very bright light with huge triangular vapor trail emitting from the bottom of the light sourceabout 15 minutes prior to dusk, first witnessed a dim light in the NW sky at about 45 degrees above the horizon; immediately a tremendous white vapor began emitting from the bottom of the light in a huge triange shapped cloud. The light was the source and became incredibly bright as the vapor continued to grow and expand from the light in a perfect triange. I can't estimate the distance to the object, but 50 miles might be a close guesstimate. The light continued to get brighter and continued to gain in size while emitting this gas vapor - the light then travelled in a vertical direction gaining speed at an incredible rate, the light seemed to veer upward and vaporize while the gas vapor triangular cloud remained, much like a contrail. The vapor disapated at a slow rate, but much faster that the evaporation of a contrail...more like dry ice vapor. Within a few minutes of disapearance of the light, the vapor vanished. No sound was heard.