Angular resolution
= Angular resolution
{title2=$\theta_{\rm res}$}
{wiki}
<Angular resolution> describes the smallest angular separation or structure an observation can distinguish. A physical scale $r$ at distance $D$ subtends approximately $r/D$ radians when $r\ll D$. Resolving a <black-hole sphere of influence> therefore involves distance as well as its physical radius, and useful kinematics also require adequate <surface brightness>.