= High-eccentricity angular-speed crossover
{title2=$r_x=\sqrt{h/n_p}$}
For a nearly radial <Kepler orbit> with <pericentre> $q$, <specific angular momentum> is $h\simeq\sqrt{2GMq}$. Relative to a circular reference orbit of radius $a_p$ and <mean motion> $n_p$, the instantaneous azimuthal rate changes from faster to slower at $r_x=\sqrt{h/n_p}\simeq a_p(2q/a_p)^{1/4}$. In a <rotating reference frame> the polar angle has a turning point at this radius. The <true anomaly> there differs from $\pi$ by approximately $2\sqrt{q/r_x}$.
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