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A "true circumnavigation" of Earth is defined, in order to account for the shape of Earth, to be about 2.5 times as long, including a crossing of the equator, at about 40,000 km (25,000 mi). [24] On the flat Earth model, the ratios would require the Antarctic Circle to be 2.5 times the length of the circumnavigation, or 2.5 × 2.5 = 6.25 times ...
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). While "radius" normally is a characteristic of perfect spheres, the Earth deviates from spherical by only a third of a percent, sufficiently close to treat it as a sphere in many ...
as the shape of the geoid, the mean sea level of the world ocean; or; as the shape of Earth's land surface as it rises above and falls below the sea. As the science of geodesy measured Earth more accurately, the shape of the geoid was first found not to be a perfect sphere but to approximate an oblate spheroid, a specific type of ellipsoid.
Due to the combined effects of gravity and rotation, the figure of the Earth (and of all planets) is not quite a sphere, but instead is slightly flattened in the direction of its axis of rotation. For that reason, in cartography and geodesy the Earth is often approximated by an oblate spheroid, known as the reference ellipsoid, instead of a sphere.
The sum of the angles of a spherical triangle is not equal to 180°. A sphere is a curved surface, but locally the laws of the flat (planar) Euclidean geometry are good approximations. In a small triangle on the face of the earth, the sum of the angles is only slightly more than 180 degrees. A sphere with a spherical triangle on it.
Earth's western hemisphere showing topography relative to Earth's center instead of to mean sea level, as in common topographic maps. Earth has a rounded shape, through hydrostatic equilibrium, [85] with an average diameter of 12,742 kilometres (7,918 mi), making it the fifth largest planetary sized and largest terrestrial object of the Solar ...
In 2016, astronomers spotted an asteroid about the size of a ferris wheel in an Earth-like orbit around the Sun. Turns out it's actually a chunk of the moon.
The 17th-century Ge zhi cao treatise also used the same terminology to describe the shape of Earth that the Eastern-Han scholar Zhang Heng (78–139 AD) had used to describe the shape of the Sun and Moon (as in, that the former was as round as a crossbow bullet, and the latter was the shape of a ball).