A blue, firey ball, about 20 feet wide and 150 feet in the air, flies over head at a slow rate making no sound and lighting up the goun

A slow-moving, firey ball, emitting a soft blue light, passed over a group of five teenagers (myself included) at about 100 feet above the tree line some time in 1990.  This object made no sound, and it was bright enough to light up the ground and cast leaf-shaped shadows on each of our faces as its light passed through the tree branches over head.
It would be hard to estimate size, not knowing the exact altitude of the object, but a guess, based on estimated distance, would be between 10 to 20 feet in diameter.
(Note:  Other strange craft in the area had been seen by several of us prior to this experience, though this was the first time any of us had seen something together.) We were setting up a campsite on a friend's property when this happened, and, to be honest, it scared us, and we elected to move indoors for the night.
Witness indicates that date of sighting is approximate.  PD