Wiechert model

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Wiechert models (after its developer Emil Wiechert ) are earth models of two different dense ellipsoids , the calculating realistic balance figures are used for the terrestrial body.

Thereby an inner ellipsoid for the earth's core is set in an outer ellipsoid for the earth's mantle , which has the dimensions of the earth's ellipsoid . The two bodies are arranged coaxially , but do not necessarily have to have the same rotation duration. The two-shell models can be related to the geophysical data on depth and density of the earth's core. In about 2,900 km depth that forms the core-mantle boundary , even after their discoverers Wiechert Gutenberg - discontinuity is called.

The two different density values ​​of the Wiechert model (3-4 g / cm³ for the mantle and about 10 g / cm³ for the core) bring a better approximation to the true earth figure than the easier to calculate, homogeneous Maclaurin ellipsoid with constant density of 5.52 g / cm³. In the middle of the 20th century , Karl Ledersteger calculated a flattening of 1: 230 for the best-adapted Maclaurin ellipsoid, while the true flattening of the earth is only 1: 298.25. On the other hand, Wiechert model series enabled him to more precisely verify the dynamic flattening of the earth derived from the moon's orbit .