History of Astronomy - Islamic Astronomy

Islamic Astronomy

The Arabic world under Islam had become highly cultured, and many important works of knowledge from Greek astronomy and Indian astronomy were translated into Arabic, used and stored in libraries throughout the area. An important contribution by Islamic astronomers was their emphasis on observational astronomy This led to the emergence of the first astronomical observatories in the Muslim world by the early 9th century. Zij star catalogues were produced at these observatories.

The late 9th century Persian astronomer Ahmad ibn Muhammad ibn Kathīr al-Farghānī wrote extensively on the motion of celestial bodies. His work was translated into Latin during the Latin translations of the 12th century. In the 9th century, Ja'far ibn Muhammad Abu Ma'shar al-Balkhi (Albumasar) developed a planetary model which has been interpreted as a heliocentric model. This is due to his orbital revolutions of the planets being given as heliocentric revolutions rather than geocentric revolutions, and the only known planetary theory in which this occurs is in the heliocentric theory. His work on planetary theory has not survived, but his astronomical data was later recorded by al-Hashimi and Biruni.

In the 10th century, Abd al-Rahman al-Sufi (Azophi) carried out observations on the stars and described their positions, magnitudes, brightness, and colour and drawings for each constellation in his Book of Fixed Stars. He also gave the first descriptions and pictures of "A Little Cloud" now known as the Andromeda Galaxy. He mentions it as lying before the mouth of a Big Fish, an Arabic constellation. This "cloud" was apparently commonly known to the Isfahan astronomers, very probably before 905 AD. The first recorded mention of the Large Magellanic Cloud was also given by al-Sufi. In 1006, Ali ibn Ridwan observed SN 1006, the brightest supernova in recorded history, and left a detailed description of the temporary star.

In the late 10th century, a huge observatory was built near Tehran, Iran, by the astronomer Abu-Mahmud al-Khujandi who observed a series of meridian transits of the Sun, which allowed him to calculate the obliquity of the ecliptic, also known as the tilt of the Earth's axis relative to the Sun. In 11th-century Persia, Omar Khayyám compiled many tables and performed a reformation of the calendar that was more accurate than the Julian and came close to the Gregorian.

In the early 11th century, Ibn al-Haytham (Alhazen) wrote the Maqala fi daw al-qamar (On the Light of the Moon) some time before 1021. This was the earliest attempt at applying the experimental method to astronomy and astrophysics, and thus the first successful at combining mathematical astronomy with "physics" (which then referred to natural philosophy) for several of his astronomical hypotheses. He disproved the universally held opinion that the moon reflects sunlight like a mirror and correctly concluded that it "emits light from those portions of its surface which the sun's light strikes." In order to prove that "light is emitted from every point of the moon's illuminated surface," he built an "ingenious experimental device." Ibn al-Haytham had "formulated a clear conception of the relationship between an ideal mathematical model and the complex of observable phenomena; in particular, he was the first to make a systematic use of the method of varying the experimental conditions in a constant and uniform manner, in an experiment showing that the intensity of the light-spot formed by the projection of the moonlight through two small apertures onto a screen diminishes constantly as one of the apertures is gradually blocked up."

Other Muslim advances in astronomy included the collection and correction of previous astronomical data, resolving significant problems in the Ptolemaic model, the development of the universal latitude-independent astrolabe by Arzachel, the invention of numerous other astronomical instruments, the beginning of astrophysics and celestial mechanics after Ja'far Muhammad ibn Mūsā ibn Shākir theorized that the heavenly bodies and celestial spheres were subject to the same physical laws as Earth, the first elaborate experiments related to astronomical phenomena, the introduction of exacting empirical observations and experimental techniques, and the introduction of empirical testing by Ibn al-Shatir, who produced the first model of lunar motion which matched physical observations.

In the 12th century, Fakhr al-Din al-Razi criticized the idea of the Earth's centrality within the universe, and instead argued that there are more than "a thousand thousand worlds (alfa alfi 'awalim) beyond this world such that each one of those worlds be bigger and more massive than this world as well as having the like of what this world has." The first empirical observational evidence of the Earth's rotation was given by Nasīr al-Dīn al-Tūsī in the 13th century and by Ali Qushji in the 15th century, followed by Al-Birjandi who developed an early hypothesis on "circular inertia" by the early 16th century. Natural philosophy (particularly Aristotelian physics) was separated from astronomy by Ibn al-Haytham (Alhazen) in the 11th century, by Ibn al-Shatir in the 14th century, and Qushji in the 15th century, leading to the development of an independent astronomical physics.

It is known that the Copernican heliocentric model in Nicolaus Copernicus' De revolutionibus employed geometrical constructions that had been developed previously by the Maragheh school, and that his arguments for the Earth's rotation were similar to those of Nasīr al-Dīn al-Tūsī and Ali al-Qushji. Some have referred to the achievements of the Maragha school as a "Maragha Revolution", "Maragha School Revolution", or "Scientific Revolution before the Renaissance".