In contrast to us, Medieval societies
made great efforts to establish accurate calendars for
celebration of religious holidays and for plowing, planting,
and harvesting. Astronomy was necessary for these practical
reasons. Scientists who gathered this knowledge were also
curious to know more about the celestial bodies that fill
the sky at night, and to understand their relationship to
the sun, the moon, and the earth.
Al-Andalus
was open to knowledge from eastern Muslim lands, where
knowledge from many cultures and religious groups was
gathered together during the 800s CE. Early Muslims absorbed
Indian, Mesopotamian, Persian, Greek, and Roman knowledge of
astronomy.
Among
earlier works that played a large role was a system of
astronomy associated with Ptolemy, a mathematician who lived
around 150 CE in Alexandria, Egypt. His system was widely
believed, but as observations continued, astronomers found
that it couldn’t explain the movement of the planets and the
sun that astronomers observed, since it placed the earth at
the center of the universe.
During
the next 1500 years, astronomers continued their
observations and developed mathematical and mechanical
models to explain this observed movement.
Astronomers working in Muslim lands some Muslim, some
Jewish and some Christian --wrote books with diagrams and
formulas, trying to improve on Ptolemy’s system.
Among
the earliest Muslim astronomers was al-Faraghani (fl. 863
CE), who summarized but questioned Ptolemy’s work
and made many important calculations. Columbus used his
figures on the earth’s circumference, but misunderstood the
astronomer's unit of measurement.
Al-Khwarizmi (ca. 770-840 CE), the famous Persian
mathematician, prepared astronomical charts that were later
translated and further developed in Spain.
Al-Battani (d. 929 CE), another critic of Ptolemy, contributed to solving the puzzle of the heavens, and
whose work was used for centuries. He calculated
astronomical tables (charts on the movement of bodies in the
sky), and helped to develop the branch of mathematics called
trigonometry, which he used to calculate accurate solar and
lunar timekeeping.
Astronomy in Spain built on the work being done in the east.
In Córdoba, Spain, al-Zarqali (1029-1087 CE) prepared
astronomical charts called the
Toledan Tables. He also built and improved on the
astrolabe, a tool with hundreds of uses in astronomy,
navigation, surveying and timekeeping.
Jaber
ibn Aflah (d. 1145 CE) is considered important for his
advancements in trigonometry. Using spherical trigonometry,
he designed a portable celestial sphere. Al-Bitruji (d. 1204
CE) was a leading astronomer who was born in Morocco and
migrated to Seville, where he developed a new theory of the
movement of stars.
Translation of books on mathematics
and astronomy in Spain from Arabic through Hebrew and
Castilian into Latin added to the contributions of
Al-Andalus to advancing astronomy in Europe. Historians of
science have long known about these translations, where
they were published, and which scientists owned these books.
Recently, it has become known that some European scientists
had direct or indirect knowledge of Arabic, and we are
learning that there was more than one path by which learning
was exchanged between East and West.
Further
reading:
Howard
Turner. Science in Medieval Islam. Austin: University
of Texas Press, 1995.
