Muslims had always had a special interest in astronomy. The moon and the sun are of vital importance in the daily life of every Muslim. By the moon, Muslims determine the beginning and the end of the lunar month. By the sun, Muslims calculate the times for prayer and fasting. It is also by means of astronomy that Muslims can determine the precise direction of the Qiblah.
Muslim astronomers were the first to establish observatories (buildings used for scientific observation of natural phenomena such as astronomical objects, the weather or earthquakes), like the one built at Mugharah by Hulagu, the son of Genghis Khan, in Persia, present day Iran. They also invented instruments such as the quadrant (device for measuring angle of the star) and astrolabe (an early instrument used to observe the position and determine the altitude of the sun and other astronomical objects), which led to advances not only in astronomy but in oceanic navigation, contributing to the European age of exploration.
Muslim philosophers and astronomers had inherited the Ptolemaic planetary system from the Greeks that hypothesized the principle of uniform circular motion allowing the planets to move in epicycles. However, Muslim astronomers eventually came to reject this theory in that the epicyclic movement violated the principle of uniformity of motion. In the 13th century, Al-Tusi, put forward his concept known as the “Tusi Couple,” a hypothetical model of “epicyclic motion that involves a combination of motions each of which was uniform with respect to its own center.” This model was applied by Ibn al-Shatir to the motions of the heavenly bodies in the fourteenth century.
Al-Battani determined the solar year of 365 days, 5 hours, 46 minutes, and 24 seconds. Thus Muslim scholars worked in all major branches of astronomy: theoretical and computational planetary astronomy, spherical astronomy and time keeping, instrumentation, and folk astronomy.