Mathematician,
astronomer and astrologist (B.? – D. The first quarter of the XI. Century). His
full name was Kiyâ Ebu’l-Hasen Kûşyâr b. Lebbân b. Bâşehrî el-Cilî.
He was from a family that went to Bagdad from
the region of Gilan (Cîlân) in the north of the Caspian Sea and
there is no information about his life. The fact that he gave the position of
some fixed stars in the year of
Kûşyâr
was one of the notable names of his period in the field of mathematics,
astronomy and astrology as his sobriquet “Kiyâ” having the meaning of “master”
indicates. He processed systematically the calculation realized through
the Hindu numerals and the numeration system to the base sixty (hisâb-ı sittinî) (this
calculation was a sub-branch of the science of astronomy) in his written work “Kitâb lî uşûli’l-hisâbi’i-Hindî”.
This work was one of the oldest written works in its field that arrived to the present
day and its most important characteristic is that it transmitted the Hindu
mathematics numbers and methods for the first time to the astronomic
calculation system according to the identifications made until now. Within this
context, he successfully implemented and developed the algorithmic calculation
technique of Harizmî both in the Hindu calculation and in the numeration system
to the base sixty (hisâb-ı sittînî), especially in the calculation
of square and cube root. Besides, the fact that he indicated that the results
in some divisions and square root operations were continuous, showed that he
approached to the decimal fraction system.
The
calculation techniques put forward in this work of Kûşyâr were developed by Ali
b. Ahmed en-Nesevî, who was accepted as his student. Kûşyâr dealt with the topics
of calendar, planar and globular trigonometric functions, star tables etc. in
his written work named “ez-Zîcü’l-câmi”. Within this context, he reviewed the
trigonometric information put forward before him. As a matter of fact, while
Ebü’l-Vefâ el-Buzcânî gave only the table of sinus and Bettânî
only the tables of sinus and cotangent, Kûşyâr has given the tables of sinus,
contingent, tangent and versed-sinus together with the differences between
them. As for the calculations of the trigonometric functions, he continued them
until three digits in the system to the base sixty and calculated the angles by
increasing them by one degree. Besides, Kûşyâr is accepted as
the inventor and the eponym of “şekl-i muğnî”(T.N. “rich form”)in
the Islamic trigonometry history as Birûnî firstly mentioned in his written
work “Ma-kâlîdü
ilmi’l-heye” and Nasirüddin-i
Tusî repeated it in his book “Kitâ-bü
Şekli’l-kattâ”. The
written work of Kûşyâr named “Kitâbü’l-Medhal fî şınâ ati ahkâmi’n-nücûm” is
one of the most famous written works of the East in the field of astrology, it was
translated to Turkish, Persian and Chinese and it turned into a reference book.
The written work was an exceptionally systematical work that contained Persian
and Hindu astrology studies, as well as his own opinions, together with the
book “Tetrabiblos” of Batlamyus.
Kûşyâr’s
written works are: “Risâletü’l-eb ad ve el-ecrâm,
Tecrîdü uşûli terkî-bi’I-cüyûb, Kitâbü’l-Usturlâb
ve keyfiyyeti amelihî ve i’tibârihî ale’t-tamâm
ve’I-kemâl (He also had
some written works known with the name Kitâbü’l-Usturtâb and İrşâd-i Usturlâb (translated into Persian). Beyhaki indicated that
some engineers had criticized Kûşyâr about the subject of the planet Mars and
that he had written a work named “Isla
hu ta’dîli’l-Mirrîh”. Kâtip Çelebi
recorded that Kûşyâr had owned a written work named “Kitâbü’l-Kiyâ fi’n-nücûm”. Bağdatlı İsmail Pasha attributed him a written work named “Kitâbü’l-Lâmi
fî em-şileti’z-zîci’i-câmi”. This work was created with the explanation of each chapter of “ez-Zîcü’l-câmi” with examples. There was the record that Kûşyâr also
had the written works named “Kitâbü’l-Kırânât”, “Risâle fî delâleti’l-kevâkib”
and “Kitâbü’l-İhtiyârât” in some libraries.
WORKS:
ez-Zîcü'l-câmi (composed of four divisions and
classified among the astronomic books named as “the Group of Bettanî”, because
Kûşyâr, who didn’t make direct astronomic observation, completed many
deficiencies of this written work by taking the principle information from the
“ez-Zîcü’ş-Şâbî” of Bettanî as Şemsülmüneccim Muhammed Ali Hoca indicated in
the preface of “Zîcü'l-muhakkı’s-sultânî ale’r-raşadi’l-İlhânî”), ez-Zîcü’l-bâliğ (only the copy including
the first two chapters of the book survived until today. Edward S. Kennedy
tells that the written work was the summarized copy of ez-Zîcü'l-câmi), Kitâbü’l-Medhal fî sinati ahkâmı’n nücûm
(also known as el-Mücmel fî
şınâ’âti’n-nücûm), Kitâb fî
uşûli’l-hisâbi’l-Hindî (Şâlöm b. Joseph Anâbî made it translated to Hebrew
language in the years of 1450-
REFERENCE: Sâlih Zeki / Âsâr-ı Bâkıye (s. 166-167, 1911), İhsan Fazlıoğlu / TDV
İslâm Ansiklopedisi (c.26, 2002), İhsan Işık / Ünlü Bilim Adamları (Türkiye Ünlüleri Ansiklopedisi,
C. 2, 2013) - Encyclopedia of Turkey’s Famous People (2013).