A white ball was moving across the sky. It has a tail like a comet. The sun was just below the horison.

Then the light stopped.  It  hung in the air a few seconds.
Then concentric rings of white light eminated from the object.  Like the pattern you see when a stone is dropped into water.
Then it was gone leaving a glowing green cloud that remained for about an houur or so.
The summary contains all the information. 
The sighting was short, and the background was the twilight sky.
Witness indicates that the date of the event is approximate.  PD