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Special relativity is defined in the absence of gravity. For practical applications, it is a suitable model whenever gravity can be neglected. Bringing gravity into play, and assuming the universality of free fall motion, an analogous reasoning as in the previous section applies: there are no global inertial frames. Instead there are ...
For illustration, the long axis of the planet Mercury is defined as the line through its successive positions of perihelion and aphelion. Over time, the long axis of most orbiting bodies rotates gradually, generally no more than a few degrees per complete revolution, because of gravitational perturbations from other bodies, oblateness in the ...
Solving the Kepler problem is essential to calculate the bending of light by gravity and the motion of a planet orbiting its sun. Solutions are also used to describe the motion of binary stars around each other, and estimate their gradual loss of energy through gravitational radiation .
Vesta and Pallas are nonetheless sometimes considered small terrestrial planets anyway by sources preferring a geophysical definition, because they do share similarities to the rocky planets of the inner solar system. [56] The fourth-largest asteroid, Hygiea (radius 216.5 ± 4 km), is icy.
The equivalence between gravitational and inertial effects does not constitute a complete theory of gravity. When it comes to explaining gravity near our own location on the Earth's surface, noting that our reference frame is not in free fall, so that fictitious forces are to be expected, provides a suitable explanation. But a freely falling ...
That is, the individual gravitational forces exerted on a point at radius r 0 by the elements of the mass outside the radius r 0 cancel each other. As a consequence, for example, within a shell of uniform thickness and density there is no net gravitational acceleration anywhere within the hollow sphere.
Gravitational collapse – inward fall of a body due to the influence of its own gravity. Neutron star – type of stellar remnant that can result from the gravitational collapse of a massive star during a Type II, Type Ib or Type Ic supernova event. Compact star – white dwarfs, neutron stars, other exotic dense stars, and black holes.
Because a stationary system also has a well defined rest frame in which its momentum can be considered to be zero, defining the energy of the system also defines its mass. In general relativity, this mass is called the Komar mass of the system. Komar mass can only be defined for stationary systems. Komar mass can also be defined by a flux integral.