the diameter looks 50m approximation.in the center,looks like black clouds,and something like rainbow around it.i was ready to go home with others at that time.when i was getting up the bus,i heard somebody speak alound"look!,look!".and i found they were looking up the sky.there is the thing i beleive it is an UFO. it is beautiful and mystery.beause my english is poor,i can not tell the thing very clear.but trust me,it is great really.