There were great men who, without modern instruments and computers, accomplished remarkable feats and devised almost accurate measurements of the earth, chemical formulas and mathematical principles on which the edifice of science stands today.

Surprisingly, today NASA takes the radius of the earth with its space planet and the latest technology as 6371 kilometres, which was measured by Abu Rayhan al-Biruni with amazing accuracy about a thousand years ago, which was 6335 kilometres.

Now the question arises: how did Albiruni make this measurement? Before al-Biruni, Ma'mun al-Rashid commissioned two groups of experts to measure the land. These experts travelled north and south across the desert and determined the radius of the earth by repeatedly measuring the angle of the sun at noon.

Al-Biruni also wanted to follow in the footsteps of these experts and do the measurements of the land with more accuracy and precision, but he could not do it due to a lack of capital and the difficult and dangerous work of travelling in the desert.  Alberoni then measured the earth using algebra and geometry and discovered a method that was relatively simple and highly efficient in terms of results.

Al-Biruni chose a hill to measure the angle of the horizon. After choosing a hill, the second step was to measure the height of the hill. For this, Albiruni stood at some distance from the hill and found the first angle (θ 1) of the top of the hill from the ground, then determined the distance d and found the second angle (θ 2), then using these two known angles, the height of the hill was determined by giving the value of the distance d between them in the relevant formula. Al-Biruni used an instrument called an astrolabe to determine angles.

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An astrolabe is an instrument with a large dial and a clock-like knob in the middle. To determine the angle of a hilltop from the ground, Albiruni aligned the two ends of a needle-shaped knob with the top of the hill. When all three are in alignment, one can determine the angle by looking at the degrees written on the dial, just like when aiming a gun by sight.

After finding the height of the hill, Al-Biruni climbed to the top of the hill and with the help of the instrument, he determined the angle of the distant horizon (the place where the sky and the earth meet). It is said that for this measurement, Al-Biruni stayed for a long time in the fort of Nandana (the ruins of the fort of Nandana still exist 22 km from Pind Dadan Khan) and when he thought the air was clear, he climbed the hill to make this measurement.

He repeated this process several times for accurate results. After determining the angle of the horizon, Al-Biruni calculated and found the radius of the earth. Al-Biruni found a total of four values in this process: three angles using an astrolabe, and one distance. Two angles and a distance to find the height of the hill and then the angle to the horizon to get the final result.

Initial Conditions

The famous researcher and scientist Abu Rayhan Muhammad bin Ahmad Al-Biruni, known as Al-Biruni, was born on September 4, 973, in Bayron, a village on the outskirts of Khwarazm, and was called Al-Biruni because of him. Al-Biruni was a contemporary of Bu Ali Sina. When the rule of al-Iraq, the guardians of Al-Biruni, ended in Khwarazm, he travelled to Jurjan, where he completed his great book, "Atar l-Baqiyyah." When the conditions were favourable, Al-Biruni returned to his homeland, where he met the great Abu Ali Sina in court.

Al-Biruni was a lover of natural landscapes from the beginning. Collecting flowers and plants was his hobby; that's why his mother used to call him Abu Rehan. Albiruni's father ran a small business, but due to his sudden death, Albiruni's mother was forced to earn a living by collecting wood from the forest for herself and her son. Al-Biruni used to help his mother with this work.

Al-Biruni mastered Greek and Syriac at the age of 14 and learned much about the plant world from Greek knowledge. His interest in the physical sciences increased. The Greek scholar, before returning to his native Greece, took al-Biruni into the service of the astronomer and mathematician Abu Nasr Mansur Ali (who was a prince of the Khwarizmi dynasty). Abu Nasr built a separate house for Al-Biruni and also fixed a stipend. Abu Nasr taught Al-Biruni astronomy and mathematics every day. Abu Nasr placed Al-Biruni under the tutelage of the famous mathematician and scholar Abd al-Samad.

Al-Biruni's Majesty

Al-Biruni wrote great books in Mathematics, Science, History and Geography, which we still read today. There is also a famous "Kitab-e-Hind," in which Al-Biruni has written about the religious beliefs, history and geographical conditions of the Indian subcontinent with great research.

He wrote more than 150 books and papers on mathematics, science, physics, history, civilization, world religions, geology, chemistry and geography. A crater on the moon is named "Albiruni Crater" in honour of Albiruni's achievements.