Skumanich rotation law
= Skumanich rotation law
{c}
{title2=$\Omega\propto t^{-1/2}$}
If the moment of inertia I changes slowly and <wind-driven magnetic braking of a solar-type star> has torque $-K\Omega^3$, then $\Omega^{-2}(t)=\Omega^{-2}(t_0)+2K(t-t_0)/I$. At sufficiently late times within this unsaturated approximation, rotation scales as $t^{-1/2}$. This empirical main-sequence trend is not a universal law for saturated rapid rotators, changing stellar structure or every magnetic geometry.