Milky Way

== Milky Way== The   Milky Way  is the   galaxy  that contains our   Solar System. [11] [12] [13] [nb 1]   This name derives from its appearance as a dim "milky" glowing band arching across the night sky, in which the naked eye cannot distinguish individual stars. The term "Milky Way" is a translation of the   Classical Latin<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  via lactea<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">, from the <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Hellenistic Greek<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  γαλαξίας κύκλος<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">(pr. <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  galaxías kýklos<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">, "milky circle"). <sup class="reference" id="cite_ref-eo_galaxy_15-0" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[14] <sup class="reference" id="cite_ref-Jankowski_16-0" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[15] <sup class="reference" id="cite_ref-Schiller_17-0" style="color:rgb(0,0,0);font-family:sans-serif;line-height:1em;">[16] <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">The Milky Way appears like a band because it is a disk-shaped structure being viewed from inside. The fact that this faint band of light is made up of stars was proven in 1610 when <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Galileo Galilei<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">used his telescope to resolve it into individual stars. In the 1920s, observations by astronomer <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  Edwin Hubble<span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">  <span style="color:rgb(0,0,0);font-family:sans-serif;line-height:19.1875px;">showed that the Milky Way is just one of many galaxies.

<p style="margin-top:0.4em;margin-bottom:0.5em;line-height:19.1875px;color:rgb(0,0,0);font-family:sans-serif;">The Milky Way is a barred spiral galaxy 100,000–120,000 light-years in diameter containing 200–400 billion stars. It may contain at least as manyplanets.<sup class="reference" id="cite_ref-Nature-20120111_18-0" style="line-height:1em;">[17] <sup class="reference" id="cite_ref-Space-20130102_19-0" style="line-height:1em;">[18]  The Solar System is located within the disk, around two thirds of the way out from the Galactic Center, on the inner edge of a spiral-shaped concentration of gas and dust called the Orion Arm. The stars in the inner ≈10,000 light-years are organized in a bulge and one or more bars. The very center is marked by an intense radio source named Sagittarius A* which is likely to be a supermassive black hole. Stars and gas throughout the Galaxy rotate about the center at approximately the same speed, which contradicts the laws of Keplerian dynamics. This indicates that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation; this mass is known as dark matter.<sup class="reference" id="cite_ref-Koupelis_Kuhn2007_20-0" style="line-height:1em;">[19]  The rotational period is about 200 million years at the position of the Sun.<sup class="reference" id="cite_ref-Faure_8-1" style="line-height:1em;">[8]  The Galaxy as a whole is moving at a velocity of 552 to 630 km per second, depending on the relative frame of reference. It is estimated to be about 13.2 billion years old, nearly as old as the Universe. Surrounded by several smaller satellite galaxies, the Milky Way is part of the Local Group of galaxies, which forms a subcomponent of the Virgo Supercluster.