An Explosion?

Last year sometime and one night I was at my friends. We were in his driveway smoking a cig, and the sky was clear and the stars were out. We were looking at the different constellations, just trying to find Ursa Major, and Ursa Minor and I was explaining to him, how to find the Andromeda Galaxy (which I will blog about in another post be sure to stay tuned) anyway, while we were fascinated with the night sky, this crazy thing happened.
We were both looking in the same spot at this bright star, trying to figure out if it was the brightest in the night sky. It was just above his chimney to the right of it. In that instant, I seen a bright light that seemed to start off as a little dot, then it expanded to the size of any other star out there. It was white when it was starting, but after it reached its final size, it then started to die out, and when it was decreasing in size it got fainter too. When it was fading away it turned from a white light to a bluish green light. I thought it was nothing, and my eyes playing tricks on me, but my friend told me "dude, did you see that". Oh sh*t! We both seen it!
It had to be light years away, as far as any other star out there. It wasn't a meteor because it wasn't in our atmosphere. It was way farther than the distance to the moon.
Maybe it was a huge explosion in space, maybe two celestial objects colliding with one another. Maybe it was a supernova, and at that exact moment I got to see it with my own eyes.
I just wonder if I was the only person(and my friend as well) to see this incident.
Is it possible to see a supernova, it wasn't close enough to destroy the earth if the nova happened so its within reasonable distance. Maybe it was life on another planet and they were doing something with their military weapons. Who knows, but what I do know is this:
I got to see an explosion in space with my very own eyes!
if anyone has seen something in space please reply about it, im interested to know. Maybe someone had a similar incident.