Pre-Islamic Arabs The Islamic historian
Ahmad Dallal notes that, unlike the
Babylonians,
Greeks, and
Indians, who had developed elaborate systems of mathematical
astronomical study, the
pre-Islamic Arabs relied upon
empirical observations. These were based on the rising and setting of particular stars, and this indigenous
constellation tradition was known as '
. The study of ' was developed after
Islamization when Arab astronomers introduced mathematics to their study of the night sky.
Early period The first astronomical texts that were translated into
Arabic were of Indian and Persian origin. The most notable was
Zij al-Sindhind, a
zij produced by
Muḥammad ibn Ibrāhīm al-Fazārī and
Yaʿqūb ibn Ṭāriq, who translated an 8th-century Indian astronomical work after 770, with the assistance of Indian astronomers who were at the court of caliph
Al-Mansur. '''' was also based upon Indian
astronomical tables, compiled in the
Sasanian Empire over a period of two centuries. Fragments of texts during this period show that Arab astronomers adopted the
sine function from India in place of the
chords of
arc used in
Greek trigonometry. Ptolemy's Almagest (a geocentric spherical Earth cosmic model) was translated at least five times in the late eighth and ninth centuries, which was the main authoritative work that informed the Arabic astronomical tradition. The rise of
Islam, with its obligation to determine the five daily
prayer times and the
qibla (the direction towards the
Kaaba in the
Sacred Mosque in
Mecca) inspired intellectual progress in astronomy.
Astronomical methods The
philosopher Al-Farabi (d. 950) described astronomy in terms of mathematics, music, and optics. He showed how astronomy could be used to describe the Earth's motion, and the position and movement of celestial bodies, and separated mathematical astronomy from science, restricting astronomy to describing the position, shape, and size of distant objects. Al-Farabi used the writings of
Ptolemy, as described in his
Analemma, a way of calculating the Sun's position from any fixed location.
Golden Age is a mathematical device invented by
Nasir al-Din al-Tusi in which a small
circle rotates inside a larger circle twice the
diameter of the smaller
circle. Rotations of the circles cause a point on the
circumference of the smaller circle to
oscillate back and forth in
linear motion along a diameter of the larger circle.
The House of Wisdom was an academy that was open to the public and financially supported during the reign of the Abbasid caliph
al-Ma'mun in the early 9th century in Baghdad. Astronomical research was greatly supported by al-Mamun through the House of Wisdom, al-Ma'mun also built the first observatory in Baghdad and subsequent observatories were built around regions of
Iraq and
Iran. The first major Muslim work of astronomy was
Zij al-Sindhind, produced by the mathematician
Muhammad ibn Musa al-Khwarizmi in 830. It contained tables for the movements of the Sun, the Moon, and the planets
Mercury,
Venus,
Mars,
Jupiter and
Saturn. The work introduced Ptolemaic concepts into Islamic science, and marked a turning point in Islamic astronomy, which had previously concentrated on translating works, but which now began to develop new ideas. Another notable figure in al-Ma'mun's court was
Sind ibn 'Alī, a Jewish convert to Islam, who contributed to the
Zīj al-Sindhind and was credited with constructing astronomical instruments. Jewish scholars in the Islamic world also engaged with astronomical methods developed by their Muslim counterparts. In 931,
Saadia Gaon (a leading rabbi and head of the
Sura Academy in Iraq) used a
zīj to calculate the positions of the sun, moon, and five visible planets at a specific time, as noted in his commentary on
Sefer Yetzirah. He may have studied the
zīj tradition in part to counter contemporaries who sought to use such calculations to determine and sanctify the new moon each month. 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 's astronomical works that explains the different
phases of the moon, with respect to the position of the
Sun.
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. 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 [or 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
Najm al-Din al-Qazwini al-Katibi (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.
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,
Ibn Tufail, and
Ibn Rushd. A notable example is
Nur ad-Din al-Bitruji, who considered the Ptolemaic model mathematical, and not physical. Al-Bitruji proposed a theory on
planetary motion in which he wished to avoid both
epicycles and eccentrics. He was unsuccessful in replacing Ptolemy's planetary model, as the numerical predictions of the planetary positions in his configuration were less accurate than those of the Ptolemaic model. One original aspects of al-Bitruji's system is his proposal of a physical cause of celestial motions. He contradicts the Aristotelian idea that there is a specific kind of dynamics for each world, applying instead the same dynamics to the sublunar and the celestial worlds.
Later period In the late 13th century, Nasir al-Din al-Tusi created the Tusi couple, as pictured above. Other notable astronomers from the later medieval period include
Mu'ayyad al-Din al-Urdi (),
Qutb al-Din al-Shirazi (),
Sadr al-Sharia al-Bukhari (),
Ibn al-Shatir (), and
Ali Qushji (). In the 15th century, the
Timurid ruler
Ulugh Beg of
Samarkand established his court as a center of patronage for astronomy. He studied it in his youth, and in 1420 ordered the construction of Ulugh Beg Observatory, which produced a new set of astronomical tables, as well as contributing to other scientific and mathematical advances. Several major astronomical works were produced in the early 16th century, including ones by
Al-Birjandi (d. 1525 or 1526) and Shams al-Din al-Khafri (fl. 1525). However, the vast majority of works written in this and later periods in the history of Islamic sciences are yet to be studied. ==Influences==