The Milky Way is a barred spiral galaxy with a D 25 isophotal diameter estimated at 26.8 ± 1.1 kiloparsecs (87,400 ± 3,600 light-years), but only about 1,000 light-years thick at the spiral arms (more at the bulge). Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Doust Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος ( galaxías kýklos), meaning 'milky circle'. The Milky Way 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.
(diameter 25.0 mag/arcsec 2 B-band isophote)
The Galactic Center as seen from Earth's night sky (featuring the telescope's laser guide star).
