Transcript: Maps of star and gas motions reveal the rotation curve of the Milky Way galaxy shown as a plot of orbital speed or circular velocity as a function of distance from the galactic center. In the Milky Way the speed is zero at the center and it rises rapidly to two hundred kilometers per second one kiloparsec out. Then there’s a slight decline and a steady rise to two hundred and twenty-five kilometers per second at the position of the Sun and a subsequent steady rise to two hundred and sixty kilometers per second fifteen kiloparsecs out from the center. Beyond that the motions are difficult to detect. This flat or slowly rising rotation curve is very different from Keplerian orbits which always decline steadily with distance from the center of mass.