Before Islam emerged in the Middle East, astronomy was developing within individual civilisations and declining with the decline of those civilisations. Occasionally, knowledge would pass from one civilisation to another, but with the Arab caliphates came something unique, something that would propel Islamic astronomy into heights not seen by any other civilisation before.
Pre-Islamic Arabs relied on stars for navigation when travelling through deserts on Arab peninsula, because they had no reference points they could use for orientation. With Islam and Arab conquest of the Middle East, a new need emerged. Muslims always pray facing Mecca and at certain times during the day. At the very beginning, in their own lands, this was not an issue, since they always knew in which direction Mecca was. But as they conquered vast lands, their caliphate ended up covering 15 million square kilometres and without some way to determine the direction which to face, they wouldn’t have been able to pray in accordance with their laws. It shouldn’t come as a surprise then, that astronomy played an important role in Islamic world. Not just for determining where Mecca was, but also for timekeeping and knowing when to pray. Their calendar, called Hijri calendar, is a lunar calendar where year is 254 days long and has 12 months. It is used to this day and is basis for setting the starting day of Ramadan.
As mentioned, Arabs were good at observing stars since pre-Islamic days, but as they conquered other lands and spread from India to Iberian peninsula, they had the chance to learn from Hellenistic, Persian and especially Indian astronomers and enter the golden age of their astronomy, science and society in general. Unlike the Greeks who were concerned with cosmology and underlying theories, Islamic astronomers relied more on observations and measurements. Especially is interesting the combination of Indian mathematics and Islamic astronomy, based on observations, which resulted in zijes, series of astronomical books that spanned for over 11 centuries.
In late 8th century, Arabs moved their capital to Baghdad which soon became an important centre, with Silk Road and other major roads going through it. In the city’s House of Wisdom, foreign texts were translated in order to move on from oral society to the one using written language. With the arrival of commerce and trade came scholars as well. All this contributed to advancement of Islamic astronomy, with Baghdad becoming a melting pot for scientific ideas from different cultures.
al-Sindh was the first major zij, written by al-Khwarizmi in 830. In it, movement of the Sun, the Moon and the five known planets are recorded and the Ptolemaic concepts were introduced to Islamic astronomy.
Islamic astronomers adopted the Ptolemaic geocentric system from the Hellenistic astronomers.
Thanks to them, one of the most influential scientific books of all times, Ptolemy’s Almagest, was translated into Arabic and kept relevant, while in the medieval Europe it was forgotten during what we now call the Dark Ages. Almagest is a primary source of information on Greek astronomy we have today. Islamic astronomers criticised the book, upgraded the Ptolemaic system, changed some aspects of it and made new models, but they never transitioned to the heliocentric system during this time period.
This criticism of Ptolemy's Almagest began in 1028 with Ibn al-Haytham’s “Doubts of Ptolemy” after which many Islamic astronomers began developing alternate models to correct Ptolemaic system’s shortcomings.
Before the decline of the Caliphate and the end of the Islamic Golden Age, Islamic astronomy influenced other civilisations and set basis for many discoveries during the Renaissance in Europe. When Genghis Khan and his Mongols sacked Baghdad and brought the Caliphate to their knees, he also adopted some of their knowledge by bringing Islamic astronomers to China to work on improving Chinese calendar and astronomy in general. Islamic calendar even served as a basis for Korean calendar reform.
Widely used instrument in Islamic astronomy was astrolabe. Invented by the Greeks, it was perfected by Islamic astronomers and used mainly for finding the direction of Mecca, determining the beginning of Ramadan and the hours at which to pray. Sundials were also used to set the time for prayer. They too were adopted from the Greeks and the Indians, but improved by Arabs. Two instruments that were actually invented by Islamic astronomers were quadrant, an improved version of astrolabe, and equatorium, used for determining position of the Sun, the Moon and planets without calculations. On larger scale, Muslims built observatories, largest of which were in Isfahan (in modern-day Iran), Samarkand (Uzbekistan), Istanbul (Turkey), and most notably Maragha (Iran), where the most influential observatory was built by Hulagu Khan.
As Europe began to recover from the Dark Ages, their science began to progress once again and with it, of course, astronomy. Although Islamic astronomy declined with the end of Islamic Golden Age, their highly sophisticated instruments, together with some of almost 10,000 manuscripts Islamic astronomy produced, made their way into Europe. During the Renaissance, they had profound effect on development of astronomy in Europe that would lead to many important discoveries, including that of Galileo and Kepler. In the East, collaboration between Indian and Islamic astronomers left legacy in India that was built upon by Europeans they colonised India in the 17th century.
Compared to civilisations that came before them, Arabs had the first significant impact on astronomy we know today. Their effort to translate and preserve older manuscripts and produce many of their own, together with refinement of many instruments, was crucial for European astronomy, since most of what the ancient Greeks knew, Europeans had forgotten while India and China were on the other side of the world. It is not too far-fetched to claim that without Islamic astronomy and science in general, a lot of time would have been wasted on rediscovering what was known for thousands of years and forgotten.
Next time in Cosmic Quest, you will have the chance to find out more about Copernicus, Galileo, Kepler and Brahe and their discoveries that took place in Europe during the Renaissance.