Bright blue sphere emanating light appeared to move south and east across horizon.

Sometime in July of either 1974 or 1975, three observers were sitting at a stop sign on McIntrye at 32nd Avenue in Golden.  The car was facing south.  It was a clear day with no clouds and no rain coming from the west.  
An object appeared in the horizon from the west and moved rapidly across the sky toward the east and south.  The object briefly hesitated about 3/4 way across the horizon and appeared to move more southward.  
The object was a bright blue sphere that appeared almost transparent but also seemed to emanate light.  By size comparison, the object appeared to be the size of a full, harvest moon.  It is very difficult to determine the distance from the car to the object, but estimates are about 3 miles.  
The observers were a male professional bank auditor; a female college student working for an environmental consulting firm and a professional chemist and quality auditor.  
The female student reported this incident at her workplace and discussed it with the firm's meteorologist.  It was the meteorologists opinion that the object was a plasma ball or ball lightening.  
The female thought this not to be likely as the object appeared to be quite perfect and manufactured rather than a spontaneous natural occurrence.  
My interest in reporting this sighting is to find out if there are any other individuals who witnessed this event.
Witness indicates that the date of the incident is approximate.  PD