The image shows the asteroid Vesta in relation to the planet Jupiter and the four Galilean Moons on August 25. Vesta is west of Jupiter and will move eastward to close the gap with Jupiter. Closest approach to Jupiter will occur on August 29 and August 30.
By September 1, both Jupiter and Vesta have moved eastward. On this night only three Galilean moons are easily seen. Europa is behind the planet and the "last moon" in line is really a star. Vesta has passed by Jupiter and will soon leave the area.