Persia, which, after the downfall of the Abbasid Caliphate formed the nerve centre of Islamic learning, produced some of the greatest intellectuals of mediaeval times. Great advances were made in almost all branches of knowledge. One of the most outstanding intellectuals of Islam was Abu Rehan Beruni (973--1048 A.D.) who graced the literary meetings of Mahmud Ghaznaui. "Few know physics and metaphysics" says J. N. Sircar, the celebrated Indian historian, "amongst those few the greatest in Asia was Al-Beruni, at once a philosopher and a scientist and preeminent in both of these two seemingly incompatible fields".' Al-Beruni was a distinguished and original scholar of astronomy and other sciences. His Al-Qanun al-Masudi written for his patron Sultan Masud of Ghazni in 1030 A.D. is an astronomical encyclopaedia. A short catechism of geometry, arithmetic, astronomy and astrology also written in 1030 A.D. and entitled Al-Tahfin li-awail sinaat al-l\rajum deals chiefly with the calenders and eras of ancient peoples. The rotation of the earth on its axis and the accurate determination of longitudes and latitudes were also elaborately discussed in this book.

Malik Shah Saljuqi and his illustrious grand vazir Nizamul Mulk Toosi were also great patrons of learning during those times. They established an observatory at Rayy or Neshapur in 1074-75 A.D. where under the guidance of Omar Khayyam and Abdur Rahman al-Hazini astronomical observations were made. Their research led to a reformed calendar which preceded the Cregorian calender by 600years. According to Sedillot, who is an authority on the subject, "it is more exact". This calendar formulated by Omar Khayyam was named Al-Tarikh Jalali after his patron Jalaluddin Malik Shah Seljuqi, and is based on an accurate determination of the length of the tropical year. The Gregorian calendar leads to an error of one day in 3,330 years whereas Khayyam's apparently leads to an error of one day in about 5,000 years.

The destruction wrought by the Mongol hordes served a death blow to all cultural and intellectual movements in the world of Islam. The cultural treasures amassed during centuires of intellectual pursuits was reduced to ashes. On the downfall of the Abbasid Caliphate there sprang up small Muslim principalities who kept aloft the candle of learning and vied with each other in the patronage of scholars and scientists. A year after the fall of Baghdad, in 1259 A.D., Hulagu Khan started the construction of the Khaniz observatory in Maragah (Turkistan). This was the best observatory of its time, working under the directorship of the celebrated genius and astronomer of that era, Nasiruddin Toosi, and equipped with the best available instruments including an armillary sphere, the mural quadrant and a solstitial armil. The remains of this observatory are still extant and it was here that Toosi compiled his famous astronomical tables known as al zij' al il khani which earned much popularity throughout Asia including China. Nasiruddin Toosi also wrote Tazkirah fi'ilm al-Hai'a', an outstanding work on astronomy.

Samarqand, the capital of the famous conqueror Tamerlane became in those days a great centre of Islamic education. An astronomical table prepared in 1437 for a prince of the family of Tamerlane and called Table of Ulugh Beg was much appreciated in Europe and according to Carra De Vaux was published in England in the 18th century A.D.

The Arab civilization of Spain rivalled that of the Abbasid's in the East, and during the middle of the IOth century astronomical studies were especially favoured by the rulers of Muslim Spain. The outstanding Spanish astronomers were Al-Majriti of Cordova, al-Zarqali (1029--1087 A.D.) of Toledo, Ibn Afiah (d/2140-50 A.D.) of Seville and Nur-ud-din Abu Ishaq al-Bitruji.

In his famous work Kitab al Hayat (book of astronomy), which was later translated into Latin by Gerard of Cremona, Jabir Ibn Afiah, the celebrated astronomer of the twelfth century, sharply criticised Ptolemy. Against the observations of Ptolemy he rightly observed that the lower planets, Mercury and Venus, have no visible parallaxes. His generalisations of the subject were confirmed by later research.

Al-Zarqali (Arzachel 1029-1087 A.D.) was the foremost astronomical observer of Muslim Spain. He was the celebrated instrument maker who constructed an improved type of astrolabe (a saJilza) on which he wrote a treatise. His calculations of the length of the Mediterranean Sea as 42 degrees was approximately accurate in comparison to Ptolemy's estimate of 62" and Al-Khwarizmi's estimate of 52". He also has the distinction of being the first astronomer to prove the motion of the solar apogee with reference to stars. His works along with those of Al-Battani were studied and.appreciated in the West and Copernicus quotes him in his well known work De Revolutionibus Orbizrm Coelestium.

Nur-ud-Din Abu Ishaq al-Bitruji (Alpetragius), was foremost among the last astronomers of Spain, whose outstanding work Kitab al-Hai'a was translated into Latin by Michael Scot in 1217 and into Hebrew in 1259 A.D. He is considered the exponent of a new astronomy and his book marks the culmination of the anti-Ptolemaic movement. According to Draper, "increased accuracy was given to the correction of the astronomical observations by Alhazen's great discovery of atmospheric refraction."

"Finally it was through Spanish channels" says Philip K. Hitti, "that the Latin West found its oriental inspiration in astronomy and astrology. The leading Muslim astronomical works were translated in Spain into Latin, and the Alfonsine tables compiled under the aegis of Alfonso X in the 13th century were but a development of Arab astronomy".l According to R..Briffault, "Arab astronomy did not forestall Copernicus or Newton, though without it there would have been no Copernicus and Newton" 2.

The Muslims, have thus made the greatest contributions to astronomical knowledge during mediaeval times.