| Habash al-Hasib | |
| Native Name: | حبش الحاسب |
| Native Name Lang: | fa |
| Birth Name: | Ahmad ibn ‘Abdallah al-Marwazi |
| Birth Place: | Merv, Abbasid Caliphate |
| Death Date: | Between 864–874 (aged 100) |
| Death Place: | Possibly in Abbasid Samarra, Abbasid Caliphate |
| Known For: | Kepler's equation |
| Children: | Abu Ja'far ibn Habash |
| Fields: | Astronomy |
Ahmad ibn 'Abdallah al-Marwazi,[1] known as Habash al-Hasib ([2] died 869) was a Persian[3] [4] astronomer,[5] geographer, and mathematician from Merv in Khorasan, who was the first to describe the trigonometric ratios tangent, and cotangent. Al-Biruni who cited Habash in his work, expanded his astronomical tables.
Habash al-Hasib flourished in Baghdad, and died a centenarian some time between 864–874[6] possibly in Abbasid Samarra. The title "Habash" (Abbyssian) may refer to dark skin coulor. He worked under two Abbasid caliphs, al-Ma'mun and al-Mu'tasim.
Habash al-Hasib developed a trigonometric algorithm to solve problems related to parallax, which was later rediscovered by Johannes Kepler in 1609 and it is now known as Kepler's equation.[7] [8]
Habash is the father of the astronomer Abu Ja'far ibn Habash.
Habash Hasib made astronomical observations from 825 to 835, and compiled three zijes (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 was generally adopted by Muslim astronomers.
In 830, he 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. He also introduced the cotangent, and produced the first tables of for it.[9] [10]
Habash al-Hasib conducted various observations at the Al-Shammisiyyah observatory in Baghdad and estimated a number of geographic and astronomical values. He compiled his results in The Book of Bodies and Distances, in which some of his results included the following:
3207.275 miles (5161.609 km)