Green flash amongst the stars

We were watching the sky for the Persied meteor shower. Clear sky, no clouds or moon out. We just saw a shooting star and pointed it out to each other. As we were pointing, just to the left of where we were looking we suddenly saw a green flash. For reference, It happened to the left of the Big Dipper. It was circular and small from our perspective, but the size of the bigger stars in the sky. It was like a camera flash. Very quick. There was a pause, then it happened again about 4 seconds later and that was it. No craft, no plane, not a comet, just a small green camera flash in outer space.