Abu Rayhan al-Biruni (973-ca. 1050), a Moslem astronomer, mathematician, geographer, and historian, was the most acute interpreter of India to Islam in the Middle Ages.

Al-Biruni was born near Kath in Khwarizm (now a part of Uzbekistan) on Sept. 4, 973. His teacher in astronomy and mathematics was the eminent Abu Nasr Mansur, a member of the family then ruling at Kath. Al-Biruni made several observations with a meridian ring at Kath in his youth. In 995 the attack on the ruler of Khwarizm by the ruler of Jurjaniya drove al-Biruni into exile, presumably to Rayy, where he discussed with the astronomer al-Khujandi the latter's observations with a mural sextant. AlBiruni later wrote a treatise on this instrument and gave a detailed account of the observations in his Tahdid.

In 997 al-Biruni returned to Kath, where he observed a lunar eclipse that Abu al-Wafa observed in Baghdad; on the basis of the time...