Equation to relate voltage to distance of a spark

[professor]

I need to calculate the minimum distance for which a charge of some voltage will jump. Is there any equation that relates distance of a spark jump to voltage (a fairly generalised equation will do, I don't need to worry about strange shapes of the charged bodies that the charge leaps between or anything). Assume that this occurs in a vacuum. (This isn't homework, just part of a side project, and I am stuck because I can't figure out the above sub-problem, which hopefully isn't too difficult).

 

[bassplayer142]

You might want to start with this.

http://en.wikipedia.org/wiki/Dielectric_strength