Round saucer disk flying erratic and a high speed.

My mother and I were at the roof top of our building trying to watch the fireworks. We could not see anything because our building was not tall enough to see the show. Then, I looked to the sky northwest direction and saw the shining round saucer, it was moving fast, compering with a regular airplane. I asked to my mother if she was watching at the same object on the sky and her got excited because the object was moving erratic and very shining. It was hard to ignore it.