تويت
Al-Biruni: A Pioneer in Measuring the Earth's Size
Nearly a millennium ago, the Persian polymath Al-Biruni achieved an extraordinary feat by calculating the Earth's circumference with an accuracy remarkably close to modern measurements. His estimate, made in the 11th century, was within 0.3% of the current accepted value—a testament to his profound understanding of mathematics and astronomy. Al-Biruni’s Life and Contributions
Born in 973 and living until 1048, Al-Biruni was a scholar whose expertise spanned numerous fields, including astronomy, geography, mathematics, physics, and history. Among his many accomplishments, his method for determining the Earth's size stands out as a groundbreaking achievement in the history of science. Methodology Behind the Measurement
In 1030, Al-Biruni employed trigonometric principles to estimate the Earth’s circumference. His calculations relied on the observation that the Earth's curvature causes the horizon to appear at a lower angle when viewed from an elevated position, such as a mountaintop. By carefully measuring the angle between the horizon and a vertical line at two separate locations, he derived the Earth’s radius. From this, he calculated the circumference to be approximately 6,339.6 kilometers—astonishingly close to the modern value of 6,378.1 kilometers. Comparison with Later Measurements
Al-Biruni’s method remained one of the most accurate until the 17th century, when Jean Picard, a French astronomer, refined the measurement using advanced tools and techniques. Al-Biruni’s work, however, laid the foundation for future explorations of geodesy and astronomical measurement.
Eratosthenes’ Groundbreaking Experiment
Centuries before Al-Biruni, the Greek mathematician Eratosthenes devised another ingenious method for measuring the Earth's circumference. His approach combined simple geometry with careful observations of sunlight and shadows. The Principle of the Method
Eratosthenes noted that at noon on the summer solstice in Syene (modern-day Aswan, Egypt), the Sun was directly overhead, casting no shadows. Simultaneously, in Alexandria—located north of Syene—vertical objects did cast shadows. By measuring the angle of these shadows, which he found to be about 7.2 degrees, Eratosthenes concluded that the arc between the two cities represented 1/50th of a full circle.
Knowing the distance between Syene and Alexandria to be approximately 5,000 stadia (where a stadion is roughly 185 meters), he multiplied this distance by 50 to estimate the Earth’s circumference. Using modern units, this calculation translates to about 46,250 kilometers, compared to the actual value of approximately 40,075 kilometers. The discrepancy likely arose from variations in the exact length of the stadion and measurement limitations of the time.
A Hypothetical Flat Earth Perspective
Eratosthenes’ observations have been used to challenge flat Earth theories. If the Earth were flat, the observed differences in shadow angles would require a much closer and smaller Sun than proposed by the heliocentric model. Using the measured 7.2-degree angle and the 800-kilometer distance between Syene and Alexandria, basic trigonometry places the Sun at an altitude of approximately 100 kilometers. Implications of a "Flat Earth" Sun
To match the observed angular diameter of 0.5 degrees, the Sun would need a diameter of about 873 meters. However, sustaining the observed solar radiation levels under these conditions would be impossible with current scientific understanding. The process of nuclear fusion, which powers the Sun, requires immense mass and gravitational forces—conditions incompatible with such a small celestial body.
Nearly a millennium ago, the Persian polymath Al-Biruni achieved an extraordinary feat by calculating the Earth's circumference with an accuracy remarkably close to modern measurements. His estimate, made in the 11th century, was within 0.3% of the current accepted value—a testament to his profound understanding of mathematics and astronomy. Al-Biruni’s Life and Contributions
Born in 973 and living until 1048, Al-Biruni was a scholar whose expertise spanned numerous fields, including astronomy, geography, mathematics, physics, and history. Among his many accomplishments, his method for determining the Earth's size stands out as a groundbreaking achievement in the history of science. Methodology Behind the Measurement
In 1030, Al-Biruni employed trigonometric principles to estimate the Earth’s circumference. His calculations relied on the observation that the Earth's curvature causes the horizon to appear at a lower angle when viewed from an elevated position, such as a mountaintop. By carefully measuring the angle between the horizon and a vertical line at two separate locations, he derived the Earth’s radius. From this, he calculated the circumference to be approximately 6,339.6 kilometers—astonishingly close to the modern value of 6,378.1 kilometers. Comparison with Later Measurements
Al-Biruni’s method remained one of the most accurate until the 17th century, when Jean Picard, a French astronomer, refined the measurement using advanced tools and techniques. Al-Biruni’s work, however, laid the foundation for future explorations of geodesy and astronomical measurement.
Eratosthenes’ Groundbreaking Experiment
Centuries before Al-Biruni, the Greek mathematician Eratosthenes devised another ingenious method for measuring the Earth's circumference. His approach combined simple geometry with careful observations of sunlight and shadows. The Principle of the Method
Eratosthenes noted that at noon on the summer solstice in Syene (modern-day Aswan, Egypt), the Sun was directly overhead, casting no shadows. Simultaneously, in Alexandria—located north of Syene—vertical objects did cast shadows. By measuring the angle of these shadows, which he found to be about 7.2 degrees, Eratosthenes concluded that the arc between the two cities represented 1/50th of a full circle.
Knowing the distance between Syene and Alexandria to be approximately 5,000 stadia (where a stadion is roughly 185 meters), he multiplied this distance by 50 to estimate the Earth’s circumference. Using modern units, this calculation translates to about 46,250 kilometers, compared to the actual value of approximately 40,075 kilometers. The discrepancy likely arose from variations in the exact length of the stadion and measurement limitations of the time.
A Hypothetical Flat Earth Perspective
Eratosthenes’ observations have been used to challenge flat Earth theories. If the Earth were flat, the observed differences in shadow angles would require a much closer and smaller Sun than proposed by the heliocentric model. Using the measured 7.2-degree angle and the 800-kilometer distance between Syene and Alexandria, basic trigonometry places the Sun at an altitude of approximately 100 kilometers. Implications of a "Flat Earth" Sun
To match the observed angular diameter of 0.5 degrees, the Sun would need a diameter of about 873 meters. However, sustaining the observed solar radiation levels under these conditions would be impossible with current scientific understanding. The process of nuclear fusion, which powers the Sun, requires immense mass and gravitational forces—conditions incompatible with such a small celestial body.