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Posidonius calculated the Earth's circumference by reference to the position of the star Canopus.As explained by Cleomedes, Posidonius observed Canopus on but never above the horizon at Rhodes, while at Alexandria he saw it ascend as far as 7 + 1 ⁄ 2 degrees above the horizon (the meridian arc between the latitude of the two locales is actually 5 degrees 14 minutes).
Eratosthenes (c. 276 – c. 194/195 BC), a Greek mathematician who calculated the circumference of the Earth and also the distance from the Earth to the Sun. Hipparchus (c. 190 – c. 120 BC), a Greek mathematician who measured the radii of the Sun and the Moon as well as their distances from the Earth. On the Sizes and Distances
With a stade of 185 m (607 ft), 804,000,000 stadia is 149,000,000 km (93,000,000 mi), approximately the distance from the Earth to the Sun. Eratosthenes also calculated the Sun's diameter. According to Macrobius, Eratosthenes made the diameter of the Sun to be about 27 times that of the Earth. [18] The actual figure is approximately 109 times. [27]
Posidonius's method for calculating the circumference of the Earth, relied on the altitude of the star Canopus. Posidonius was informed in his approach to finding the Earth's circumference by Eratosthenes, who a century earlier arrived at a figure of 252,000 stadia; both men's figures for the Earth's circumference were uncannily accurate.
Eratosthenes (c. 276 – c. 194/195 BC), a Greek mathematician who calculated the circumference of the Earth and also the distance from the Earth to the Sun. Greek mathematics; Hipparchus (c. 190 – c. 120 BC) Posidonius (c. 135 – c. 51 BC), a Greek astronomer and mathematician who calculated the circumference of the Earth.
Eratosthenes (c. 276 – c. 194/195 BC), a Greek mathematician who calculated the circumference of the Earth and also the distance from the Earth to the Sun. Hipparchus (c. 190 – c. 120 BC), a Greek mathematician who measured the radii of the Sun and the Moon as well as their distances from the Earth.
In 2022, he completed an iconic lifetime goal of swimming a distance equivalent to the Earth's circumference. For context, that's about 1.75 million lengths in a 25-yard pool.
The figure Alfraganus used based on these measurements was 56 2/3 miles, giving an Earth circumference of 20,400 miles (32,830 km). [58] 66 2 ⁄ 3 miles results in a calculated planetary circumference of 24,000 miles (39,000 km). [59] [60]