milkway

The Milky Way is a barred spiral galaxy that contains our 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. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος (galaxías kýklos, "milky circle"). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.

The Milky Way is a large galaxy, containing 100-400 billion stars. It has a diameter of about 100,000-120,000 light-years and is estimated to be about 13.6 billion years old. The Milky Way consists of a bar-shaped core region surrounded by a disk of gas, dust, and stars. At the center of the Milky Way is a supermassive black hole known as Sagittarius A*. The Milky Way is part of the Local Group, a group of more than 54 galaxies, including the Andromeda Galaxy, which is the Milky Way's largest neighbor. The Milky Way and Andromeda are expected to collide in about 4.5 billion years, merging to form a new galaxy.