Abu Mahmud Hamid ibn al-Khidr al-Khujandi[1] (known as Abu Mahmood Khujandi, al-khujandi or Khujandi, Persian: ابومحمود خجندی,
c. 940 - 1000) was a Muslim
Transoxanianastronomer and
mathematician born in
Khujand (now part of
Tajikistan) who lived in the late 10th century and helped build an
observatory, near the city of
Ray (near today's
Tehran), in
Iran.
Khujandi worked under the patronage of the
Buwayhid Amirs at the observatory near
Ray, Iran, where he is known to have constructed the first huge
mural sextant in 994 AD, intended to determine the Earth's
axial tilt ("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 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.[2][3]
^Also the 'sine law' (of geometry and trigonometry, applicable to spherical trigonometry) is attributed, among others, to khujandi. (The three others are Abul Wafa Bozjani, Nasiruddin Tusi and Abu Nasr Mansur). Razvi, Syed Abbas Hasan (1991) A history of science, technology, and culture in Central Asia, Volume 1 University of Peshawar, Peshawar, Pakistan, page 358,
OCLC26317600
^Bijli suggests that three mathematicians are in contention for the honor, khujandi, 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,
OCLC66527483