The Oort constants A {\displaystyle A} and B {\displaystyle B} are empirically derived parameters that characterize the local rotational properties of our galaxy, the Milky Way, in the following manner: A = 1 2 B = − 1 2 {\displaystyle {\begin{aligned}&A={\frac {1}{2}}\left\\&B=-{\frac {1}{2}}\left\\\end{aligned}}} where V 0 {\displaystyle V_{0}} and R 0 {\displaystyle R_{0}} are the rotational velocity and distance to the Galactic center, respectively, measured at the position of the Sun, and v and r are the velocities and distances at other positions in our part of the galaxy. Wikipedia