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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 contexts and justifying the term "the radius of the Earth".
[3] [4] In the 3rd century BC, Hellenistic astronomy established the roughly spherical shape of Earth as a physical fact and calculated the Earth's circumference. This knowledge was gradually adopted throughout the Old World during Late Antiquity and the Middle Ages .
Three spheres, triple spheres, and related terms may refer to any of the following: Architecture ... a 3-sphere, an n-sphere whose surface is three-dimensional;
Direct projection of 3-sphere into 3D space and covered with surface grid, showing structure as stack of 3D spheres (2-spheres) In mathematics, a hypersphere or 3-sphere is a 4-dimensional analogue of a sphere, and is the 3-dimensional n-sphere. In 4-dimensional Euclidean space, it is the set of points equidistant from a fixed central point.
Earth science or geoscience includes all fields of natural science related to the planet Earth. [1] This is a branch of science dealing with the physical, chemical, and biological complex constitutions and synergistic linkages of Earth's four spheres: the biosphere , hydrosphere / cryosphere , atmosphere , and geosphere (or lithosphere ).
The four spheres (for which most of the other spheres are a subtype of) are the atmosphere, the biosphere, the hydrosphere and the geosphere. Earth's ecosphere lies it self within the heliosphere (the Sun's astrosphere). [4] Listed roughly from outermost to innermost the named spheres of the Earth are:
On a flat Earth, the aircraft would have travelled along three sides of a square, and arrive at a spot about 10,000 kilometres (6,200 mi) from where it started. But because Earth is spherical, in reality it will have travelled along three sides of a triangle, and arrive back very close to its starting point.
Earth's location in the Universe. Universe – all of time and space and its contents.. Observable universe – spherical region of the Universe comprising all matter that may be observed from Earth at the present time, because light and other signals from these objects have had time to reach Earth since the beginning of the cosmological expansion.