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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 ...
To measure the local variation of Earth's topography, geodesy employs an idealized Earth producing a shape called a geoid. Such a geoid shape is gained if the ocean is idealized, covering Earth completely and without any perturbations such as tides and winds.
An Earth ellipsoid or Earth spheroid is a mathematical figure approximating the Earth's form, used as a reference frame for computations in geodesy, astronomy, and the geosciences. Various different ellipsoids have been used as approximations. It is a spheroid (an ellipsoid of revolution) whose minor axis (shorter diameter), which connects the ...
Spherical Earth or Earth's curvature refers to the approximation of the figure of the Earth as a sphere . The earliest documented mention of the concept dates from around the 5th century BC, when it appears in the writings of Greek philosophers. [1] [2] In the 3rd century BC, Hellenistic astronomy established the roughly spherical shape of ...
Size and shape. On the basis of the seismic data, the inner core is estimated to be about 1221 km in radius (2442 km in diameter), [5] which is about 19% of the radius of the Earth and 70% of the radius of the Moon. Its volume is about 7.6 billion cubic km ( 7.6 × 10 m ), which is about (0.69%) of the volume of the whole Earth.
The term geophysics classically refers to solid earth applications: Earth's shape; its gravitational, magnetic fields, and electromagnetic fields ; its internal structure and composition; its dynamics and their surface expression in plate tectonics, the generation of magmas, volcanism and rock formation. [3]
The internal structure of Earth is the layers of the Earth, excluding its atmosphere and hydrosphere. The structure consists of an outer silicate solid crust, a highly viscous asthenosphere and solid mantle, a liquid outer core whose flow generates the Earth's magnetic field, and a solid inner core . Scientific understanding of the internal ...
However, the Earth's actual shape is closer to an oblate ellipsoid. Whether spherical or ellipsoidal, the principles discussed hold without loss of generality. Selecting a model for a shape of the Earth involves choosing between the advantages and disadvantages of a sphere versus an ellipsoid.