Photon count inside a relativistic beaming cone
= Photon count inside a relativistic beaming cone
{title2=$\cos\theta_{1/2}=\beta$}
For isotropic photon emission in a source rest frame, aberration maps its forward hemisphere into a laboratory cone of half-angle $\arccos\beta$. The cone contains half the emitted photons. Direction-dependent Doppler energies mean that this count statement is not an identical half-power statement.