3 Blue/Green spheres sighted by two people in Northern sky, flying quickly in tight formation.

3 spheres of a blue-green color were seen flying, in tight formation, in an arch across the Northern sky.  They appeared suddenly, arched across the sky, and then disappeared just as suddenly.  They did not appear to be flaming, or burning, but rather left a bluish/greenish tinted streak behind them that faded quickly as they moved.  Two of us saw them, and both of us were astonished at their speed, color and appearance.