= Deflection angle
{title2=$\delta$}
For a <trajectory> with incoming and outgoing straight <asymptotes>, the deflection angle is the <angle> between its limiting incoming and outgoing <velocity> directions. For an attractive <hyperbolic orbit> of <eccentricity> $e$ and <impact parameter> $d$, $\sin(\delta/2)=1/e$ and $\tan(\delta/2)=GM/(dv^2)$, where $v$ is the incoming <speed> at infinity. The incoming <velocity> points opposite to the incoming radial direction; ignoring that reversal gives the wrong <angle>.
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