Al-Battani (known in Latin as Albategnius) was a ninth-century Muslim astronomer and mathematician from Harran, in what is now Turkey. He is often described as one of the greatest observers of the medieval Islamic world. Working mostly in Raqqa, Syria, he spent about four decades watching the Sun, Moon and planets, and wrote an astronomical handbook that was still being read in Europe some 700 years later. Britannica notes that he was the best-known Arab astronomer in medieval Europe. In this article we look at his life, his instruments, his results and his lasting influence.
Quick facts
| Full name | Abu Abdallah Muhammad ibn Jabir ibn Sinan al-Raqqi al-Harrani al-Sabi al-Battani |
| Born | Before 858 (Britannica says c. 858; MacTutor says about 850), in or near Harran, Upper Mesopotamia (now Turkey) |
| Died | 929, at Qasr al-Jiss near Samarra, Iraq |
| Fields | Astronomy, mathematics (trigonometry), instrument use, astrology (as practised in his time) |
| Most famous work(s) | Kitab al-Zij (also called al-Zij al-Sabi, “The Sabian Tables”); Latin title De motu stellarum |
| Known for | Very accurate long-term observations; improved values for the year, the ecliptic and precession; showing that annular solar eclipses are possible |
Early life in Harran
Harran was an old city on the Balikh River, and it was home to the Sabians, a star-worshipping religious community that produced several well-known scholars, including Thabit ibn Qurra. According to MacTutor and the Biographical Encyclopedia of Astronomers, al-Battani was born into a Sabian family but was himself a Muslim. Historians infer this from his name: Muhammad, with the kunya Abu Abdallah.
Historians think his father was Jabir ibn Sinan al-Harrani, a respected instrument maker. The identification is probable rather than completely certain. If it is right, al-Battani likely learned about astronomical instruments from his father before moving to Raqqa. Our knowledge of his life is thin. The main early sources are Ibn al-Nadim (died 990) and al-Qifti.
One old claim is worth correcting. European books until the 19th century often called him a prince or king. The Biographical Encyclopedia of Astronomers says there is no support for this in the Arabic sources.
The private observatory at Raqqa
Raqqa lies on the Euphrates and had grown prosperous after Caliph Harun al-Rashid built palaces there. According to the Biographical Encyclopedia of Astronomers, al-Battani spent considerable personal funds on a private observatory. He observed regularly there from 877 to 918. That is about 40 years of steady work, which is rare in any age.
The same source lists the instruments he is known to have used:
- a gnomon (a vertical pointer that casts a shadow)
- horizontal and vertical sundials
- a triquetrum and parallactic rulers
- an astrolabe
- a new type of armillary sphere
- a mural quadrant with an alidade
For several of these, he recommended sizes of more than a metre, because larger instruments allow finer readings. He also made observations at Antioch, where in 901 he observed a solar and a lunar eclipse.
The Kitab al-Zij: his great handbook
A zij is an astronomical handbook with tables. Al-Battani’s Kitab al-Zij is by far his most important work. MacTutor says it has 57 chapters. They cover the zodiac and its degrees, the mathematical tools needed (including trigonometric functions), his own observations, planetary motions, how to read the tables, astrological problems, the making of a sundial and the construction of instruments.
The book is practical in spirit. The Biographical Encyclopedia of Astronomers notes that about a third of it is tables, and most of the text tells the reader how to use them for real calculations. It follows Ptolemy’s tradition but is written in clear Arabic with very little foreign technical vocabulary. Ibn al-Nadim, writing in the 10th century, said nobody in Islam was known to match his perfection in observing the stars.
Measuring the year, the stars and the sky
According to MacTutor, his results include:
- Length of the year: 365 days, 5 hours, 46 minutes and 24 seconds.
- Star catalogue: 489 stars, based on the year 880.
- Precession of the equinoxes: 54.5 arcseconds per year.
- Tilt of the ecliptic (obliquity): 23° 35′.
The Biographical Encyclopedia of Astronomers adds that the true tilt in 880 was 23° 35′ 6″, so his value was extremely close. It also says he found the latitude of Raqqa as 36° 1′, against a modern value of 35° 57′. The same source says the accuracy of his equinox and solstice observations was not much inferior to Tycho Brahe’s, about 700 years later. His careful construction and alignment of large instruments, and a clever way of combining repeated observations, probably explain this.
His star table was made by adding a precession correction to Ptolemy’s star positions. It contains roughly half as many stars as the Almagest. So it was a carefully updated table rather than a brand-new survey of the whole sky.
Correcting Ptolemy and using trigonometry
Al-Battani respected Ptolemy but did not simply copy him. The school-level summary from the Schools’ Observatory says he checked earlier work against his own observations and corrected mistakes. MacTutor quotes the historian Willy Hartner: al-Battani generally accepted Ptolemy’s overall model, but he corrected Ptolemy’s practical results, including the idea that the Sun’s apogee and the ecliptic’s tilt never change. Britannica says he showed the Sun’s apogee, its farthest point from Earth, is variable.
He also studied the apparent sizes of the Sun and Moon. From this, he concluded that annular solar eclipses are possible. These are eclipses where a ring of the Sun remains visible.
Mathematically, Britannica says he improved Ptolemy’s calculations by replacing geometrical methods with trigonometry. MacTutor gives a right-angled triangle formula from his work, which is equivalent to a modern sine rule used for shadow problems. One caution: a small treatise on sines attributed to him has had its authenticity questioned by scholars. So his trigonometry is best judged from the Zij itself.
His last journey
Sources agree on the broad outline of his death but differ on the reason for his trip. MacTutor, citing the Fihrist, says he travelled to Baghdad to protest on behalf of people from Raqqa who had been unfairly taxed. He died on the way back. The Biographical Encyclopedia of Astronomers, also citing Ibn al-Nadim, mentions instead financial difficulties linked to dealings with a Raqqa family. Either way, he died at Qasr al-Jiss near Samarra in 929.
Legacy
- Translations: According to Britannica, the Zij was translated into Latin around 1116 and into Spanish in the 13th century. Plato of Tivoli’s Latin version was printed at Nuremberg in 1537 and again at Bologna in 1645.
- Later astronomers in the Islamic world: Al-Biruni wrote a treatise on al-Battani’s Zij, now lost. Later zijes, such as those of Kushyar ibn Labban and al-Nasawi, used his mean-motion values.
- European science: The Biographical Encyclopedia of Astronomers says Regiomontanus, Copernicus, Tycho Brahe, Kepler and Galileo made use of his work.
- Eclipse records: In the 18th century, Richard Dunthorne used his eclipse observations to study the Moon’s secular acceleration.
- On the Moon: The lunar crater Albategnius is named after him, as MacTutor lists among his honours.
Frequently asked questions
Who was Al-Battani?
Al-Battani was a Muslim astronomer and mathematician (died 929) from Harran who observed the heavens at Raqqa for about 40 years. He is best known for his Kitab al-Zij, a book of astronomical tables and methods.
What did Al-Battani discover?
He refined the length of the year, the tilt of the ecliptic and the rate of precession. He showed that the Sun’s apogee moves and that annular solar eclipses can occur. He also used trigonometry in place of Ptolemy’s geometrical methods. Some of these points built on earlier work, such as the findings of the astronomers of Caliph al-Ma’mun, which he confirmed.
Did Copernicus use Al-Battani’s work?
Yes. Both MacTutor and the Biographical Encyclopedia of Astronomers list Copernicus among the European scholars who used his work.
Read more: Explore the full Great Muslim Scientists series, including Nasir al-Din al-Tusi: The Polymath of Maragheh Who Made Trigonometry a Science and Al-Biruni: The Scholar Who Measured the Earth.
Sources: Encyclopaedia Britannica – al-Battani; MacTutor, University of St Andrews – Al-Battani; Biographical Encyclopedia of Astronomers (Springer), via McGill University – Battani
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