Standing on a small hillside in arvada colorado sunday night around 10pm: it had rained most of the day and the sky was finally clear for stargazing. after 5-10 minutes of looking at the starry sky a bright flash occured ssw of me approximately 60 degrees above horizon. the flash started bright white and faded to a semispherical yellow/white crescent; with a thin spiraling contrail or rocket tail like emmanation shooting away and gaining altitude resebling the smoke trail of a firework: traveling ssw and rapidly gaining altitude untill out of sight. the event was naked eye visible with no sound.