Object moved VERY slowly then accelerated incredibly fast from a stop, completely silent.

Was with my mother and sister.  In a car almost to our home, my mother stopped the car when she noticed some lights when looking out her driverside window (looking in a southern direction).  There were several lights of various color which looked as if the object was spinning very slowly, and one blinking light in the center on the top.  It could be seen not far above the tree line in the dark moving in a western direction VERY slowly with no change in elevation.  After debating if it was a helicopter or something we rolled down the window and there was complete silence.  If it had been a helicopter, it would have had to be within a 1/4 mile and would have obviously made considerable noise.  Soon it stopped and began to decend straight down even more slowly than it had been moving.  Suddenly it instantly accelerated almost too fast for our eyes to follow it increasing in elevation and heading in a south-eastern direction.  I thought I could still see it, quite some distance off now, but my mother was quite shaken by it and wanted to get my sister and I home.
Witness indicates that the date of the incident is approximate.  PD