Periapsis angular speed
= Periapsis angular speed
{title2=$\dot\theta_{\rm peri}$}
The <specific angular momentum> of an elliptic <Kepler orbit> is $h=\sqrt{\mu a(1-e^2)}$. At <periapsis>, $r=a(1-e)$, so
$$
\dot\theta_{\rm peri}=\frac h{r^2}=n\frac{\sqrt{1+e}}{(1-e)^{3/2}}.
$$
The <mean motion> understates instantaneous angular speed near <periapsis>. A particle in an <exterior mean-motion resonance> can briefly overtake the planet in angle despite completing full orbits more slowly.