<Table> <Tr> <Td> </Td> <Td> This article's lead section may not adequately summarize its contents . To comply with Wikipedia's lead section guidelines, please consider modifying the lead to provide an accessible overview of the article's key points in such a way that it can stand on its own as a concise version of the article . (discuss). (December 2016) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article's lead section may not adequately summarize its contents . To comply with Wikipedia's lead section guidelines, please consider modifying the lead to provide an accessible overview of the article's key points in such a way that it can stand on its own as a concise version of the article . (discuss). (December 2016) </Td> </Tr> <P> The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre . It is typically rendered graphically as a plot, and the data observed from each side of a spiral galaxy are generally asymmetric, so that data from each side are averaged to create the curve . A significant discrepancy exists between the experimental curves observed, and a curve derived from theory . The theory of dark matter was postulated to account for the variance . </P> <P> The rotation curve of a disc galaxy (also called a velocity curve) is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy's centre . The rotation curves of spiral galaxies are asymmetric, so the observational data from each side of a galaxy are generally averaged . Rotation curve asymmetry appears to be normal rather than exceptional . </P>

What is the rotation curve of a spiral galaxy