Galaxy

A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas dust, and an important but poorly understood component tentatively dubbed dark matter.The name is from the Greek root galaxias [γαλαξίας], literally meaning "milky", a reference to the Milky Way galaxy. Typical galaxies range from dwarfs with as few as ten million (107) stars, up to giants with a hundred trillion (1014) stars, all orbiting the galaxy's center of mass. Galaxies may contain many star systems, star clusters, and various interstellar clouds. The Sun is one of the stars in the Milky Way galaxy; the Solar System includes the Earth and all the other objects that orbit the Sun.