Jupiter is one of the brightest objects in the sky and on a clear night, it is pretty easy to see it's moons.
This is a heavily cropped picture taken using a 500mm lens with a 2x converter. The camera is on a tri-pod for stabilization. A 10 sec. shutter delay with mirror lockup is used to let the camera stabilize before the image is captured. Any movement makes the image blurry. The camera has a APS-C sensor which gives an effective 1500mm focal length. I have to overexpose Jupiter to capture the moons. A free program called Stellarium is used to identify the moons.