Al-Marwazi

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Ahmad ibn 'Abdallah Habash al-Hasib al-Marwazi (Arabic: أحمد بن عبد الله المروازي حباش الحاسب) was a Persian astronomer and mathematician from Merv in Khorasan, Persia.

He flourished in Baghdad, and died a centenarian between 864 and 874. He worked under the Abbasid caliphs al-Ma'mun and al-Mu'tasim.

He made observations from 825 to 835, and compiled three astronomical tables: the first were still in the Hindu manner; the second, called the 'tested" tables, were the most important; they are likely identical with the "Ma'munic" or "Arabic" tables and may be a collective work of al-Ma'mun's astronomers; the third, called tables of the Shah, were smaller.

Apropos of the solar eclipse of 829, Habash gives us the first instance of a determination of time by an altitude (in this case, of the sun); a method which generally adopted by Muslim astronomers.

He also seems to have introduced the notion of "shadow," umbra (versa), equivalent to our tangent in trigonometry, and he compiled a table of such shadows which seems to be the earliest of its kind.