Milky Way Galaxy, large spiral system consisting of several billion stars, one of which is the Sun. It takes its name from the Milky Way, the irregular luminous band of stars and gas clouds that stretches across the sky as seen from Earth. Although Earth lies well within the Milky Way Galaxy (sometimes simply called the Galaxy), astronomers do not have as complete an understanding of its nature as they do of some external star systems. A thick layer of interstellar dust obscures much of the Galaxy from scrutiny by optical telescopes, and astronomers can determine its large-scale structure only with the aid of radio and infrared telescopes, which can detect the forms of radiation that penetrate the obscuring matter.
This article discusses the structure, properties, and component parts of the Milky Way Galaxy. For a full-length discussion of the cosmic universe of which the Galaxy is only a small part, see cosmos. For the star system within the Galaxy that is the home of Earth, see solar system.