The Nizari Ismailis of the Alamut period: Astronomy

The Nizari Ismailis of the Alamut period: Astronomy
Tusi couple from Vat. Arabic ms 319

Nasir al-Din al-Tusi contributed to the heliocentric model of planetary motion.

Researched by Nimira Dewji

Nasir al-Din al-Tusi (1201-1274), a renowned Muslim scholar, spent three decades at Alamut writing works on astronomy, theology, philosophy, and other subjects. Historians agree that it is primarily through Al-Tusi’s extant works that they have an understanding of the Nizari Ismaili thought as it developed during the Alamut period (1090-1256). Many of Nasir’s works became the standard in a variety of disciplines. His work on astronomy, al-Tadhkira fi ‘ilm al-hay’a (Memoir on the Science of Astronomy), had an enormous influence on the subsequent history of astronomy evidenced by the significant number of extant manuscript copies of this text as well as the large number of commentaries written on the Tadhkira.

In April 2006, F. Jamil Ragep, a professor of history of science at the University of Oklahoma, delivered a lecture making the link between the theories of Copernicus in the sixteenth century, and the works of Nasir al-Din al-Tusi in the thirteenth century.  Ragep believes that Tusi’s work, carried out at Alamut as well as the observatory at Maragha (in Iran), and inventions such as the “Tusi Couple” were critical to Copernicus’s understanding of the heliocentric model of the planetary motion.

Al-Noor Merchant, Nasir al-Din al-Tusi and Astronomy. The Institute of Ismaili Studies
Norriss S. Hetherington, Planetary Motions – A Historical Perspective. Greenwood Press, Westport, 2006

Also read:

The Nizari Ismailis of the Alamut period: Libraries
The Nizari Ismailis of the Alamut period: Engineers

One thought

  1. I strongly recommend all read Ragep’s 2007 paper at the link below:


    Although not conclusive, yet, it is becoming clearer and clearer that Copernicus was heavily influenced by Muslim scientists, Tusi in particular. Indeed Copernicus used one of Tusi’s own diagrams unchanged in his own works (as can be seen in Ragep’s paper). The great “leap” Copernicus had — explained by him may not be so great, and may have already been there. Indeed there are records of Greeks having suggested the heliocentric solar system well before even the Muslims arrived on the scene.

    The issue for the Muslims was that Ptolemy’s model of the solar system did not match the observations and so the Muslims — who were at the peak of astronomy — had been working on the issue for 500 years on the issue and were closing in (if they hadn’t already) to solution. The revolutionary break through they had already made was realizing there was no need for the Earth to be stationary for their observations to still be valid. This was the real breakthrough as it went counter to 2,000 years of history and conditioning that the Earth was stationary. Once a moving Earth was allowed, a range of new possible solar system models became possible.

    Some extracts from Ragep’s paper:

    That Copernicus was acquainted with a number of his Islamic predecessors has
    been evident since 1543, when Copernicus in De revolutionibus explicitly cited five
    Islamic authors.1 The latest of these authors, al-Bitruji, flourished in Spain in the
    last part of the twelfth century, so Copernicus’s references end around 1200, which
    is the approximate terminus date for Islamic authors who were translated into Latin.
    Until recently, most historiography related to Copernicus has assumed that this was
    the end of the story, at least as far as Islamic influence goes. But since the 1950s, a
    series of discoveries has shaken this neatly constricted picture and caused a major
    re-evaluation of the relation of Copernicus (as well as other Renaissance astronomers)
    to later Islamic astronomy.

    The first modern acknowledgement of a connection between Copernicus and
    a later (i.e. post-1200) Islamic astronomer was made by J. L. E. Dreyer in 1906.
    In a footnote, Dreyer noted that the new device invented by Nasir al-Din al-Tusi
    (d. 1274) was also used by Copernicus in Book III, chap. 4 of De revolutionibus.2
    Typical for the time, Dreyer offered no further explanation or speculation; nor did
    anyone else until the discovery in the 1950s of a connection between another Islamic
    astronomer and Copernicus. E. S. Kennedy, who was a professor of mathematics
    at the American University of Beirut, happened by chance to notice some unusual
    (i.e. non-Ptolemaic) astronomical models while browsing through the Nihayat alsul
    of cAla’ al-Din Ibn al-Shatir, a Damascene astronomer of the fourteenth century
    who had been the time-keeper of the Umayyad Mosque. Upon showing these to his
    friend and mentor, Otto Neugebauer of Brown University, Kennedy was amazed to
    learn that these models were ones that had been thought to have first appeared in the
    works of Nicholas Copernicus. This led to a series of articles by Kennedy and his
    students that discussed various aspects of these models by Ibn al-Shatir as well as
    by other late Islamic astronomers.3 …


    Noel Swerdlow and Otto Neugebauer, in discussing this Islamic tradition, famously
    asked: “What does all this have to do with Copernicus?” Their answer was: “Rather
    a lot.”13 In his commentary on Copernicus’s Commentariolus, Swerdlow made the
    case for this connection through a remarkable reconstruction of how Copernicus had
    arrived at the heliocentric system. According to Swerdlow, Copernicus, somehow
    aware of this Islamic tradition of non-Ptolemaic astronomy, began his work to reform
    astronomy under its influence. In particular Copernicus objected explicitly to Ptolemy’s
    use of the equant, an objection that had been a staple of Islamic astronomy for
    some five centuries at that point (but which seems not to have been made by earlier
    European astronomers).14 Swerdlow then proposed that although Copernicus was
    able to use some of these models, in particular those of Ibn al-Shatir, to deal with
    the irregular motion brought about by the first anomaly (the motion of the epicycle
    centre on the deferent), it was the second anomaly (related to the motion of the
    planet on the epicycle) that remained problematic. For the outer planets this motion
    corresponds to the motion of the Earth around the Sun, so a transformation of this
    motion from an epicyclic to an eccentric would lead to a quasi-heliocentric system,
    whereby the planet goes around the Sun. Of course the Earth could still remain at
    rest while the Sun, with the planets going around it, could then go around the Earth.
    In other words, Copernicus’s transformations could have led to a Tychonic system.
    Swerdlow argued that this was not an option for Copernicus, since it led to the notorious
    intersection of the spheres of the Sun and Mars, which simply was not possible
    in the solid-sphere astronomy to which Copernicus was committed. Thus Copernicus
    was compelled to opt for a heliocentric system with the Earth, as a planet, in motion
    around the Sun.15

    In his reconstruction, Swerdlow assumed that Copernicus must have had access
    to the models of his Islamic predecessors. Because of the scarcity of concrete evidence
    for this assertion (i.e. translated texts in Latin, earlier European references to these
    models, or the like), Swerdlow was clearly swayed by the similarity of complex
    geometrical models; independent discovery was simply not an option. As he stated
    with Neugebauer in 1984:

    The planetary models for longitude in the Commentariolus are all based upon
    the models of Ibn ash-Shatir — although the arrangement for the inferior planets
    is incorrect — while those for the superior planets in De revolutionibus use
    the same arrangement as cUrdi’s (sic) and Shirazi’s model, and for the inferior
    planets the smaller epicycle is converted into an equivalent rotating eccentricity
    that constitutes a correct adaptation of Ibn ash-Shatir’s model. In both the Commentariolus
    and De revolutionibus the lunar model is identical to Ibn ash-Shatir’s
    and finally in both works Copernicus makes it clear that he was addressing the
    same physical problems of Ptolemy’s models as his predecessors. It is obvious
    that with regard to these problems, his solutions were the same.
    The question therefore is not whether, but when, where, and in what form he
    learned of Maragha theory.16

    This has recently been reinforced by Swerdlow:

    How Copernicus learned of the models of his [Arabic] predecessors is not
    known — a transmission through Italy is the most likely path — but the relation
    between the models is so close that independent invention by Copernicus is all
    but impossible.17

    Neugebauer and Swerdlow did have one bit of evidence that seemed to show a
    likely means of transmission between the Islamic world and Italy. This was a text
    contained in MS Vat. Gr. 211, in which one finds the Tusi couple (rectilinear version)
    and Tusi’s lunar model. Apparently dating from about 1300, it is either a Greek
    translation or reworking of an Arabic treatise, made perhaps by the Byzantine scholar
    Gregory Chioniades.18 The fact that this manuscript found its way to the Vatican,
    perhaps in the fifteenth century, provides a possible means for the transmission of
    knowledge of Tusi’s models. It is also noteworthy that Tusi’s models seem to have
    been widely known by contemporaries of Copernicus; examples include Giovanni
    Battista Amico and Girolamo Fracastoro.19

    The historian of astronomy Willy Hartner also pointed to evidence for transmission
    from Islamic astronomers to Copernicus. Though he states that independent discovery
    of these models and devices by Copernicus was “possible”, “it seems more probable
    that the news of his Islamic predecessor’s model reached him in some way or other”.
    Here Hartner was speaking of the model of Ibn al-Shatir; he was more certain that
    another example “proves clearly” the borrowing by Copernicus of the Tusi couple
    inasmuch as the lettering in Copernicus’s diagram in De revolutionibus follows the
    standard Arabic lettering rather than what one might expect in Latin.20 …


    Qushji was the son of the falconer of Ulugh Beg (1394–1449), the Timurid prince
    who was a generous patron of the sciences and arts. Ulugh Beg was an active supporter
    and participant in the magnificent Samarqand observatory, which was one of
    the greatest scientific institutions that had been established up to that time. As a boy,
    Qushji became his protégé and student and eventually occupied an important position
    at the observatory. After the assassination of Ulugh Beg, Qushji was attached to
    various courts in Iran but would end his career in Constantinople under the patronage
    of Mehmet II, who had conquered the city for the Ottomans.

    Qushji held that the astronomer had no need for Aristotelian physics and in fact
    should establish his own physical principles independently of the natural philosophers.
    39 This position had profound implications for one principle in particular, namely
    that the element earth had a principle of rectilinear inclination that precluded it from
    moving naturally with a circular motion.40 Tusi had maintained that there was no
    way for the astronomer, using mathematics and observation, to arrive at the “proof of
    the fact” that the Earth was either moving or at rest. This was contrary to Ptolemy’s
    position in the Almagest (I.7), namely that one could establish a static Earth through
    observation. After Tusi, we can trace a three-century discussion in which various
    authors argued whether he or Ptolemy was correct regarding the possibility of an
    observational proof of the Earth’s state of rest. Qushji, though, took a somewhat
    different approach. Starting with his view that the astronomer should not depend on
    the natural philosopher, but also rejecting Ptolemy’s view that an observational test
    was possible, Qushji made the remarkable claim that nothing false follows from the
    assumption of a rotating Earth.41

    The connection with Copernicus, though, might seem tenuous at best. What makes
    this an arguable possibility is the remarkable coincidence between a passage in De
    revolutionibus (I.8) and one in Tusi’s Tadhkira (II.1[6]) in which Copernicus follows
    Tusi’s objection to Ptolemy’s “proofs” of the Earth’s immobility.42 This passage,
    which is quoted by numerous Islamic scholars after Tusi, including Qushji, formed
    the starting point for their discussion of the Earth’s possible motion. The closeness
    of the passage in Copernicus is one more bit of evidence that he seems to have been
    influenced not only by Islamic astronomical models but also by a conceptual revolution
    that was going on in Islamic astronomy. This conceptual revolution was opening
    up the possibility for an alternative “astronomical” physics that was independent of
    Aristotelian physics.

    It is this point that has been missed up to now in seeking to understand the Islamic
    background to Copernicus. Clearly there is more to the Copernican revolution than
    some clever astronomical models that arose in the context of a criticism of Ptolemy.
    There also needed to be a new conceptualization of astronomy that could allow for an
    astronomically-based physics. But there is hardly anything like this in the European
    tradition before Copernicus.43 The fact that we can find a long, vigorous discussion
    in Islam of this issue intricately-tied to the question of the Earth’s movement should
    indicate that such a conceptual foundation was there for the borrowing. It will be
    argued, of course, that the mechanism for such borrowing has yet to be found. But
    again, in my opinion it is more important at this point in our knowledge to focus on
    the products rather than the mechanism of transmission. By doing so, we can get a
    clearer idea not only of the possible Islamic connection to Copernicus but also of
    the Copernican revolution itself.


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