Spiral Arms - Milky Way. Stars and gases at a wide range of distances from the Galactic center orbit at approximately 220 kilometers per second.
The constant rotation speed contradicts the laws of Keplerian dynamics and suggests that much of the mass of the Milky Way does not emit or absorb electromagnetic radiation. This mass has been given the name “dark matter”.[22] The rotational period is about 240 million years at the position of the Sun.[9] The Galaxy as a whole is moving at a velocity of approximately 600 km per second with respect to extragalactic frames of reference. The oldest known star in the Galaxy is at least 13.6 billion years old and thus must have formed shortly after the Big Bang.[6] 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. Appearance[edit] The Milky Way has a relatively low surface brightness.
Carina–Sagittarius Arm (aka Sagittarius Arm or Sagittarius–Carin. Scutum–Centaurus Arm (aka Scutum-Crux Arm) Norma Arm and Outer Arm. Perseus Arm. 3-kpc Arm.