Abu Sa'id Ahmed ibn Mohammed ibn Abd al-Jalil al-Sijzi (c. 945 - c. 1020, also known as al-Sinjari and al-Sijazi; fa, ابوسعید سجزی; Al-Sijzi is short for " Al-Sijistani") was an Iranian Muslim astronomer,

mathematician A mathematician is someone who uses an extensive knowledge of mathematics in their work, typically to solve mathematical problems. Mathematicians are concerned with numbers, data, quantity, mathematical structure, structure, space, Mathematica ...

, and

astrologer Astrology is a range of divinatory practices, recognized as pseudoscientific since the 18th century, that claim to discern information about human affairs and terrestrial events by studying the apparent positions of celestial objects. Di ...

. He is notable for his correspondence with al-Biruni and for proposing that the Earth rotates around its axis in the 10th century. He dedicated work to

'Adud al-Daula Fannā (Panāh) Khusraw ( fa, پناه خسرو), better known by his laqab of ʿAḍud al-Dawla ( ar, عضد الدولة, "Pillar of the bbasidDynasty") (September 24, 936 – March 26, 983) was an emir of the Buyid dynasty, ruling fro ...

, who was probably his patron, and to the prince of Balkh. He also worked in Shiraz making astronomical observations from 969 to 970.

Mathematics

Al-Sijzi studied intersections of conic sections and circles. He replaced the old kinematical trisection of an angle by a purely geometric solution (intersection of a circle and an equilateral hyperbola.)

Earth's rotation

Al-Biruni tells us that Al-Sijzi invented an

astrolabe An astrolabe ( grc, ἀστρολάβος ; ar, ٱلأَسْطُرلاب ; persian, ستاره‌یاب ) is an ancient astronomical instrument that was a handheld model of the universe. Its various functions also make it an elaborate incli ...

, called "al-zūraqī", whose design was based on the idea that the Earth rotates: Al-Biruni also referred to Al-Sijzi as a prominent astronomer who defended the theory that the earth rotates in ''al-Qānūn al-Masʿūdī''."ʾaḥad al-mubrazīn fī ʿilm al-hayʾa" The fact that some people did believe that the earth is moving on its own axis is further confirmed by a reference from the 13th century which states:

"According to the geometers
r engineers R, or r, is the eighteenth letter of the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''ar'' (pronounced ), plural ''ars'', or in Irel ...
(''muhandisīn''), the earth is in constant circular motion, and what appears to be the motion of the heavens is actually due to the motion of the earth and not the stars."

Notes

References

* * * Suter, Heinrich: Die Mathematiker und Astronomen der Araber und ihre Werke (80–81, 224, 1900).

External links

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* Medieval Iranian astrologers 10th-century Iranian mathematicians 11th-century Iranian mathematicians 940s births 1020 deaths Year of birth uncertain 10th-century Iranian astronomers Scholars under the Buyid dynasty 10th-century inventors 11th-century Iranian astronomers {{Asia-mathematician-stub