Abu Mahmud Hamid ibn al-Khidr al-Khojandi (known as Abu Mahmood Khojandi, Alkhujandi or al-Khujandi, Persian: ابومحمود خجندی, c. 940 - 1000) was a Muslim Transoxanian

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

and

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 ...

born in

Khujand Khujand ( tg, Хуҷанд, Khujand; Uzbek: Хўжанд, romanized: Хo'jand; fa, خجند‌, Khojand), sometimes spelled Khodjent and known as Leninabad (russian: Ленинабад, Leninabad; tg, Ленинобод, Leninobod; fa, لنی ...

(now part of

Tajikistan Tajikistan (, ; tg, Тоҷикистон, Tojikiston; russian: Таджикистан, Tadzhikistan), officially the Republic of Tajikistan ( tg, Ҷумҳурии Тоҷикистон, Jumhurii Tojikiston), is a landlocked country in Centr ...

) who lived in the late 10th century and helped build an observatory, near the city of Ray (near today's

Tehran Tehran (; fa, تهران ) is the largest city in Tehran Province and the capital of Iran. With a population of around 9 million in the city and around 16 million in the larger metropolitan area of Greater Tehran, Tehran is the most popul ...

), in

Iran Iran, officially the Islamic Republic of Iran, and also called Persia, is a country located in Western Asia. It is bordered by Iraq and Turkey to the west, by Azerbaijan and Armenia to the northwest, by the Caspian Sea and Turkmeni ...

Astronomy

Khojandi worked under the patronage of the Buwayhid Amirs at the observatory near

Ray, Iran Shahr-e Ray ( fa, شهر ری, ) or simply Ray (Shar e Ray; ) is the capital of Ray County in Tehran Province, Iran. Formerly a distinct city, it has now been absorbed into the metropolitan area of Greater Tehran as the 20th district of municip ...

, where he is known to have constructed the first huge mural sextant in 994 AD, intended to determine the Earth's

axial tilt In astronomy, axial tilt, also known as obliquity, is the angle between an object's rotational axis and its orbital axis, which is the line perpendicular to its orbital plane; equivalently, it is the angle between its equatorial plane and orb ...

("obliquity of the ecliptic") to high precision. He determined the axial tilt to be 23°32'19" for the year 994 AD. He noted that measurements by earlier astronomers had found higher values (Indians: 24°;

Ptolemy Claudius Ptolemy (; grc-gre, Πτολεμαῖος, ; la, Claudius Ptolemaeus; AD) was a mathematician, astronomer, astrologer, geographer, and music theorist, who wrote about a dozen scientific treatises, three of which were of importance ...

23° 51') and thus discovered that the axial tilt is not constant but is in fact (currently) decreasing. His measurement of the axial tilt was however about 2 minutes too small, probably due to his heavy instrument settling over the course of the observations.

Mathematics

Khojandi stated a special case of

Fermat's Last Theorem In number theory, Fermat's Last Theorem (sometimes called Fermat's conjecture, especially in older texts) states that no three positive integers , , and satisfy the equation for any integer value of greater than 2. The cases and have been ...

for n = 3, but his attempted proof of the theorem was incorrect. The spherical law of sines may have also been discovered by Khujandi, but it is uncertain whether he discovered it first, or whether

Abu Nasr Mansur Abu Nasri Mansur ibn Ali ibn Iraq ( fa, أبو نصر منصور بن علی بن عراق; c. 960 – 1036) was a Persian Muslim mathematician and astronomer. He is well known for his work with the spherical sine law.Bijli suggests that three ...

, Abul Wafa or Nasir al-Din al-Tusi discovered it first.Bijli suggests that three mathematicians are in contention for the honor, Alkhujandi, Abdul-Wafa and Mansur, leaving out Nasiruddin Tusi. Bijli, Shah Muhammad and Delli, Idarah-i Adabiyāt-i (2004) ''Early Muslims and their contribution to science: ninth to fourteenth century'' Idarah-i Adabiyat-i Delli, Delhi, India, page 44,

Notes

References

External links

*
PDF version
*

{{DEFAULTSORT:Khujandi 940s births 1000 deaths 10th-century Iranian astronomers Inventors of the medieval Islamic world Scientific instrument makers Scholars under the Buyid dynasty 10th-century inventors 10th-century Iranian mathematicians