In 711 CE, Muslims arrived in Spain under the leadership of Tariq bin Ziyad, a companion of the Prophet’s followers. Over time, through various rulers, Al-Andalus flourished into a center of civilization. Inspired by an unrelenting passion for knowledge, Muslims in Al-Andalus engaged in scholarly pursuits comparable to those in Baghdad. The establishment of an independent Muslim rule in Spain began in 756 CE with the ascension of Abd al-Rahman I. Under his successors, particularly Abd al-Rahman II (822–852 CE) and Abd al-Rahman III (916–961 CE), Spanish Muslim civilization reached its intellectual and scientific zenith.

Before the arrival of Muslims, Spain’s astronomical knowledge was largely based on Ptolemaic discoveries and Greek science. However, the pre-Islamic inhabitants of the region primarily used limited astronomical knowledge for astrology, religious prophecies, magic, and supernatural practices. In contrast, Islamic astronomy was rooted in scientific precision and the meticulous study of celestial phenomena, making it widely embraced in Spain.

During the reign of Abd al-Rahman III, significant progress in astronomy took place. A group of scholars, trained under the Abbasid Caliphate, established a center for research in Córdoba, where they conducted extensive studies in astronomy, mathematics, and meteor science. Among them, the most distinguished figure was Maslama ibn Ahmad al-Majriti (950–1007 CE), who became one of the leading astronomers of Al-Andalus. Originally from another region, Al-Majriti migrated to Córdoba at a young age, where he studied astronomical observations under the geo-mathematician Abd al-Ghafir bin Muhammad. His works were deeply influenced by Al-Khwarizmi’s writings, which played a significant role in shaping his research.

One of his most notable contributions was the relocation of the prime meridian (Dhruvarekha) from Ujjain, India, to Córdoba, marking a major shift in the reference system for astronomical calculations. He also developed numerous astronomical maps based on the study of light rays, achieving results more precise than Al-Khwarizmi’s earlier findings. Apart from astronomy, Al-Majriti also wrote on commercial arithmetic, addressing topics such as trade, taxation, and financial calculations. He prepared an Arabic translation of Ptolemy’s star catalog, Planisphaerium, making classical Greek astronomical knowledge more accessible to scholars in the Islamic world.

Al-Majriti’s influence extended through a remarkable generation of students who continued advancing Islamic astronomical and mathematical sciences. His most notable disciples included Hamid al-Din al-Kirmani, Ibn al-Samh, and Ibn al-Saffar. Among them, Ibn al-Samh made a significant contribution to the study of astronomical instruments, authoring a 130-chapter book on the astrolabe, further cementing Al-Andalus’ status as a leading center for scientific inquiry in the medieval world.

Abu Ishaq Ibrahim al-Zarqali and the Advancement of Astronomy in Muslim Spain

Following Al-Majriti, another major figure in the field of astronomy in Muslim Spain was Abu Ishaq Ibrahim al-Zarqali (1029–1100 CE). He initiated a new phase in astronomical research, significantly shaping the discipline. Unlike many other scholars, Al-Zarqali was largely self-taught. His early career began with crafting astronomical instruments, and his extraordinary intelligence and creativity soon gained recognition. Impressed by his skills, his patrons provided him with opportunities to pursue research in astronomy. Through meticulous observation, he documented the movements of the sun, moon, planets, and stars, leaving behind an extensive body of work. One of his most notable engineering contributions was designing and constructing the famous water clock in Toledo, a marvel of precision and mechanics.

Al-Zarqali made significant advancements in the study of astronomical instruments, particularly the equatorium, an instrument used to calculate the positions of the moon, sun, and planets. He authored two major works on this subject. Following the Muslim loss of Spain, his works were translated into Spanish in the 13th century under the orders of King Alfonso X, ensuring their preservation and dissemination among European scholars.

His research was characterized by rigorous analysis and precise calculations. Recognizing the need for long-term empirical data, he organized a team of astronomers, including both Muslim and Jewish scholars, and conducted systematic sky observations over several years. One of his most important contributions was the compilation of the Toledan Tables in 1080 CE, an astronomical reference guide that became widely used in both the Islamic and European worlds. Although the original Arabic version of this text has been lost, its Latin translation remains available. Alongside Al-Khwarizmi’s works, the Toledan Tables became one of the most widely studied astronomical texts in Europe from the 12th century onward. Despite the fact that his findings were more precise than those of Al-Khwarizmi, both scholars’ works were extensively utilized by astronomers in England, France, and Italy throughout the Middle Ages.

In 1080 CE, Al-Zarqali authored another significant work, A Comprehensive Treatise on the Sun. For this study, he meticulously observed the sun for twenty-five years, recording detailed measurements and patterns. While earlier astronomers believed that the moon’s position in its orbit remained fixed, Al-Zarqali observed and documented lunar motion shifts, a discovery that was later confirmed by the scientific community. His findings on solar motion were discussed in the 16th century by Copernicus, demonstrating the lasting impact of his research. In 1085 CE, he wrote another treatise on the stars, further solidifying his reputation as one of the most advanced astronomers of his time.

His contributions extended beyond solar and lunar studies. Over thirty years, he systematically observed the moon’s motion, producing highly accurate records. He also wrote a comprehensive book on the movement and influence of planets, which became a valuable resource for later scholars. Recognizing the importance of preserving Islamic knowledge, King Alfonso X of Galicia (r. 1252–1284 CE) sought to translate key scientific works from Arabic into Spanish. He established a translation school dedicated to this purpose, ensuring that Al-Zarqali’s writings, among others, were preserved and further studied. This transmission of knowledge laid the foundation for scientific progress in Europe and played a critical role in shaping the European Renaissance.

Astronomy: Persian Contributions

While the Abbasid caliphs in Baghdad were pioneering revolutionary discoveries in astronomy, similar advancements were unfolding in Persia. One of the most prominent Persian contributors to this field was Abd al-Rahman al-Sufi (903–986 CE). He served at the court of Abu Dawla, a ruler from the Buyid dynasty, which governed parts of Iran and Iraq during the 9th and 10th centuries. The Buyid rulers, who had united various tribal factions under a centralized Muslim administration, displayed a deep interest in astronomical research.

Like many astronomers before him, Al-Sufi focused on revising and expanding upon Ptolemy’s observations. One of his most significant achievements was his revision of Ptolemy’s star catalog, which he meticulously refined and updated. In 964 CE, he compiled his findings into a book titled Kitāb al-Kawākib al-Thābita (The Book of Fixed Stars), which served as an essential astronomical reference. This work synthesized and compared Greek astronomical theories with new observations made by Muslim astronomers, making it one of the most comprehensive works of its time.

The Buyid dynasty continued its patronage of astronomy under the reign of Sharaf al-Dawla, who established a dedicated astronomical observatory. The primary objective of this research center was to study and document the movements of the seven visible celestial bodies—the sun, the moon, and the five visible planets. The observatory was a grand architectural structure equipped with the most advanced astronomical instruments available at the time, making it one of the most sophisticated facilities in the Islamic world.

A leading Persian astronomer of this period was Abu Mahmud al-Khujandi (940–1000 CE), who played a vital role in advancing astronomical observations under the patronage of the Buyid rulers. His most notable contribution was the design and construction of a massive meridian arc, which had a diameter of twenty meters—one of the largest instruments of its kind ever built. His innovations marked a significant leap in the accuracy of celestial measurements, further cementing Persia’s place as a center of astronomical excellence during the medieval Islamic era.

Omar Khayyam: Poet, Mathematician, and Astronomer

One of the most significant astronomers to emerge in the later period was Omar Khayyam. Though he later became renowned as a poet, Khayyam was also an accomplished mathematician, astronomer, and philosopher (1048–1131 CE). Born in Nishapur, Iran, he received his early education there before traveling to Samarkand in 1070 CE, where he wrote his first major work, A Book on Algebra. In this treatise, he not only recorded his observations but also incorporated arguments from Indian mathematical traditions, demonstrating his engagement with diverse intellectual influences. His second significant work was an explanation of Euclidean mathematical principles, reflecting his deep engagement with Greek geometry.

In 1074 CE, during the reign of Malik Shah I, Khayyam was invited to the royal court in Isfahan and was appointed chief astronomer. Earlier astronomers had lacked access to advanced observational equipment, which limited the accuracy of their research. To overcome this, Malik Shah commissioned the construction of a grand observatory, placing Khayyam in charge. He was joined by six other astronomers, and together they worked to update and refine the astronomical findings recorded in Ptolemy’s Almagest. Khayyam fully devoted himself to this project, and one of his most significant contributions during this period was the proposal of a new solar calendar, later known as the Jalali Calendar. This new calendar gained wide recognition due to its improved accuracy compared to previous systems.

Khayyam also authored two significant works on astronomy. In Malik Shah’s Astronomical Treatises, he categorized the hundred brightest stars, a project that took him and his colleagues fifteen years to complete. However, after Malik Shah’s death in 1092 CE, his successors showed little interest in Khayyam or his astronomical research, leading to the decline of further investigations in this field. Khayyam continued his scholarly pursuits in Isfahan, where he later authored The History of the New Year, a work that examined the measurement of time and the progression of calendars. In addition, he wrote Tarikh-i-Falaki (The Chronology of the Heavens) in Persian, further solidifying his legacy in the field of astronomy and timekeeping.

Abd al-Rahman al-Khazini: A Leading Astronomer of Persia

Another distinguished astronomer who rose to prominence in Persia was Abd al-Rahman al-Khazini, who lived during the reign of Sultan Ahmad Sanjar (1118–1153 CE). His most significant work, titled A Special Astronomical Book Dedicated to Sultan Sanjar, became a landmark text in the study of astronomy. This book was enriched with numerous new astronomical observations, reflecting his meticulous approach to celestial studies. Al-Khazini spent several years observing the sun, the moon, and the five visible planets, systematically analyzing their characteristics and comparing his findings with those of earlier scholars. In the introductory section of his work, he provided a detailed discussion on different calendar systems, explaining the Islamic Hijri calendar alongside those used by Jews, Hindus, and Christians, highlighting their differences and applications. His research also led to the development of new planetary tables, which provided improved calculations of planetary positions.

Beyond astronomy, Al-Khazini made important contributions to the study of gravity and astronomical instruments. His writings explored the principles of gravitational force, a subject that would later influence medieval European scholars. He also designed instruments that helped enhance naked-eye observations of celestial bodies, improving the precision of astronomical measurements. One of his most notable inventions was a celestial globe that mapped the stars and their orbits, demonstrating his expertise in both theoretical and practical aspects of astronomy.

The influence of Al-Khazini’s works extended beyond the Islamic world. In 1290 CE, the Orthodox Christian bishop Gregory Chioniades traveled to Tabriz, where he translated Al-Khazini’s writings into Greek. This translation played a crucial role in generating interest in astronomy among scholars in Constantinople, marking an important phase in the transmission of Islamic scientific knowledge to medieval Europe.