Abu Mahmud Hamid ibn Khidr Khojandi (known as Abu Mahmood Khojandi, Alkhujandi or al-Khujandi,
Persian: ابومحمود خجندی, c. 940 - 1000) was a
Central Asian astronomer and mathematician who lived in the late 10th century and helped
build an observatory, near the city
of Ray (near today's Tehran), in Iran.
He was born in Khujand; a bronze
bust of the astronomer is present in a park in modern-day Khujand, now part
of Tajikistan.
Astronomy
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.
Mathematics
Khojandi
stated a special case of Fermat's last theorem 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, Abul
Wafa or Nasir al-Din al-Tusi discovered it first.
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