A unidentified erratically flying object spotted at night in the Florida Keys in the late seventies

It was late one night, when my mom, dad, childhood friend and I were making one of hundreds of trips up the Florida Keys From Key West back in the late 70s. It was very very dark, little traffic and the sky was clear with lots of stars. My friend and I decided, out of boredom to watch the sky for shooting stars (meteorites).  We saw an occasional plane or airliner with their blinking lights traveling across the sky. 
At one point I was watching one of these "planes" (no blinking lights) when all of a sudden it took off like a shooting star . So that got my attention.  But it never went out of sight.  Instead it stopped  "shooting" and continued at a regular speed like a plane.  At this point, I called everyone’s attention to it. 
Then it shot across the sky again then stopped  and did it again. It was moving in irregular patterns one way then another. We were all just amazed and could not take our eyes off of it, just watching it zig zag around at different speeds.  It seemed like it went on for such a long time. My dad was having a hard time keeping his eyes on the road and on the object too but he didn’t stop, he just slowed down. We were all trying to guess what the heck it could be because we knew it was not a shooting star or a plane. We do have a lot of military Air Force bases down in the Keys but I don’t even think the stealth bomber was in existence or even being tested at that time. I don’t think there was any aircraft at that time that was capable of this kind of movement. We continued to watch it as its movements seemed to take up the whole sky, when suddenly it stopped and just slowly faded out. It looked as if it went straight out into space at a very very high rate of speed until it was just gone from sight. We still talk about it to this day.
Witness indicates that the date of the event is approximate.  PD