NASIR AL-DIN AL-TUSI

In 2001 it is 800 years since birthday of Abu Jafar Muhammad Ibn Muhammad Ibn al-Hasan Nasir al-Din al-Tusi, which is a great scientist of the medieval east. By decision of UNESCO this anniversary has been marked at international level. The more detailed information on this subject can be obtained on the publications of the Shamakhy Astrophysical Observatory.

After having assimilated in VII-X centuries the cultures of many peoples of the Arab caliphate has formed a new stake of global culture - culture of the arab or moslem medieval east. The accepted term for the blossom period of this culture is Moslem Rennessaince. After mongols defeated the caliphate in XII century the science and the culture kept developing in territory of the Central Asian states, Iraq, Iran (in southern Azerbaijan) and Afghanistan. Milestones of development of astronomy within the framework of this culture are:

1.Translations of the scientific works from the ancient indian and greek languages into arabian and creation of an observatory at " the House of wisdom " - Baghdad academy of sciences. Particularly, it?s worth to note complete translation famous " Megale of sintaksis? of Ptolemeus. As well as al-Battani?s clarification of the value of declination of ecliptic to equator and discovery by him of a motion of apogee of the Sun, Abul- Vefa?s finding of a new inequality in the motion of the moon ? variations of the moon. Of works dated after the X century - observatory and " the House of knowledge " in Cairo, where Ibn Yunis (950-1009) worked.

2. The works of the great Central Asian scientist and thinker Biruni (973-1048) include the measurement with high precision of declination of ecliptic to equator - 23°34'00 " and determination of diminution of this quantity over 100 years - 52'6". The invention of the method similar to triangulations discovered later in 1617 by Snellius. Observatory in Isfahan, where the scientist and poet Omar Hayam (about 1048 ? after 1122) worked.

3. XIII - XV centuries - activities of the two largest scientific schools of the medieval east : Maraga school headed by al-Tusi and Samarkand school of Ulugbek.

The new stage of development of astronomy following the ancient greek and the ancient indian astronomies was stipulated by creation of its mathematical apparatus - trigonometric methods and trigonometry as an independent science. Increase of sizes of astronomical tools - index glasses and quadrants, the transition to lengthy systematic observations revealed inexactness of Ptolemeus table and boosted the development. The said in high degree refers to Maraga and Samarkand scientific schools.

Nasir-al-Din al-Tusi (1201 -1274), a native of Hamadan, which is on territory of Southern Azerbaijan, organized near Tabriz, in Maraga the biggest for that time observatory. He clarified the constant value of precession, having obtained for it the value of 51",4 per year. Under his supervision ?Ilhan tables" were composed. These tables consist of the new star catalogue, the table of the Sun, moon and planets.

Al-Tusi reach highest popularity after his development of Ptolemeu's model of motions of the moon and the planets. Ptolemeu's model featuring motions of celestial bodies within the framework of the geocentric conception was grounded on the principle of epicyclic motion. The motion of each planet was modelled with the help of the entire system of deferents and epicycles. In order to get the model better agree with observations, relative sizes and declinations of epicycles to ecliptic and to own deferents and were selected.

Despite all deficiencies this model remained unsurpassed during 1500 years. This is because it allowed with fairly good precision (compared to those times) to calculate the position of celestial objects for any date of time.
One of the main deficiencies of this system was departure from Aristotel. Aristotel believed that the motion of celestial objects must have been even and circular. The first model that met these conditions and gave good precision belongs to al-Tusi. With the help of the special lemma he achieved a rectilinear motion out of two even circular motions. In his lemma he proved that if a circle of diameter d rolled within another circle of diametr 2d, then the any point of a small circle will commit rectilinear movement along a diameter of the large circle.

A.Rustamov