Gravity or gravitation is a natural phenomenon by which all things are brought (or gravitate) towards one another - irrespective of size, i.e. stars, planets, galaxies and even light and sub-atomic particles. Gravity has an infinite range, and it cannot be absorbed, transformed, or shielded against. Gravity is responsible for the formation of structures within the universe (namely by creating spheres of hydrogen, igniting them with enough pressure to form stars and then grouping them together in to galaxies), as without gravity, the universe would be composed only of equally spaced particles. On Earth, gravity is commonly recognized in the form of weight where physical objects are harder to pick-up and carry the 'heavier' they are. Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity, not as a force, but as a consequence of the curvature of spacetime caused by the uneven distribution of mass/energy; and resulting in time dilation, where time lapses more slowly in strong gravitation. However, for most applications, gravity is well approximated by Newton's law of universal gravitation, which postulates that gravity is a force where two bodies of mass are directly drawn to each other according to a mathematical relationship, where the attractive force is proportional to the product of their masses and inversely proportional to the squareof the distance between them. This is considered to occur over an infinite range, such that all bodies (with mass) in the universe are drawn to each other no matter how far they are apart. Gravity is the weakest of the four fundamental interactions of nature. The gravitational attraction is approximately 10−38 times the strength of the strong force (i.e. gravity is 38 orders of magnitude weaker), 10−36 times the strength of the electromagnetic force, and 10−29 times the strength of the weak force. As a consequence, gravity has a negligible influence on the behavior of sub-atomic particles, and plays no role in determining the internal properties of everyday matter (but see quantum gravity). On the other hand, gravity is the dominant force at the macroscopic scale, that is the cause of the formation, shape, and trajectory (orbit) of astronomical bodies, including those of asteroids, comets,planets, stars, and galaxies. It is responsible for causing the Earth and the other planets to orbit the Sun; for causing the Moon to orbit the Earth; for the formation of tides; for natural convection, by which fluid flow occurs under the influence of a density gradient and gravity; for heating the interiors of forming stars and planets to very high temperatures; for solar system, galaxy, stellar formation and evolution; and for various other phenomena observed on Earth and throughout the universe. In pursuit of a theory of everything, the merging of general relativity and quantum mechanics (or quantum field theory) into a more general theory of quantum gravity has become an area of research. Aurora![]() An aurora is a natural light display in the sky, predominantly seen in the high latitude (Arctic and Antarctic) regions.[nb 1] Auroras are produced when the Magnetosphere is sufficiently disturbed by the Solar wind that the trajectories of charged particles in both Solar wind and magnetospheric plasma, mainly in the form of electrons and protons, precipitate them into the upper atmosphere (thermosphere/exosphere), where their energy is lost. The resulting ionization and excitation of atmospheric constituents emits light of varying colour and complexity. The form of the aurora, occurring within bands around both polar regions, is also dependent on the amount of acceleration imparted to the precipitating particles. Precipitating protons generally produce optical emissions as incident hydrogen atoms after gaining electrons from the atmosphere. Proton auroras are usually observed at lower latitudes. [2] Different aspects of an aurora are elaborated in various sections below.
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