point of light ,like on a jet, divided into 2 points with large flash and disappeared over horizon in 12 seconds

I had stopped in the country on the way home from work and was sitting parked in my car enjoying the evening and summer breeze. I noticed what I supposed was a Jet on the horizon in front of me headed due north. I thought I would wait for the jet to pass over head and would then continue home. I watched the jet for about 15 min. untill it was at about the 10 oclock position in the sky when it seemed to explode with a very large burst of light. When my eyes refocused it had become 2 points of light that were moving away from where I last saw the jet. One going east and one going west at equal speeds. Each reached the horizon in about 12 seconds and went out of sight. If a normal jet travels at 500 mph and I watched it for 15 min. how fast was it going to reach the horizon in 12 seconds?
Witness indicates that date of incident is approximate.  PD