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Modified Newtonian dynamics. Modified Newtonian dynamics (MOND) is a theory that proposes a modification of Newton's second law to account for observed properties of galaxies. Its primary motivation is to explain galaxy rotation curves without invoking dark matter, and is one of the most well-known theories of this class.
The Milky Way[ c ] is the galaxy that includes the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye.
Contents. Formation and evolution of the Solar System. There is evidence that the formation of the Solar System began about 4.6 billion years ago with the gravitational collapse of a small part of a giant molecular cloud. [ 1 ] Most of the collapsing mass collected in the center, forming the Sun, while the rest flattened into a protoplanetary ...
The Chamberlin–Moulton planetesimal hypothesis was proposed in 1905 by geologist Thomas Chrowder Chamberlin and astronomer Forest Ray Moulton to describe the formation of the Solar System. It was proposed as a replacement for the Laplacian version of the nebular hypothesis that had prevailed since the 19th century. The hypothesis was based on ...
The Solar System's location in the Milky Way is a factor in the evolutionary history of life on Earth. Spiral arms are home to a far larger concentration of supernovae , gravitational instabilities, and radiation that could disrupt the Solar System, but since Earth stays in the Local Spur and therefore does not pass frequently through spiral ...
Welteislehre. Welteislehre (WEL; "World Ice Theory" or "World Ice Doctrine"), also known as Glazial-Kosmogonie (Glacial Cosmogony), is a discredited cosmological concept proposed by Hanns Hörbiger, an Austrian engineer and inventor. According to his ideas, ice was the basic substance of all cosmic processes, and ice moons, ice planets, and the ...
5th century BC — Democritus proposes that the bright band in the night sky known as the Milky Way might consist of stars. 4th century BC — Aristotle believes the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of the atmosphere, in the region of the world which ...
Galactocentrism. In astronomy, galactocentrism is the theory that the Milky Way Galaxy, home of Earth ' s Solar System, is at or near the center of the Universe. [1][2] Thomas Wright and Immanuel Kant first speculated that fuzzy patches of light called nebulae were actually distant "island universes" consisting of many stellar systems. [3]