These were black half spheres in a triangular formation

This was years ago but still remains clear. As a boy, during a sunny afternoon with big white clouds in the sky there appeared three  black half spheres in a perfect triangular formation. They came out above the clouds against the blue and hovered a bit, went behind the clouds and came out again. This was all very slow and happened at least twice. There was nothing visible holding these Half spheres together.
Date is approximate.  PD