Al-Battani

Al-Battānī
A modern artist's impression of al-Battānī holding an astrolabe
Born	c. 858 CE Harran, Bilad al-Sham
Died	929 CE Qasr al-Jiss, near Samarra
Residence	Caliphate
Academic background
Influences	Ptolemy
Academic work
Era	Islamic Golden Age
Main interests	Mathematics, Astronomy, Astrology
Notable works	Kitāb az-Zīj
Notable ideas	Trigonometrical relationships
Influenced	Abū al-Wafā', al-Bīrūnī, Copernicus

Abū ʿAbd Allāh Muḥammad ibn Jābir ibn Sinān al-Raqqī al-Ḥarrānī aṣ-Ṣābiʾ al-Battānī (Arabic: محمد بن جابر بن سنان البتاني) (Latinized as Albategnius, Albategni or Albatenius) (c. 858 – 929) was an Arab astronomer, astrologer, and mathematician. He introduced a number of trigonometric relations, and his Kitāb az-Zīj was frequently quoted by many medieval astronomers, including Copernicus.

Little is known about al-Battānī's life beside that he was born in Harran near Urfa, in Upper Mesopotamia, which is now in Turkey, and his father was a famous maker of scientific instruments. His epithet aṣ-Ṣabi’ suggests that among his ancestry were members of the Sabian sect; however, his full name indicates that he was Muslim. Some western historians state that he is of noble origin, like an Arab prince, but traditional Arabic biographers make no mention of this. He lived and worked in ar-Raqqah, a city in north central Syria.

One of al-Battānī's best-known achievements in astronomy was the determination of the solar year as being 365 days, 5 hours, 46 minutes and 24 seconds which is only 2 minutes and 22 seconds off.

He was able to correct some of Ptolemy's results and compiled new tables of the Sun and Moon, long accepted as authoritative. Some of his measurements were even more accurate than ones taken by Copernicus many centuries later. Researchers have ascribed this phenomenon to al-Battānī being in a geographical location that is closer to the southern latitude, which might have been more favorable for such observations.

Al-Battānī discovered that the direction of the Sun's apogee, as recorded by Ptolemy, was changing. (In modern heliocentric terms this is due to the changing direction of the eccentricity vector of the Earth's orbit). He also introduced, probably independently of the 5th century Indian astronomer Aryabhata, the use of sines in calculation, and partially that of tangents. He also calculated the values for the precession of the equinoxes (54.5" per year, or 1° in 66 years) and the obliquity of the ecliptic (23° 35'). He used a uniform rate for precession in his tables, choosing not to adopt the theory of trepidation attributed to his colleague Thabit ibn Qurra.