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Eratosthenes made several important contributions to mathematics and science, and was a friend of Archimedes. Around 255 BC, he invented the armillary sphere. In On the Circular Motions of the Celestial Bodies, [11] Cleomedes credited him with having calculated the Earth's circumference around 240 BC, with high accuracy. [2]
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
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.
On Sizes and Distances (of the Sun and Moon) (Greek: Περὶ μεγεθῶν καὶ ἀποστημάτων [ἡλίου καὶ σελήνης], romanized: Peri megethon kai apostematon) is a text by the ancient Greek astronomer Hipparchus (c. 190 – c. 120 BC) in which approximations are made for the radii of the Sun and the Moon as well as their distances from the Earth.
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).
Examples of applied mathematics around this time include the construction of analogue computers like the Antikythera mechanism, [30] [31] the accurate measurement of the circumference of the Earth by Eratosthenes (276–194 BC), and the mathematical and mechanical works of Heron (c. 10–70 AD). [32]
Greek name Equal to Modern equivalent Description kochliarion κοχλιάριον: 4.5 mL (0.15 US fl oz; 0.16 imp fl oz) spoon chēmē χήμη: 2 kochliaria 9.1 mL (0.31 US fl oz; 0.32 imp fl oz) a measure [7] mystron μύστρον: 2 + 1 ⁄ 2 kochliaria 11.4 mL (0.39 US fl oz; 0.40 imp fl oz) Roman ligula: konchē κόγχη