I saw a triangular 'star' formation with fourth moving 'star'.

When I was about 16 years old I went deer hunting with my dad, and we spent the night in his van.  It was a bit chilly, and as I was trying to fall asleep 
I was looking out the back window at the stars.  I saw something peculiar, three 'stars' that were equi-distant apart in a triangle.  A fourth 'star' of the same brightness emerged from the bottom right corner of the triangle and made a slow straight procession to the top 'star' of the triangle and disappeared into it.  
There was a pause of perhaps 6 seconds, then the star re-emerged and moved to the bottom left star of the triangle.  Nothing further happened, and the whole experience is somewhat unremarkable, but I think in retrospect, if indeed I was looking at a stationary craft, perhaps the fourth star was part of a light array on the trailing edge of the craft.  
The formation was stationary, more-or-less directly overhead, and probably a good distance out.  I could not initially make sense of the experience because I was thinking in terms of the moving object being a craft itself, a satellite or plane, but could not reconcile the eccentric stop-and-go movement, or precise relative movement to the other 'stars'.
Witness indicates that the date of the event is approximate.  PD