My god, it is full of stars! I think everybody knows this sentence and if not, you should watch probably the best movie from Stanley Kubrick 2001: A Space Odyssey (1968). Anyway, my reaction when I processed this image was the same just like David Bowman, when he was traveling through the star gate created by the monolith orbiting the Jupiter. The reason why there are so many stars in the background is simple. M39 is an open cluster located in not far from constellation Cygnus (Swan). This constellation is lying on the plane of our home galaxy Milky Way, therefore we are now looking through the galactic disk.