Apparent superluminal motion
= Apparent superluminal motion
{title2=$\beta_{\rm app}=\beta\sin\theta/(1-\beta\cos\theta)$}
A moving feature can have inferred transverse speed $\beta_{\rm app}c$ greater than $c$ because its second signal starts closer to the observer. The light-travel delay gives $\beta_{\rm app}=\beta\sin\theta/(1-\beta\cos\theta)$, whose maximum is $\Gamma\beta$ at $\cos\theta=\beta$. No local material or signal speed exceeds $c$.