehran |isbn=978-964-00-0677-1 |page=52}}</ref>
After the siege of Baghdad, he was entrusted with the administration of religious endowments and traveled extensively to both Sunni and Shiʿi institutions. In this capacity, he is credited with helping preserve religious foundations, libraries, and scholarly institutions during the period of Mongol rule.<ref name="auto"/><ref>{{Citation |last1=Strothmann |first1=R. |title=al-Ṭūsī |date=2012-04-24 |url=https://referenceworks.brillonline.com/entries/encyclopaedia-of-islam-1/al-tusi-COM_0209?s.num=1&s.f.s2_parent=s.f.book.encyclopaedia-of-islam-1&s.q=Na%E1%B9%A3%C4%ABr+al-D%C4%ABn+al-%E1%B9%AC%C5%ABs%C4%AB |encyclopedia=Encyclopaedia of Islam, First Edition (1913–1936) |publisher=Brill  |access-date=2022-07-04 |last2=Ruska |first2=J.}}</ref> Through his scholarly and administrative influence, al-Tusi helped strengthen Twelver Shiʿi intellectual life and institutional presence in Persia and Iraq, without formally transforming the sectarian order of the state.<ref>{{Cite book |last=BLACK |first=ANTONY |url=https://www.jstor.org/stable/10.3366/j.ctt1g0b63h |title=The History of Islamic Political Thought: From the Prophet to the Present |date=2011 |publisher=Edinburgh University Press |isbn=978-0-7486-3986-1 |edition=NED - New edition, 2 |jstor=10.3366/j.ctt1g0b63h }}</ref>

==Works==
Tusi has about 150 works, of which 25 are in [[Persian language|Persian]] and the remaining are in [[Arabic language|Arabic]],<ref name="H. Daiber, F.J. Ragep 2007"/> and there is one treatise in Persian, Arabic and [[Oghuz languages|Turkish]].<ref>Seyyed Hossein Nasr. The Islamic Intellectual Tradition in Persia. Curson Press, 1996. See p. 208: "Nearly 150 treatises and letters by Nasir al-Din al-Tusi are known, of which twenty-five are in Persian and the rest in Arabic. There is even a treatise on geomancy that Tusi wrote in Arabic, Persian, and Turkish, demonstrating his mastery of all three languages. It is said that he also knew Greek. His writings concern nearly every branch of the Islamic sciences, from astronomy to  philosophy and from the occult sciences to theology."</ref>
[[File:Tusi manus.jpg|thumb|right|A Treatise on the [[Astrolabe]] by Tusi, Isfahan 1505]]
* ''Sayr wa-Suluk (The Voyage)'' – Autobiography<ref name=":0" />
* ''Kitāb al-Shakl al-qattāʴ'' – Book on the complete quadrilateral. A five-volume summary of trigonometry.
* ''Al-Tadhkirah fi'ilm al-hay'ah'' – A memoir on the science of astronomy. Many commentaries were written about this work called Sharh al-Tadhkirah (A Commentary on al-Tadhkirah) – Commentaries were written by [[al-Birjandi|Abd al-Ali ibn Muhammad ibn al-Husayn al-Birjandi]] and by [[Nazzam Nishapuri]].
* ''[[Akhlaq-i Nasiri]]'' – A work on ethics.
* ''al-Risalah al-Asturlabiyah'' – A Treatise on the astrolabe.
* ''[[Zij-i Ilkhani]]'' (''Ilkhanic Tables'') – A major astronomical treatise, completed in 1272.
* ''[[Sharh al-Isharat]]'' (''Commentary on Avicenna's Isharat'')
* ''[[Awsaf al-Ashraf]]'' – a short mystical-ethical work in Persian.<ref>{{cite journal |last1=Lameer |first1=Joep |title=A New Look at Ṭūsī's Awṣāf al-ashrāf |journal=Journal of Islamic Manuscripts |date=29 April 2020 |volume=11 |issue=1 |pages=1–27 |doi=10.1163/1878464X-01101001 }}</ref>
* ''[[Tajrīd al-Iʿtiqād]]'' (Summation of Belief) – A commentary on Shi'a doctrines.
* ''[[Talkhis al-Muhassal]]'' (summary of summaries).
* ''Maṭlūb al-muʾminīn'' (Desideratum of the Faithful)<ref name="Virani 193–227"/>
* ''Aghaz u anjam'' – Esoteric interpretation of the Quran<ref name=":1" />

An example from one of his poems:
<blockquote>
Anyone who knows, and knows that he knows,<br />
makes the steed of intelligence leap over the vault of heaven.<br />
Anyone who does not know but knows that he does not know,<br />
can bring his lame little donkey to the destination nonetheless.<br />
Anyone who does not know, and does not know that he does not know,<br />
is stuck forever in double ignorance.<br />
</blockquote>

==Achievements==
[[File:Tusi couple.jpg|thumb|right|[[Tusi couple]] from Vat. Arabic ms 319]]
[[File:Tusi-couple.gif|right|thumb|220 px|[[Tusi couple]]]]

During his stay in Nishapur, Tusi established a reputation as an exceptional scholar. Tusi’s prose writing, which numbers over 150 works, represent one of the largest collections by a single Islamic author. Writing in both [[Arabic]] and [[Persian language|Persian]], Nasir al-Din Tusi dealt with both religious ("Islamic") topics and non-religious or secular subjects ("the ancient sciences").<ref name="H. Daiber, F.J. Ragep 2007">H. Daiber, F.J. Ragep, "Tusi" in Encyclopaedia of Islam. Edited by: P. Bearman, Th. Bianquis, C.E. Bosworth, E. van Donzel and W.P. Heinrichs. Brill, 2007. Brill Online. Quote: "Tusi's prose writings, which number over 150 works, represent one of the largest collections by a single Islamic author. Writing in both Arabic and Persian, Nasir al-Din dealt with both religious ("Islamic") topics and non-religious or secular subjects ("the ancient sciences")."</ref> His works include the definitive Arabic versions of the works of [[Euclid]], [[Archimedes]], [[Ptolemy]], [[Autolycus]], and [[Theodosius of Bithynia]].<ref name="H. Daiber, F.J. Ragep 2007"/>

===Astronomy===
{{further|Zij-i Ilkhani|Tusi couple}}
[[File:Nasir al-Din al-Tusi at observatory.jpg|thumb|The Astronomical Observatory of Nasir al-[[Dīn]] Tusi.]]
Tusi convinced [[Hulegu Khan]] to construct an observatory for establishing accurate astronomical tables for better astrological predictions. Beginning in 1259, the [[Maragheh observatory|Rasad Khaneh observatory]] was constructed in [[Azarbaijan]], south of the river [[Aras (river)|Aras]], and to the west of [[Maragheh]], the capital of the [[Ilkhanate|Ilkhanate Empire]].<ref name="Rossabi2014">{{cite book|author=Morris Rossabi|title=From Yuan to Modern China and Mongolia: The Writings of Morris Rossabi|url=https://books.google.com/books?id=GXejBQAAQBAJ&pg=PA281|date=28 November 2014|publisher=BRILL|isbn=978-90-04-28529-3|pages=281–}}</ref>

Based on the observations in this for the time being most advanced observatory, Tusi made very accurate tables of [[Ephemeris|planetary movements]] as depicted in his book ''[[Zij-i ilkhani]]'' (''Ilkhanic Tables''). This book contains astronomical tables for calculating the positions of the planets and the names of the stars. His model for the planetary system is believed to be the most advanced of his time, and was used extensively until the development of the heliocentric model in the time of [[Nicolaus Copernicus]]. Between [[Ptolemy]] and [[Copernicus]], he is considered by many{{who|date=April 2014}} to be one of the most eminent astronomers of his time. His famous student [[Shams al-Din al-Bukhari]]<ref name="Shams"/> was the teacher of [[Byzantine]] scholar [[Gregory Chioniades]],<ref name="Chioniadis">{{MathGenealogy|id=201288}}</ref> who had in turn trained [[astronomer]] [[Manuel Bryennios]]<ref name="Bryennios">{{MathGenealogy|id=184632}}</ref> about 1300 in [[Constantinople]].

For his planetary models, he invented a geometrical technique called a [[Tusi-couple]], which generates linear motion from the sum of two circular motions. He used this technique to replace [[Ptolemy]]'s problematic [[equant]]<ref>Craig G. Fraser, '[https://books.google.com/books?id=3tJr_vl6rYsC&pg=PA39 The cosmos: a historical perspective]', Greenwood Publishing Group, 2006 p.39</ref> for many planets, but was unable to find a solution to Mercury, which was used later by [[Ibn al-Shatir]] as well as [[Ali Qushji]].<ref>George Saliba, '[https://www.academia.edu/22220405/Al_Qushj%C4%ABs_Reform_of_the_Ptolemaic_Model_for_Mercury]', Arabic Sciences and Philosophy, v.3 1993, pp.161–203</ref>  The Tusi couple was later employed in [[Ibn al-Shatir]]'s [[geocentric model]] and [[Nicolaus Copernicus]]' [[Heliocentrism|heliocentric]] [[Copernican heliocentrism|Copernican model]].<ref>George Saliba, 'Revisiting the Astronomical Contacts Between the World of Islam and Renaissance Europe: The Byzantine Connection', '[https://books.google.com/books?id=muGVUiKEYccC&pg=PA368 The occult sciences in Byzantium]', 2006, p.368</ref> He also calculated the value for the annual precession of the [[equinox]]es and contributed to the construction and usage of some astronomical instruments including the [[astrolabe]].

Ṭūsī criticized Ptolemy's use of observational evidence to show that the Earth was at rest, noting that such proofs were not decisive. Although it doesn't mean that he was a supporter of mobility of the earth, as he and his 16th-century commentator [[al-Birjandi|al-Bīrjandī]], maintained that the earth's immobility could be demonstrated, only by physical principles found in natural philosophy.<ref>{{Citation | last = Ragep | first = F. Jamil | title = Freeing Astronomy from Philosophy: An Aspect of Islamic Influence on Science | journal = Osiris | volume = 16, 2nd ser. | pages = 49–64 | date = 2001 | jstor = 301979 | doi=10.1086/649338 | url = https://escholarship.mcgill.ca/concern/articles/m326m556v }}, at p. 60.</ref> Tusi's criticisms of Ptolemy were similar to the arguments later used by Copernicus in 1543 to defend the Earth's rotation.<ref>F. Jamil Ragep (2001), "Tusi and Copernicus: The Earth's Motion in Context", ''Science in Context'' '''14''' (1–2), p. 145–163. [[Cambridge University Press]].</ref>

About the real essence of the Milky Way, Ṭūsī in his ''Tadhkira'' writes:
"The Milky Way, i.e. the galaxy, is made up of a very large number of small, tightly-clustered stars, which, on account of their concentration and smallness, seem to be cloudy patches. because of this, it was likened to milk in color."
<ref>Ragep, Jamil, ''Nasir al-Din Tusi’s Memoir on Astronomy'' (''al-Tadhkira fi `ilm al-hay’ a'') Edition, Translation, Commentary, and Introduction. 2 vols. Sources in the History of Mathematics and Physical Sciences. New York: Springer-Verlag, 1993. pp. 129</ref>
Three centuries later the proof of the Milky Way consisting of many stars came in 1610 when [[Galileo Galilei]] used a [[Optical telescope|telescope]] to study the Milky Way and discovered that it is really composed of a huge number of faint stars.<ref>{{cite web | author = O'Connor, J. J. | author2 = Robertson, E. F. | date = November 2002 | url = http://www-gap.dcs.st-and.ac.uk/~history/Biographies/Galileo.html | title = Galileo Galilei | publisher = University of St Andrews | access-date = 2007-01-08 | archive-date = 2012-05-30 | archive-url = https://archive.today/20120530/http://www-gap.dcs.st-and.ac.uk/~history/Biographies/Galileo.html | url-status = dead }}</ref>

===Logic===
Nasir al-Din Tusi was a supporter of [[Avicennian logic]], and wrote the following commentary on [[Avicenna]]'s theory of absolute [[proposition]]s:

{{blockquote|"What spurred him to this was that in the [[assertoric]] [[syllogistic]] [[Aristotle]] and others sometimes used [[Contradiction|contradictories]] of absolute propositions on the assumption that they are absolute; and that was why so many decided that absolutes did contradict absolutes. When Avicenna had shown this to be wrong, he wanted to develop a method of construing those examples from Aristotle."<ref name=Stanford>{{cite web|author=Tony Street|title=Arabic and Islamic Philosophy of Language and Logic|publisher=[[Stanford Encyclopedia of Philosophy]]|date=July 23, 2008|url=http://plato.stanford.edu/entries/arabic-islamic-language|access-date=2008-12-05}}</ref>}}

===Mathematics===
[[File:Stamps of Azerbaijan, 2009-861.jpg|thumb|upright|A stamp issued in the republic of Azerbaijan in 2009 honoring Tusi]]
Al-Tusi was the first to write a work on trigonometry independently of astronomy.<ref name=britannica>{{cite encyclopedia|title=trigonometry|url=https://www.britannica.com/EBchecked/topic/605281/trigonometry|encyclopedia=[[Encyclopædia Britannica]]|access-date=2011-04-25}}</ref> Al-Tusi, in his ''Treatise on the Quadrilateral'', gave an extensive exposition of [[spherical trigonometry]], distinct from astronomy.<ref>[[Victor J. Katz|Katz, Victor J.]] (1993). ''A History of Mathematics: An Introduction'', p259. [[Addison Wesley]]. {{ISBN|0-673-38039-4}}.</ref> It was in the works of Al-Tusi that trigonometry achieved the status of an independent branch of pure mathematics distinct from astronomy, to which it had been linked for so long.<ref>{{cite book|last=Bosworth|first=Clifford E.|title=History of civilizations of Central Asia.|date=2003|publisher=Motilal Banarsidass|isbn=81-208-1596-3|author2=Asimov|volume=4|page=190}}</ref><ref>{{cite book|last=Hayes|first=John R.|title=The genius of Arab civilization : source of Renaissance|date=1983|publisher=Taylor & Francis|isbn=0-262-08136-9|edition=2nd|author2=Badeau, John S.|page=156}}</ref>

He was the first to list the six distinct cases of a right triangle in spherical trigonometry.<ref>http://www-history.mcs.st-andrews.ac.uk/Biographies/Al-Tusi_Nasir.html,"One{{Dead link|date=April 2020 |bot=InternetArchiveBot |fix-attempted=yes }} of al-Tusi's most important mathematical contributions was the creation of trigonometry as a mathematical discipline in its own right rather than as just a tool for astronomical applications. In Treatise on the quadrilateral al-Tusi gave the first extant exposition of the whole system of plane and spherical trigonometry. This work is really the first in history on trigonometry as an independent branch of pure mathematics and the first in which all six cases for a right-angled spherical triangle are set forth"/</ref>

This followed earlier work by [[Greek mathematics|Greek mathematicians]] such as [[Menelaus of Alexandria]], who wrote a book on spherical trigonometry called ''Sphaerica'', and the earlier Muslim mathematicians [[Abū al-Wafā' al-Būzjānī]] and [[Al-Jayyani]].

In his ''On the Sector Figure'', appears the famous [[law of sines|Sine Law]] for plane triangles.<ref name=Berggren-518>{{cite book | first=J. Lennart | last=Berggren | title=The Mathematics of Egypt, Mesopotamia, China, India, and Islam: A Sourcebook | chapter=Mathematics in Medieval Islam | publisher=Princeton University Press | date=2007 |isbn=978-0-691-11485-9 | page=518}}</ref>

:<math> \frac{a}{\sin A} = \frac{b}{\sin B} = \frac{c}{\sin C} </math>

He also stated the sine law for spherical triangles,<ref>''Also the 'sine law' (of geometry and trigonometry, applicable to spherical trigonometry) is attributed, among others, to Alkhujandi. (The three others are Abul Wafa Bozjani, Nasiruddin Tusi, and Abu Nasr Mansur).'' Razvi, Syed Abbas Hasan (1991) ''A history of science, technology, and culture in Central Asia, Volume 1'' University of Peshawar, Peshawar, Pakistan, page 358, {{OCLC|26317600}}</ref><ref>Bijli suggests that three mathematicians are in contention for the honor, Alkhujandi, Abdul-Wafa and Mansur, leaving out Nasiruddin Tusi. Bijli, Shah Muhammad and Delli, Idarah-i Adabiyāt-i (2004) ''Early Muslims and their contribution to science: ninth to fourteenth century'' Idarah-i Adabiyat-i Delli, Delhi, India, page 44, {{OCLC|66527483}}</ref> discovered the [[law of tangents]] for spherical triangles, and provided proofs for these laws.<ref name=Berggren-518/>

=== [[Color theory]] ===
While Aristotle (d. 322 BCE) had suggested that all colors can be aligned on a single line from black to white, Ibn-Sina (d. 1037) described that there were three paths from black to white, one path via grey, a second path via red and the third path via green. Al-Tusi (ca. 1258) stated that there are no less than five of such paths, via lemon (yellow), blood (red), pistachio (green), indigo (blue) and grey. This text, which was copied in the Middle East numerous times until at least the nineteenth century as part of the textbook Revision of the Optics (Tanqih al-Manazir) by [[Kamāl al-Dīn al-Fārisī#Optics|Kamal al-Din al-Farisi]] (d. 1320), made [[color space]] effectively two-dimensional.<ref>{{cite journal |last1=Kirchner |first1=E. |title=Color theory and color order in medieval Islam: A review |journal=Color Research & Application |date=2013 |volume=40 |issue=1 |pages=5–16 |doi=10.1002/col.21861}}</ref> 
Before Al-Tusi, Robert Grosseteste (d. 1253) had proposed an effectively three-dimensional model of color space.<ref>{{cite journal |last1=Smithson |first1=H.E. |last2=Dinkova-Bruun |first2=G. |last3=Gasper |first3=G.E.M. |last4=Huxtable |first4=M. |last5=McLeish |first5=T.C.B. |last6=Panti |first6=C. |title=A three-dimensional color space from the 13th century |journal=J. Opt. Soc. Am. A |date=2012 |volume=29 |issue=2 |pages=A346-52 |doi=10.1364/josaa.29.00A346|pmid=22330399 |pmc=3287286 |bibcode=2012JOSAA..29A.346S }}</ref>

===Biology===
In his ''Akhlaq-i Nasiri'', Tusi wrote about several biological topics. He defended a version of Aristotle's ''[[scala naturae]]'', in which he placed man above animals, plants, minerals, and the elements. He described "grasses which grow without sowing or cultivation, by the mere mingling of elements,"<ref name="NEp44">Nasir ad-Din Tusi (1964) ''The Nasirean Ethics'' (translator: G.M. Wickens). London: Allen & Unwin, p.&nbsp;44.</ref> as closest to minerals. Among plants, he considered the [[date-palm]] as the most highly developed, since "it only lacks one thing further to reach (the stage of) an animal: to tear itself loose from the soil and to move away in the quest for nourishment."<ref name="NEp44" />

The lowest animals "are adjacent to the region of plants: such are those animals which propagate like grass, being incapable of mating [...], e.g. [[earthworm]]s, and certain [[insect]]s".<ref>Nasir ad-Din Tusi (1964) ''The Nasirean Ethics'' (translator: G.M. Wickens). London: Allen & Unwin, p.&nbsp;45.</ref> The animals "which reach the stage of perfection [...] are distinguished by fully developed weapons", such as antlers, horns, teeth, and claws. Tusi described these organs as adaptations to each species's lifestyle, in a way anticipating [[natural theology]]. He continued:

{{blockquote|"The noblest of the species is that one whose sagacity and perception is such that it accepts discipline and instruction: thus there accrues to it the perfection not originally created in it. Such are the schooled [[horse]] and the trained [[falcon]]. The greater this faculty grows in it, the more surpassing its rank, until a point is reached where the (mere) observation of action suffices as instruction: thus, when they see a thing, they perform the like of it by mimicry, without training [...]. This is the utmost of the animal degrees, and the first of the degrees of Man in contiguous therewith."<ref>Nasir ad-Din Tusi (1964) ''The Nasirean Ethics'' (translator: G.M. Wickens). London: Allen & Unwin, p.&nbsp;45f.</ref>}}

Thus, in this paragraph, Tusi described different types of [[learning]], recognising [[observational learning]] as the most advanced form, and correctly attributing it to certain animals.

Tusi seems to have perceived man as belonging to the animals, since he stated that "the Animal Soul [comprising the faculties of perception and movement ...] is restricted to individuals of the animal species", and that, by possessing a "Human Soul, [...] mankind is distinguished and particularized among ''other'' animals."<ref>Nasir ad-Din Tusi (1964) ''The Nasirean Ethics'' (translator: G.M. Wickens). London: Allen & Unwin, p.&nbsp;42 (emphasis added).</ref>

Some scholars have interpreted Tusi's biological writings as suggesting that he adhered to some kind of [[evolution]]ary theory. However, Tusi did not state explicitly that he believed species to change over time.{{citation needed|date=June 2023}}

===Chemistry===
Tusi contributed to the field of chemistry, stating an early law of [[conservation of mass]]. Al-Tusi's theory of chemical transformation was based on the idea that substances could be transformed into other substances through chemical reactions, but that the total mass of the substances involved in the reaction would remain constant. This idea was a precursor to the law of conservation of mass, which states that the total mass of a closed system remains constant during a chemical reaction. Al-Tusi believed that chemical transformations were governed by natural laws and that they could be understood through observation, experimentation, and logical reasoning.<ref>Ahmad Y. al-Hassan, ''Conservation of Mass in Fourteenth Century Chemistry'', History of Science, vol. 17, pp. 65–80, 1979.</ref><ref>Abdelhamid I. Sabra, ''The Development of the Concept of Mass in the Arabic-Islamic Golden Age: Physics, Metaphysics, and Chemistry'', Archiv für Geschichte der Philosophie, vol. 84, no. 2, pp. 115–136, 2002</ref><ref>Roshdi Rashed, ''Nasir al-Din al-Tusi and the Problem of the Equilibrium of Weights'', Arabic Sciences and Philosophy, vol. 1, no. 2, pp. 165–183, 1991.</ref>

=== Philosophy ===
Tusi contributed many writings to the topic of philosophy. Amongst his philosophical work are his disagreements with fellow philosopher [[Avicenna]]. His most famous philosophical work is ''[[Nasirean Ethics|Akhlaq-i nasiri]]'' or ''[[Nasirean Ethics]]'' in English.<ref name="Freely 2011">{{Cite book|last=Freely|first=John|date=2011|title=Light from the East|url=http://dx.doi.org/10.5040/9780755600007|doi=10.5040/9780755600007|isbn=978-0-7556-0000-7}}</ref> Within this work he discusses and compares Islamic teachings to the ethics of Aristotle and Plato. Tusi's book became a popular ethical work in the Muslim world, specifically in India and Persia.<ref name="Freely 2011"/> Tusi's work also left an impact on Shi'ite Islamic theology. His book ''Tagrid'' also called ''Catharsis'' is significant in Shi'ite theology.<ref name="bloomsburymedievalstudies.com">{{Cite book|last=Freely|first=John|url=https://www.bloomsburymedievalstudies.com/encyclopedia?docid=b-9780755600007|title=Light from the East: How the Science of Medieval Islam Helped to Shape the Western World|date=2011|publisher=I.B.Tauris|isbn=978-0-7556-0000-7|doi=10.5040/9780755600007}}</ref> He also contributed five works to the subject of logic; which were highly regarded by his contemporaries and achieved notoriety in the Muslim world.<ref name="bloomsburymedievalstudies.com"/>

==Influence and legacy==
A 60-km diameter lunar [[Impact crater|crater]] located on the southern hemisphere of the [[moon]] is named after him as "[[Nasireddin (crater)|Nasireddin]]". A [[minor planet]] [[10269 Tusi]] discovered by [[Soviet Union|Soviet]] astronomer [[Nikolai Stepanovich Chernykh]] in 1979 is named after him.<ref>{{cite journal |title=Astronomical Education in Azerbaijan: Existing Heritage Current Status and Perspectives |bibcode = 2003ASPC..289..157B |last1=Babaev |first1=E. S. |journal=The Proceedings of the IAU 8th Asian-Pacific Regional Meeting |year=2003 |volume=289 |page=157 }}</ref><ref>{{cite book|url=https://books.google.com/books?q=10269+tusi&hl=lt |title=10269 tusi – Mano biblioteka – Google knygos |access-date=2013-02-27}}</ref> The [[K. N. Toosi University of Technology]] in [[Iran]] and Observatory of Shamakhy in the [[Republic of Azerbaijan]] are also named after him. In February 2013, Google celebrated his 812th birthday with a [[Google Doodle|doodle]], which was accessible in its websites with Arabic language calling him ''al-farsi'' (the Persian).<ref name=google-doodle>{{cite web|title=Nasir al-Din al-Tusi's 812th Birthday|url=https://doodles.google/doodle/nasir-al-din-al-tusis-812th-birthday/|access-date=19 February 2013}}</ref><ref name="BBC Persian">{{cite news|title=In Persian نگاه عربی به خواجه نصیرالدین طوسی در گوگل|url=https://www.bbc.com/persian/science/2013/02/130219_l42_khaje_nasir_google|access-date=19 February 2013|date=19 February 2013}}</ref> His birthday is also celebrated as [[Engineer's Day]] in Iran.<ref>{{cite web|url=http://calendar.ut.ac.ir/|title=مرکز تقويم موسسه ژئوفيزيک دانشگاه تهران|website=calendar.ut.ac.ir|access-date=2020-02-24|archive-date=2006-02-09|archive-url=https://web.archive.org/web/20060209200905/http://calendar.ut.ac.ir/|url-status=dead}}</ref>

=== Possible influence on Copernicus ===
Some scholars believe that [[Nicolaus Copernicus]] may have been influenced by Middle Eastern astronomers due to uncanny similarities between his work and the uncited work of these Islamic scholars, including Nasir al-Din al-Tusi, [[Ibn al-Shatir]], [[Mu'ayyad al-Din al-Urdi|Muayyad al-Din al-Urdi]], and [[Qutb al-Din al-Shirazi]].<ref name=":12"/><ref name=":22"/><ref name=":32"/><ref name=":62"/><ref name=":03"/><ref name=":72"/> al-Tusi specifically, the plagiarism in question comes from similarities in the [[Tusi couple]] and [[Nicolaus Copernicus|Copernicus]]' geometric method of removing the [[Equant]] from mathematical astronomy.<ref name=":32" /><ref name=":03" /> Not only do both of the methods match geometrically, however, more importantly they both use the same exact lettering system for each [[Vertex (geometry)|vertex]]; a detail that seems too preternatural to be happenstance.<ref name=":32" /><ref name=":03" /> Moreover, the fact that several other details of his model also mirror other Islamic scholars bolsters the notion that Copernicus' work may not have been only his own.<ref name=":03" />

There is no evidence that any of the direct work of Nasir al-Din al-Tusi ever made it to Copernicus, however there is evidence that the mathematics and theories did make the journey to Europe.<ref name=":12" /><ref name=":22" /> There were Jewish scientists and pilgrims who would make the journey from the Middle East to Europe, bringing with them Middle Eastern scientific ideas to share with their Christian counterparts.<ref name=":22" /> While this is not direct evidence that Copernicus has access to al-Tusi's work, it does show that it was possible.<ref name=":22" />  There was just such a Jewish scholar by the name of  [[Abner of Burgos]] who wrote a book containing an incomplete version of the Tusi couple that he had learned second hand, which could have been found by Copernicus.<ref name=":12" /> His version had no proofs of the geometry either, so if Copernicus had obtained this book he would have had to complete both the proof and mechanism.<ref name=":12" /> Additionally, some scholars believe that, if not Jewish thinkers, it could have been transmission from the Islamic school in [[Maragheh]], home to Nasir al-Din al-Tusi's [[Maragheh observatory|observatory]] to Muslim Spain.<ref name=":12" /><ref name=":22" /> From Spain, al-Tusi and other Islamic cosmological theories could spread through Europe.<ref name=":12" /><ref name=":22" /> Spread of Islamic astronomy from Maragheh Observatory into Europe could have also been possible in the form of Greek translations from [[Gregory Choniades]].<ref name=":22" /> There is evidence as to the means of Copernicus acquiring the Tusi couple and suspicious similarities, not only in math but in visual details as well.<ref name=":12" /><ref name=":22" /><ref name=":32" /><ref name=":62" /><ref name=":03" /><ref name=":72" />

Despite this circumstantial evidence, there is still no direct proof that Copernicus did plagiarize the work of Nasir al-Din al-Tusi, and if he did that he did so intentionally.<ref name=":32" /><ref name=":4">{{Cite journal|last=Veselovsky|first=I. N.|date=1973-06-01|title=Copernicus and Nasīr Al-DĪn AL-TŪSĪ|journal=Journal for the History of Astronomy |volume=4 |issue=2 |pages=128–130 |doi=10.1177/002182867300400205 |bibcode=1973JHA.....4..128V}}</ref><ref name=":5">{{Cite journal|last=Blåsjö|first=Viktor|date=2014-04-15|title=A Critique of the Arguments for Maragha Influence on Copernicus|journal=Journal for the History of Astronomy|volume=45|issue=2|pages=183–195|doi=10.1177/002182861404500203 |bibcode=2014JHA....45..183B }}</ref><ref name=":8">{{Cite web|last=Blasjo|first=V. N. E.|date=2018|title=A rebuttal of recent arguments for Maragha influence on Copernicus|url=http://dspace.library.uu.nl/bitstream/handle/1874/374781/blasjo2.pdf?sequence=1&isAllowed=y|access-date=2020-11-17|website=Studia Historiae Scientiarum|archive-date=2021-05-06|archive-url=https://web.archive.org/web/20210506040346/http://dspace.library.uu.nl/bitstream/handle/1874/374781/blasjo2.pdf?sequence=1&isAllowed=y|url-status=dead}}</ref> The Tusi couple is not a unique principle, and as the equant was a problematic necessity to preserve circular motion it is possible that more than one astronomer wished to improve on it; to that end, some scholars argue it would not be difficult for an astronomer to use [[Euclid]]'s own work to derive the Tusi couple on their own, and that Copernicus most likely did this instead of stealing.<ref name=":4" /><ref name=":5" /> Before Copernicus ever published the work on his geometrical mechanism, he had written at length his dissatisfaction over [[Ptolemaic astronomy]] and the use of the equant, so some scholars then purport that it was not unfounded for Copernicus to have rederived the Tusi couple without having seen it as he had clear motive to do so.<ref name=":5" /> Also, some scholars that argue Copernicus did commit plagiarism say that by never claiming it as his own, he inherently condemns himself.<ref name=":8" /> However, others critique that mathematicians do not normally claim work like other scientists, so declaring a theorem for oneself is an exception and not the norm.<ref name=":8" /> Therefore, there is motive and some explanation as to why and how Copernicus did not plagiarize, despite the evidence against him.<ref name=":4" /><ref name=":5" /><ref name=":8" />

==See also==

* [[List of Iranian scientists]]
* [[List of Shi'a Muslims]]
* [[Persian science]]
* [[Science in the medieval Islamic world]]
* [[Shen Kuo]]

==Footnotes==
{{Clear}}{{Notelist}}{{reflist|30em}}

==Further reading==
* {{DSB|title=Ṭūsī, Muḥammad Ibn Muḥammad Ibn al-Ḥasan }}
* {{MacTutor|id=Al-Tusi_Nasir|title=Nasir al-Din Tusi}}
* Encyclopædia Iranica, "AḴLĀQ-E NĀṢERĪ", G.M. Wickens [https://web.archive.org/web/20110318022941/http://www.iranicaonline.org/articles/aklaq-e-naseri-by-kaa-nasir-al-din-tusi-the-principal-treatise-in-persian-on-ethics-economics-and-politics-f Encyclopædia Iranica | Articles]
* Encyclopædia Iranica, "AWṢĀF AL-AŠRĀF", G.M. Wickens [http://www.iranicaonline.org/articles/awsaf-al-asraf-a-short-mystical-ethical-work-in-persian-by-nasir-al-din-tusi-written-late-in-life-ca Welcome to Encyclopaedia Iranica]
* Encyclopædia Iranica, "Nasir al-Din Tusi" George Saliba [http://www.iranicaonline.org/articles/tusi-nasir-al-din Welcome to Encyclopaedia Iranica]

==External links==
{{external links|date=June 2021}}
* {{cite encyclopedia | editor = Thomas Hockey |display-editors=etal | last = Ragep| first = F. Jamil | title=Ṭūsī: Abū Jaʿfar Muḥammad ibn Muḥammad ibn al-Ḥasan Naṣīr al-Dīn al-Ṭūsī | encyclopedia = The Biographical Encyclopedia of Astronomers | publisher = Springer | date = 2007 |location = New York | pages = 1153–5 |url=http://islamsci.mcgill.ca/RASI/BEA/Tusi_BEA.htm |isbn=978-0-387-31022-0}} ([http://islamsci.mcgill.ca/RASI/BEA/Tusi_BEA.pdf PDF version])
* {{cite encyclopedia | last = Nasr | first = Seyyed Hossein | title=Al-Ṭūsī, Muḥammad Ibn Muḥammad Ibn Al-Ḥasan Usually Known as Naṣir Al-Dīn | url=http://www.encyclopedia.com/doc/1G2-2830904400.html | encyclopedia = [[Dictionary of Scientific Biography|Complete Dictionary of Scientific Biography]] | publisher = Encyclopedia.com | orig-year=1970–80 | date = 2008 }}
* [http://www.muslimphilosophy.com/ip/rep/H036.htm Biography] by Islamic Philosophy Online
* [http://www.iep.utm.edu/t/tusi.htm Biography] by The Internet Encyclopedia of Philosophy
* [http://www.wilbourhall.org/index.html#rekha The Rekhaganita] — An 18th-century Sanskrit translation of Nasir al-Din al-Tusi's recension of Euclid's'' Elements''
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{{Islamic astronomy}}
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{{DEFAULTSORT:Tusi, Nasir Din}}
[[Category:People from Tus, Iran]]
[[Category:Scientists who worked on qibla determination]]
[[Category:Iranian Shia scholars of Islam]]
[[Category:1201 births]]
[[Category:1274 deaths]]
[[Category:13th-century Iranian astronomers]]
[[Category:13th-century Iranian mathematicians]]
[[Category:13th-century Iranian philosophers]]
[[Category:13th-century Muslim scholars of Islam]]
[[Category:Iranian ethicists]]
[[Category:Scholars from the Ilkhanate]]
[[Category:13th-century Shia Muslims]]
[[Category:Astronomers of the medieval Islamic world]]
[[Category:People associated with astronomical catalogues]]