Someday, I hope to see the real Northern Lights.  Until then, I have to settle for pictures and creating them for myself.  This is great technique to do, especially on winter cards.

Directions:
1.  Using either sponges or sponge daubers and sponge on 3 or 4 different colors.
2.  Sponge black ink around the edges and then around each color.  Continue to sponge on black till you get the look you desire.