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A sphere (from Greek σφαῖρα, sphaîra) [1] is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. Formally, a sphere is the set of points that are all at the same distance r from a given point in three-dimensional space. [2]
21 Δεκ 2020 · The ancient Greeks believed the Earth was round and calculated its circumference with remarkable accuracy, while observers inferred our planet’s spherical shape as it cast a curved shadow on the Moon during lunar eclipses.
It was around 500 B.C. that Pythagoras first proposed a spherical Earth, mainly on aesthetic grounds rather than on any physical evidence. Like many Greeks, he believed the sphere was the most perfect shape.
Spherical Earth or Earth's curvature refers to the approximation of the figure of the Earth to a sphere. The concept of a spherical Earth gradually displaced earlier beliefs in a flat Earth during classical antiquity and the Middle Ages.
10 Σεπ 2023 · One notable mis-step was to credit the discovery that the Earth is a sphere to Pythagoras (c. 570–c. 500 BC). Heath’s Aristarchus of Samos: The Copernicus of Antiquity (1913 and still in print) begins with a brief history of astronomy up until Aristarchus’ time in the 3 rd century BC.
17 Μαρ 2024 · The shape of the earth is called the geoid. An ellipsoid is just an approximation, and the geoid deviates from the reference ellipsoid by up to 106 m. A sphere is, in turn, an approximation to the reference ellipsoid. The ellipsoid deviates from the sphere by up to 14 km.
The simplest model for the shape of the entire Earth is a sphere. The Earth's radius is the distance from Earth's center to its surface, about 6,371 km (3,959 mi).
