@article{2017,title={OMAR KHAYYAM AND STUDIES ASTRONOMY AT THE OBSERVATORY IN ISFAHAN},abstractNode={Omar Khayyam made significant studies about Astronomy during the Great Seljuks era. During the Sultan Melikşah era he was the head of the committee that got together to form a new calender in İsfahan Observatory. As a director of that observatory he became the initiator of the studies and observations and considering the results he generated the Celali Calender. Celali Calender that was formed by the science team of İsfahan observatory gave more sensitive and punctual results compared to Miladi Calender. This event is an important one that shows the level we came in Astronomy during the Great Seljuks era.},author={Seyfettin Kaya},year={2017},journal={Cappadocia Journal of History and Social Sciences}}