A high voltage transformer is connected to two vertical electrodes that are nearer at the bottom, and farther apart at the top. When the transformer is energized, the higher electric field where the electodes are nearer causes the air to break down and an arc develops. The heat of the arc causes an up draft and the spark rises to the wider gap. When the gap is too wide, the spark dies (only works for AC) and starts again at the bottom.
Question?
Would this work on the moon?
Why does this work with AC but not so well with DC?
