Wave fronts emanating from a uniformly rotating source point whose linear speed exceeds the speed of light, c. (a) Cross-sections of the wave fronts (the circles in light blue) emanating from a volume element of the current sheet with fixed radial and latitudinal coordinates. This figure is plotted for a source element the radius of whose orbit (the dotted circle) is 2.5 times the radius c/ω of the light cylinder (the green circle). Cross-sections of the two sheets of the envelope of these wave fronts with the plane of the orbit (shown in dark blue) meet at a cusp and wind around the rotation axis, while moving away from it all the way to the far zone. (b) By receiving three wave fronts (the circles in brown, pink, and orange) centred at three distinct retarded positions (I₁, I₂, and I₃) of the source point S, an observer, P, inside the envelope detects three images of S simultaneously (I₁, I₂, and I₃).