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Astronomy
 Astronomy may not seem so essential
today, but that is only because we take accurate calendars
and clocks for granted. We scarcely notice the phases of the
moon, the sun’s passage marked by equinoxes (fall and spring
dates of equal daytime and nighttime) and solstices (longest
and shortest days of summer and winter), because they no
longer seem essential to our lives. To get from one place to
another, we use interstate highways and road maps, not
devices for navigating by the stars.
In contrast to us, Medieval societies
made great efforts to establish accurate calendars for
celebration of religious holidays, 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 that tried 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 already questioned Ptolemy’s work,
and made many important calculations. Columbus even used his
figures on the earth’s circumference, but misunderstood the
unit of measurement on which he based his calculations!
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) was another critic of Ptolemy, whose
work 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 and 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. George
Saliba. Rethinking the Roots of Modern Science: Arabic
Scientific Manuscripts in European Libraries, Occasional
Paper, Center for Contemporary Arabic Studies, Georgetown
University, 1999.
George
Saliba. “Whose Science is Arabic Science in Renaissance
Europe?” © George Saliba - Columbia University retrieved at
http://www.columbia.edu/~gas1/project/visions/case1/sci.1.html
Paul
Lunde. Science: The Islamic Legacy. Special Issue,
Aramco World Magazine.
Images:
Discussion of elliptical orbits by al-Bitruji, Escorial
Library, Spain retrieved at
http://www.islamic-study.org/iais-images/Astronomy-00.jpg Eclipse
of the moon by al-Biruni at
http://www.arikah.com/encyclopedia/Al-Biruni
Astrolabe, by Muhammad ibn Sa'id as-Sabban, Guadalajara,
1081/1082, Museum of the History of Science, retrieved at
http://www.mhs.ox.ac.uk/astrolabe/exhibition/52473.htm
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