Muslim astronomy

Islamic astronomy comprises the astronomical developments made in the Islamic world, particularly during the Islamic Golden Age (9th–13th centuries), and mostly written in the Arabic language. These developments mostly took place in the Middle East, Central Asia, Al-Andalus, and North Africa, and later in the Far East and India. It closely parallels the genesis of other Islamic sciences in its assimilation of foreign material and the amalgamation of the disparate elements of that material to create a science with Islamic characteristics. These included Greek, Sassanid, and Indian works in particular, which were translated and built upon.

Islamic astronomy played a significant role in the revival of Byzantine and EuropeanSaliba (1999). astronomy following the loss of knowledge during the early medieval period, notably with the production of Latin translations of Arabic works during the 12th century.
Islamic astronomy also had an influence on Chinese astronomy and Malian astronomy.

A significant number of stars in the sky, such as Aldebaran, Altair and Deneb, and astronomical terms such as alidade, azimuth, and nadir, are still referred to by their Arabic names. A large corpus of literature from Islamic astronomy remains today, numbering approximately 10,000 manuscripts scattered throughout the world, many of which have not been read or catalogued. Even so, a reasonably accurate picture of Islamic activity in the field of astronomy can be reconstructed.

History

Pre-Islamic Arabs

Ahmad Dallal notes that, unlike the Babylonians, Greeks, and Indians, who had developed elaborate systems of mathematical astronomical study, the pre-Islamic Arabs relied entirely on empirical observations. These observations were based on the rising and setting of particular stars, and this indigenous constellation tradition was known as ''Anwā’''. The study of ''Anwā’'' continued to be developed after Islamization by the Arabs, where Islamic astronomers added mathematical methods to their empirical observations.Dallal (1999), pg. 162

Early Abbasid era

The first astronomical texts that were translated into Arabic were of Indian and Persian origin. The most notable of the texts was ''Zij al-Sindhind'', an 8th-century Indian astronomical work that was translated by Muhammad ibn Ibrahim al-Fazari and Yaqub ibn Tariq after 770 CE with the assistance of Indian astronomers who visited the court of caliph Al-Mansur in 770. Another text translated was the ''Zij al-Shah'', a collection of astronomical tables (based on Indian parameters) compiled in Sasanid Persia over two centuries.
Fragments of texts during this period indicate that Arabs adopted the sine function (inherited from India) in place of the chords of arc used in Greek trigonometry.

According to David King, after the rise of Islam, the religious obligation to determine the qibla and prayer times inspired progress in astronomy. Early Islam's history shows evidence of a productive relationship between faith and science. Specifically, Islamic scientists took an early interest in astronomy, as the concept of keeping time accurately was important for the five daily prayers central to the faith. Early Islamicate scientists constructed astronomical tables specifically to determine the exact times of prayer for specific locations around the continent, serving effectively as an early system of time zones.

Astronomical methods

Al-Farabi (d. 950) was a philosopher who had a method of knowing what astronomy was. He describes mathematical astronomy but also can convey a sense of understanding of astronomy presented with music/optics. In a mathematical sense, astronomy can be broken up into three parts as explained by Al-Farabi. He shows that inhabited and uninhabited places on earth can be examined with astronomy how the earth moves and from day or night. Another is the movement of different Astronomical objects of where they move to, number of motions, and where they started. The third one is the shapes/sizes/positioning of the celestial bodies to obtain. Al-Farabi's believes that his idea of mathematical astronomy is separate from science. Such as physics dealing with the internal aspect of planets, what they can be made out of. Astronomy is restricted to the external aspect, such as positioning, shape, and size. This helps show how Al-Farabi's method of figuring out knowledge on what astronomy was can not correct. Namely to separate physics and astronomy as two separate sciences in order to discover more about the subject.

Al-Farabi had followed some of the same ideas as Ptolemy. This was because Ptolemy enjoyed observations and only knew mathematics to be an accurate way of composing compelling reason. Rather than having to deal with physics and metaphysics because they were seen as unreliable to help prove theories of the universe. Ptolemy had a mathematical way of astronomy just as Al-Farabi. His way was called Analemma, which is a way to calculate the Suns position from a fixed location. Within old historic texts, such as Vitruvius Architecture IX.7, and Hero of Alexandria's Dioptra 35, analemma's were drawn to help solve answers to problems that had to deal with geometry, possibly about astronomy. The analemma was shown to be one of Ptolemy's Hypothesis' for problem-solving. An analemma is very complicated and difficult to understand with multiple techniques on how to draw and perform the math of one. It was very common for many people to group the sundial and analemma together. Ptolemy's analemma helped the Islamic period thrive because it was used continuously to locate the sun.

Golden Age

The House of Wisdom was an academy established in Baghdad under Abbasid caliph Al-Ma'mun in the early 9th century. Astronomical research was greatly supported by the Abbasid caliph al-Mamun through the House of Wisdom. Baghdad and Damascus became the centers of such activity.

The first major Muslim work of astronomy was ''Zij al-Sindhind'' by mathematician al-Khwarizmi in 830. The work contains tables for the movements of the Sun, the Moon, and the five planets known at the time. The work is significant as it introduced Ptolemaic concepts into Islamic sciences. This work also marks the turning point in Islamic astronomy. Hitherto, Muslim astronomers had adopted a primary research approach to the field, translating works of others and learning already discovered knowledge. Al-Khwarizmi's work marked the beginning of nontraditional methods of study and calculations.

Doubts on Ptolemy

In 850, al-Farghani wrote ''Kitab fi Jawami'' (meaning "A compendium of the science of stars"). The book primarily gave a summary of Ptolemic cosmography. However, it also corrected Ptolemy based on the findings of earlier Arab astronomers. Al-Farghani gave revised values for the obliquity of the ecliptic, the precessional movement of the apogees of the Sun and the Moon, and the circumference of the Earth. The book was widely circulated through the Muslim world, and translated into Latin.

By the 10th century texts appeared regularly whose subject matter was doubts concerning Ptolemy (''shukūk''). Several Muslim scholars questioned the Earth's apparent immobility and centrality within the universe. From this time, independent investigation into the Ptolemaic system became possible. According to Dallal (2010), the use of parameters, sources and calculation methods from different scientific traditions made the Ptolemaic tradition "receptive right from the beginning to the possibility of observational refinement and mathematical restructuring".

Egyptian astronomer Ibn Yunus found fault in Ptolemy's calculations about the planet's movements and their peculiarity in the late 10th century. Ptolemy calculated that Earth's wobble, otherwise known as precession, varied 1 degree every 100 years. Ibn Yunus contradicted this finding by calculating that it was instead 1 degree every 70 years.

Between 1025 and 1028, Ibn al-Haytham wrote his ''Al-Shukuk ala Batlamyus'' (meaning "Doubts on Ptolemy"). While maintaining the physical reality of the geocentric model, he criticized elements of the Ptolemic models. Many astronomers took up the challenge posed in this work, namely to develop alternate models that resolved these difficulties. In 1070, Abu Ubayd al-Juzjani published the ''Tarik al-Aflak'' where he discussed the "equant" problem of the Ptolemic model and proposed a solution. In Al-Andalus, the anonymous work ''al-Istidrak ala Batlamyus'' (meaning "Recapitulation regarding Ptolemy"), included a list of objections to Ptolemic astronomy.

Nasir al-Din al-Tusi, the creator of the Tusi couple, also worked heavily to expose the problems present in Ptolemy's work. In 1261, Tusi published his Tadkhira, which contained 16 fundamental problems he found with Ptolemaic astronomy, and by doing this, set off a chain of Islamic scholars that would attempt to solve these problems. Scholars such as Qutb al-Din al-Shirazi, Ibn al-Shatir, and Shams al-Din al-Khafri all worked to produce new models for solving Tusi's 16 Problems, and the models they worked to create would become widely adopted by astronomers for use in their own works.

Nasir al-Din Tusi wanted to use the concept of Tusi couple to replace the "equant" concept in Ptolemic model. Since the equant concept would result in the moon distance to change dramatically through each month, at least by the factor of two if the math is done. But with the Tusi couple, the moon would just rotate around Earth resulting in the correct observation and applied concept. Mu'ayyad al-Din al-Urdi was another engineer/scholar that tried to make sense of the motion of planets. He came up with the concept of lemma, which is a way of representing the epicyclical motion of planets without using Ptolemic method. Lemma was intended to replace the concept of equant as well.

Earth rotation

Abu Rayhan Biruni (b. 973) discussed the possibility of whether the Earth rotated about its own axis and around the Sun, but in his ''Masudic Canon'', he set forth the principles that the Earth is at the center of the universe and that it has no motion of its own. He was aware that if the Earth rotated on its axis, this would be consistent with his astronomical parameters, but he considered this a problem of natural philosophy rather than mathematics.

His contemporary, Abu Sa'id al-Sijzi, accepted that the Earth rotates around its axis. Al-Biruni described an astrolabe invented by Sijzi based on the idea that the earth rotates:

The fact that some people did believe that the earth is moving on its own axis is further confirmed by an Arabic reference work from the 13th century which states:

According to the geometers r engineers(''muhandisīn''), the earth is in a constant circular motion, and what appears to be the motion of the heavens is actually due to the motion of the earth and not the stars.

At the Maragha and Samarkand observatories, the Earth's rotation was discussed by al-Kātibī (d. 1277), Tusi (b. 1201) and Qushji (b. 1403). The arguments and evidence used by Tusi and Qushji resemble those used by Copernicus to support the Earth's motion. However, it remains a fact that the Maragha school never made the big leap to heliocentrism.Toby E.Huff(1993):''The rise of early modern science: Islam, China, and the West

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Alternative geocentric systems

In the 12th century, non-heliocentric alternatives to the Ptolemaic system were developed by some Islamic astronomers in al-Andalus, following a tradition established by Ibn Bajjah