Ahmad ibn 'Abdallah Habash Hasib Marwazi
Date of death:
Merv produced one of the earliest and greatest scientists of Islam Ahmad ibn 'Abdallah al-Marwazi (Marwazi means from Merv) best known as Habash al-Hasib (the calculator) who flourished in Bagdad and died a centenarian between 864 and 874. He was an astronomer under the Caliphs al-Mamun and al-Muttasim. Habash made observations from 825 to 835 and completed three astronomical tables, the best known being the mumtahin (tested) tables, which may be a collective work of al-Ma'mun's astronomers, for there was a whole team involved in observation at the court at the time. 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 was generally adopted by Muslim astronomers. He seems to have introduced the notion of "shadow," umbra (versa), equivalent to our tangent, and he compiled a table of such shadows which seems to be the earliest of its kind. One of Habash’s son, called Djafar was also a distinguished astronomer and instrument maker.