Friday, September 21, 2012

The Arabic and Islamic sstronomy

Studying the universeDuring the period when the Western civilization was experiencing the Middle Ages, between 700 and 1200 A.D., an Islamic empire was stretching from Central Asia to southern Europe. In this area, people were appreciating very much the education and they greatly contributed to the science and mathematics domains. Many classical Greek and Roman works were translated into Arabic and scientists expanded those ideas.

For example, the geocentric model of Ptolemy formed the basis of the Arab and Islamic astronomy, but several Islamic astronomers have made certain observations and calculations which were much more accurate than the ones of Ptolemy. Perhaps the most fascinating aspect of the Islamic astronomy is the fact that it was built on the sciences of two great cultures (Greek and Indian). Blending and expanding these different ideas led to a new science which later influenced the Western scientific exploration, starting with the Renaissance.

Perhaps the most vital reason for which the Muslims studied the sky in so much detail was for the purpose of time-measuring. The Islamic religion asks the believers to pray five times a day, when the Sun is situated in specific positions. Measuring the time with the help of astronomy was the most accurate way to determine the moments when the Muslims had to pray; it was also used to establish the date of the religious festivals.

The Muslim holy book, the Koran, makes frequent reference to the astronomical patterns that are visible in the sky and is a major source of the traditions associated with the Islamic astronomy. Another important use of the astronomy for religious purpose was for the determination of latitude and longitude. Using the stars as guides, especially the Polar Star, several tables were compiled, which calculated the latitude and longitude of important cities in the Islamic world. Using this information, the Muslims could be assured that they were praying in the direction of Mecca, as it is specified in the Koran.

Arabic astronomy

Besides its use for religious purposes, astronomy was also used as a tool for navigation. The astrolabe (an instrument which calculated the positions of certain stars in order to determine the direction) was invented by the Greeks and adopted and perfected by the Arabs. The sextant was developed by the Arabs, this being a more sophisticated version of the astrolabe. This instrument ultimately became the cornerstone in the navigation domain for the European explorers.

In the Islamic world, science was considered the highest purpose and it was strongly supported by the nobility. Most scientists were working in the courts of regional leaders and were financially rewarded for their achievements. In 830, the Khalifah Al-Mamuun founded Bayt-al-Hikman (the House of Wisdom), as a gathering place where the researchers could translate texts from Greek and Persian into Arabic. These texts have formed the basis of the Islamic scientific knowledge.

One of the greatest Islamic astronomers was Al-Khwarizmi, who lived in the 9th century and was the inventor of algebra. He developed this mathematical device completely in words and not in mathematical expressions, but he based the system on the Indian numbers borrowed by the Arabs (what we today call them Arabic numerals). After several hundreds of years, his work was translated into Latin and served as the introduction of the Indian number system in Europe, together with zero. Al-Khwarizmi performed detailed calculations of the positions of the Sun, Moon, and planets, and also did calculations of the eclipses. He constructed a table of the latitudes and longitudes of 2402 cities and landmarks, forming the basis of an early world map.

Another Islamic astronomer who had an impact on the Western science was Al-Farghani. In the late 9th century, he wrote very much about the motion of the celestial bodies. Like many other Islamic astronomers, Al-Farghani accepted the geocentric model of Ptolemy, not only in the Islamic world but also throughout the entire Europe. In the 12th century, his works were translated into Latin, and it is said that Dante got his astronomical knowledge from the books of Al-Farghani.

In the late 10th century, the astronomer Al-Khujandi has built a huge observatoryAstronomy near Tehran, in Iran. He built a large sextant inside the observatory and was the first astronomer who was capable of measuring with an accuracy of arc seconds. He observed a series of transits types of the Sun, which allowed him to calculate the tilt of Earth?s axis in relation to the Sun. As we know today, Earth?s tilt is approximately 23?34?, and al-Khujandi measured it as being 23?32?19?. Using this information, Al-Khujandi also compiled a list of latitudes and longitudes of the major cities.

Omar Khayyam was a great Persian scientist, philosopher and poet who lived between 1048 and 1131. He compiled several astronomical tables and performed a reformation of the calendar, which was much more accurate than the Julian calendar and close to the Gregorian one. An amazing thing was his calculation regarding the length of the year (365.24219858156), which is accurate to the 6th decimal! Western science owes very much to the Islamic and Arab scientists, whose contributions range from the Arabic names of the stars that we still use today, to the mathematical and astronomical treaties used by Europeans to enter the modern world of science.

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