= Half-angle boost aberration of a null spinor
{title2=$\tan(\theta'/2)=e^{-\kappa}\tan(\theta/2)$}
The <spinor> boost $\operatorname{diag}(e^{\kappa/2},e^{-\kappa/2})$ changes the component-magnitude ratio by $e^{-\kappa}$. The associated active positive-$z$ <Lorentz boost> therefore changes the polar half-angle as displayed and leaves <azimuth> unchanged. Its null-vector <time> scale changes by $\cosh\kappa+\sinh\kappa\cos\theta$, which must be retained separately when normalizing a <spinor> to encode direction.
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