1. The problem statement, all variables and given/known data A star surrounded by a sphere of dust with a radius R. The star emits a short bright flash of light, it is absorbed and re-emitted by the dust. Someone much further away than R sees the light, first at a point on the shell and then in an expanding ring. A)Show that the rate dr/dt of the ring expanding is given in an appropriate first order approximation by: dr/dt=(speed of light)(cot(theta)) 3. The attempt at a solution I have really know idea how to start this one. I could really use a hint to get started.