Who was Al-Biruni?
Al-Biruni was a scholar from Khwarazm who lived in the 10th and 11th centuries. He worked in astronomy, mathematics, geography, history, mineralogy and pharmacy. Few people of his time covered so many fields.
If you search “al-biruni kaun tha” or “al-biruni ke bare mein”, this is the short answer. He was a Khwarazmian scholar who observed the sky, calculated positions on Earth, studied India in its own language and wrote on stones and medicines.
He is best known today for a method of calculating the Earth’s radius from a mountain. The next sections cover his life, his books and that method. They also cover the parts of the story that scholars still argue about.
Al-Biruni’s full name
His full name was Abu’l-Rayhan Muhammad ibn Ahmad al-Biruni. The name “Biruni” is the form used in most writing. Turkish sources spell it Bîrûnî.
In Uzbekistan the name appears as Beruniy. In 1957 the historic town of Kâs, in the Karakalpakstan region of Uzbekistan, was renamed Beruniy in his memory. If you travel in Central Asia, you may see that name on a map.
Where was Al-Biruni born?
He was born in 973 in Kâs, the central town of Khwarazm. This region now lies within Uzbekistan. That answers the common searches “al biruni where from”, “al biruni born where” and “al-biruni ka janm”.
So he was neither Arab nor Indian by birth. He came from Khwarazm, and the town of his birth later took his name.
Timeline
- 973: Born in Kâs, Khwarazm.
- 990: Calculated the latitude of Kâs from observations of the Sun.
- Before 995: Wrote his study of map projections.
- 995: Left his homeland after the ruling dynasty of Khwarazm was overthrown.
- 24 May 997: Observed a lunar eclipse from Kâs and compared timings with Abu’l-Wafa in Baghdad.
- Around 1000: In Gurgan, dedicated al-Athar al-Baqiya to the ruler Qabus.
- 1017: After Mahmud of Ghazni took Khwarazm, his life centered on Ghazni.
- 11th century: Applied his method for the Earth’s radius at Nandana.
- 1025: Wrote Tahdid nihayat al-amakin.
- 1030: Completed Tahqiq ma li’l-Hind.
- 1048 or later: Died in Ghazni. Sources give different years, and the Turkish encyclopedia TDV records 1061 as a possibility.
- 1957: The town of Kâs was renamed Beruniy.
A teenager measuring the Sun
His teacher in mathematics and astronomy was Abu Nasr Mansur ibn Ali ibn Iraq. Abu Nasr came from the ruling family of Khwarazm.
In 990, Al-Biruni was only about 17. He watched the Sun reach its greatest height and used that observation to calculate the latitude of Kâs. Latitude tells you how far north a place lies.
Leaving Khwarazm
In 995 the ruling dynasty of Khwarazm was overthrown. Al-Biruni left his homeland.
Around the year 1000 he was in Gurgan. There he dedicated his chronology, al-Athar al-Baqiya, to Qabus, the Ziyarid ruler.
In 1017 Mahmud of Ghazni took Khwarazm. After that, the center of Al-Biruni’s life was Ghazni, in present-day Afghanistan.
Al-Biruni’s books
People searching “al-biruni books” or “al-biruni ki pustak” usually want a list. These are the works that matter most:
- al-Athar al-Baqiya is a work on chronology. He dedicated it to Qabus.
- Tahdid nihayat al-amakin dates from 1025. It contains methods for finding latitude and longitude, distances between cities and the direction of the qibla.
- Tahqiq ma li’l-Hind was completed in 1030. It covers the religions, social life, sciences and culture of India.
- al-Qanun al-Mas’udi is an astronomy encyclopedia. He dedicated it to the Ghaznavid ruler Mas’ud.
- al-Jamahir collects information on precious stones, minerals and metals.
- al-Saydala fi’l-tibb deals with pharmacy, medicine and botany. It also explains the languages behind the names of drugs.
The list shows how wide his range was. One shelf of his books holds astronomy, a guide to India, a book on gems and a book on medicines.
India and Sanskrit
During his research on India, Al-Biruni learned Sanskrit. That gave him direct contact with Indian astronomy.
His book on India deals with Hindu religions, society, sciences and culture.
Maps, longitude and a flat page
Al-Biruni also worked on a hard problem: showing a round Earth on a flat page. Before 995 he wrote a study on map projections. In it he explained how to transfer a hemisphere onto a plane.
You deal with the same problem whenever you open a map on your phone and zoom out. A round surface has to be drawn flat, and some distortion cannot be avoided.
Longitude was another task. On 24 May 997 there was a lunar eclipse. Al-Biruni watched it from Kâs. Abu’l-Wafa watched it from Baghdad. By comparing the times each of them recorded, they could work out the longitude difference between the two cities.
How did Al-Biruni measure the Earth?
This is the part most readers come for. Al-Biruni applied his method for finding the Earth’s radius in the 11th century at Nandana, in what is now Pakistan.
The idea works in two steps.
Step 1: find the height of a mountain. You pick two points whose distance apart you know. From each, you measure the angle up to the summit. With those angles and the known distance, trigonometry gives you the mountain’s height.
Step 2: look at the horizon from the top. From the summit, the horizon lies slightly below a level line. That is the dip of the horizon. Al-Biruni measured this angle. Combined with the mountain’s height, it gives the Earth’s radius.
The modern way to write it is:
R = h × cos(θ) / (1 − cos(θ))
Here h is the mountain’s height. The angle θ is the dip of the horizon. R is the Earth’s radius.
Here is an everyday link. Stand on a hill or a high balcony and look out. The farther you climb, the more the edge of the view drops below your eye level. That small drop is the angle Al-Biruni measured.
Once you have the radius, the circumference follows from it. That is why the story is often told as measuring the Earth’s circumference.
Was he the first? Was he exact?
Two points need care.
First, Al-Biruni was not the first person to calculate the Earth’s size. In his own works he recorded measurements from the time of the Abbasid caliph al-Ma’mun. In those, one degree of a meridian was 56⅔ miles.
Second, the accuracy of his result is disputed.
- Andijan State University reports his result as about 6,339.9 km. It notes that this is 16.8 km smaller than the modern comparison value of 6,356.7 km.
- The Paris Observatory dictionary reaches 6,335.725 km with a convenient unit conversion. It says the closeness is a coincidence. It points to atmospheric refraction, uneven ground and the limits of angle measurement.
- A 2019 study by S. Yu. Maslikov concludes that the method could not deliver the high precision attributed to it. It adds that the modern equivalents of the length units he used are uncertain.
So the method is well documented. The claim that his number matched the modern value almost perfectly is the contested part.
Details you won’t find in guidebooks
- At about 17, he calculated the latitude of his hometown from the Sun’s greatest height.
- He wrote on map projections before the age of about 22, since the work predates 995. That is how he approached flattening a hemisphere.
- Longitude in 997 came from two observers watching one eclipse, one in Kâs and one in Baghdad, and comparing their times.
- The famous portrait of him is imagined. It was made for the thousandth anniversary of his birth. It is kept in the Museum of the History of the Peoples of Uzbekistan in Tashkent.
- His birthplace, Kâs, carries his name today as Beruniy.
Al-Biruni’s picture
People search “al-biruni picture” and find a portrait of him. The image in the TDV encyclopedia is an imagined portrait. It was made for the thousandth anniversary of his birth.
Treat it as an artist’s idea of him, not as a likeness.
When did Al-Biruni die?
The date is disputed. The MacTutor biography at the University of St Andrews says he died in Ghazni on 13 December 1048. The TDV encyclopedia gives 453/1061, with a question mark.
Ghazni was where his later life was centered.
FAQ
Where was Al-Biruni born?
He was born in 973 in Kâs, the central town of Khwarazm. The region now lies inside Uzbekistan.
What was Al-Biruni’s full name?
His full name was Abu’l-Rayhan Muhammad ibn Ahmad al-Biruni.
Did Al-Biruni measure the Earth’s circumference?
He applied a method for finding the Earth’s radius at Nandana, in what is now Pakistan. The circumference follows from the radius. He was not the first to estimate the Earth’s size, and scholars disagree about how precise his result really was.
What are Al-Biruni’s most important books?
Key works include al-Athar al-Baqiya (chronology), Tahdid nihayat al-amakin (mathematical geography), Tahqiq ma li’l-Hind (India), al-Qanun al-Mas’udi (astronomy), al-Jamahir (gems and minerals) and al-Saydala fi’l-tibb (pharmacy and medicine).
Is there a real portrait of Al-Biruni?
The portrait usually shown is an imagined picture. It was made for the thousandth anniversary of his birth and is kept in the Museum of the History of the Peoples of Uzbekistan in Tashkent.
Sources
- TDV İslâm Ansiklopedisi — Bîrûnî islamansiklopedisi.org.tr
- University of St Andrews, MacTutor — Al-Biruni mathshistory.st-andrews.ac.uk
- English Wikipedia — Al-Biruni en.wikipedia.org
- Qatar Digital Library, Julio Samsó — Al-Bīrūnī, high point in the development of Islamic astronomy qdl.qa
- Encyclopaedia Iranica — Biruni, Abu Rayhan, Geography iranicaonline.org
- Andijan State University — One Mountain, One Angle adu.uz
- Paris Observatory — Biruni’s method dictionary.obspm.fr
- S. Yu. Maslikov, Geodeziya i Kartografiya (2019) — Как Бируни измерил Землю geocartography.ru
- English Wikipedia — Beruniy en.wikipedia.org
Image: Lunar phases al-Biruni.jpg — Al-Biruni, Public domain
