Two Planets and Two Moons

Yes, this is a composite of three different images. They were all taken on the same night, with the same camera and telescope and so all are at the same image scale. The North Western limb of our own Moon highlights the crater J. Herschell and its surroundings. Jupiter and Saturn are were also putting on a nice show the night of August 19th, with Jupiter being at opposition. But, look closely, there is another Moon. That moon or natural satellite of Jupiter is an indistinct white dot against the bright planet, but a black dot is clearly visible, being the shadow of IO falling on the planets cloud tops.