= Energy-normalized angular momentum for a Schwarzschild geodesic
{title2=$J=c^2L_\infty/E_\infty$}
For an unbound equatorial <Schwarzschild spacetime> <geodesic>, let $E_\infty$ and $L_\infty$ be its conserved <energy> and <angular momentum> measured relative to infinity. The ratio $J=c^2L_\infty/E_\infty$ has dimensions of area divided by time. For a massive <test particle>, $E_\infty=m c^2\gamma_\infty$ and $L_\infty=m\ell$, so $J=\ell/\gamma_\infty=bv_\infty$, where $\ell$ is <specific angular momentum> and $b$ the <impact parameter>. For a <photon>, $E_\infty=cp_\infty$ and $L_\infty=bp_\infty$, giving $J=bc$ without assigning a finite <Lorentz factor> or a <proper time> to the <photon>. This ratio removes the arbitrary normalization of a null <affine parameter>.
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