Circular Cross Sections
[math]\displaystyle{ \vartriangleleft }[/math] [math]\displaystyle{ \triangle }[/math] [math]\displaystyle{ \vartriangleright }[/math]
Circular Conic Section
If the conic is an circle, e=0. This implies
Using the relation
The sector angle will never be perpendicular to the plane of the light cone, so this is not a physical possibility.