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.

Answer this question: what is the rotation curve of a spiral galaxy? Let's think fast. Stream of consciousness:
To answer the above question, the relevant sentence is: 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. So the final answer is a plot of the orbital speeds of visible stars or gas in that galaxy versus their radial distance from that galaxy 's centre.