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The Milky Way is the galaxy that includes the Solar System, with a diameter of 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years ). It is a barred spiral galaxy with a supermassive black hole at its center and many satellite galaxies.
Learn about the Sun and the objects that orbit it, including the eight planets, the nine dwarf planets, and the small bodies such as asteroids, comets, and moons. Explore the formation, evolution, and features of the Solar System and its place in the Milky Way galaxy.
Learn how the Solar System formed from the gravitational collapse of a fragment of a giant molecular cloud about 4.6 billion years ago, and how it has evolved since then. Explore the history, evidence, and challenges of the nebular hypothesis, and the fate of the Sun and its planets.
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]
The Oort cloud is a hypothetical cloud of icy planetesimals surrounding the Sun at distances from 2,000 to 200,000 AU. It is thought to be the source of long-period comets and some short-period comets, and to have formed from the protoplanetary disc and the giant planets.
The nebular hypothesis is the most widely accepted model of planetary formation, based on the idea that the Solar System was formed by the gravitational collapse of a giant molecular cloud. Learn about its history, challenges, and variations, as well as other hypotheses such as the tidal hypothesis and the vortex model.
The geocentric model is a superseded description of the Universe with Earth at the center. It was the dominant view in many ancient civilizations, such as Greece, Rome, and Islam, and was based on observations of the apparent motions of the Sun, Moon, planets, and stars.
A comprehensive overview of astronomy as a scientific field, academic discipline, and hobby, covering its branches, techniques, history, and objects. Learn about the nature, formation, evolution, and properties of celestial bodies and phenomena in the universe.