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 Iranian may refer to: * Iran, a sovereign state * Iranian peoples, the speakers of the Iranian languages. The term Iranic peoples is also used for this term to distinguish the pan ethnic term from Iranian, used for the people of Iran * Iranian lan ...

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, structure, space, models, and change. History On ...

, 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 Abu Rayhan Muhammad ibn Ahmad al-Biruni (973 – after 1050) commonly known as al-Biruni, was a Khwarazmian Iranian in scholar and polymath during the Islamic Golden Age. He has been called variously the "founder of Indology", "Father of Co ...

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 from 9 ...

, who was probably his patron, and to the prince of

Balkh ), named for its green-tiled ''Gonbad'' ( prs, گُنبَد, dome), in July 2001 , pushpin_map=Afghanistan#Bactria#West Asia , pushpin_relief=yes , pushpin_label_position=bottom , pushpin_mapsize=300 , pushpin_map_caption=Location in Afghanistan ...

. He also worked in

Shiraz Shiraz (; fa, شیراز, Širâz ) is the fifth-most-populous city of Iran and the capital of Fars Province, which has been historically known as Pars () and Persis. As of the 2016 national census, the population of the city was 1,565,572 p ...

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 Abu Rayhan Muhammad ibn Ahmad al-Biruni (973 – after 1050) commonly known as al-Biruni, was a Khwarazmian Iranian in scholar and polymath during the Islamic Golden Age. He has been called variously the "founder of Indology", "Father of Co ...

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 inclin ...

, 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 Irelan ...
(''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