Communication
Caliph Al Ma'mun [b. Baghdad, 786, d. Tarsus, Cilicia, August 833] founds The "House of Wisdom" in Baghdad, a center for study and research similar to the earlier Museum in Alexandria. Its most famous scholars are the mathematicians Muhammad ibn Musa Al-Khwarizmi [b. Khwarizm (Uzbekistan), c. 780, d. c. 850] and the Banu Musa ("sons of Moses"), three brothers who direct the translation of Greek works from Antiquity. See also 815 Communication; 850 Tools.
Earth scienceIn his world geography, based largely on Ptolemy, Al-Khwarizmi overestimates the size of Earth, giving it a circumference of 64,000 km (40,000 mi). See also 140 ce Earth science.
MathematicsAl-Khwarizmi about this time writes De numero indorum ("concerning the Hindu art of reckoning"), which gives a set of rules for computing with Hindu-Arabic numerals. This work, when translated, introduces Hindu-Arabic notation to Europe. See also 775 Mathematics; 835 Mathematics.
ToolsMuhammad Al-Khwarizmi about this time describes the astrolabe, which he probably learns of from Hellenic sources. It is used to find rising and setting times for a celestial body, the altitude of the body above the horizon, and the body's azimuth (position along the horizon as measured from true north). See also 400 ce Tools; 1210 Tools.
