My Christmas tree will always have large lights on it because of this ornament. This is my favorite ornament on the tree, which is coming down today. I call it a "Whirlygig" because it has a small pinwheel inside that spins when the light underneath it (you have to hang it over a light) heats up. This particular one came off of my Grandfather's and then my Mother's tree, which of course makes it very special.
I think they are really called "spinners." In any case, this one shows its years, but will always be my favorite!