For a set of very long (essentially infinitely long) charged parallel plates, the electric field between them is constant, and the electric field is given by
E = ΔV/d
ΔV is the potential difference between the plates and d is the distance of their separation.
If d is halved but E stays constant, then by the relationship above, ΔV must also have been halved.
To create the shapes, stars are arranged on a piece of cardboard in the desired configuration. If the stars are placed in a smiley face pattern on the cardboard, for example, they will explode into a smiley face in the sky. In fact, you may see several smiley faces in the sky at one time.
