One of the real celestial treats through any size telescope is the giant planet Jupiter. Even a 2-inch scope will let you view its main markings and four largest moons. By watching the moons change their positions night after night, you can experience “real-time” astronomy. That would be a good start. If, however, you want to go deeper into Jupiter observations, I recommend Jupiter and How to Observe It by John W. McAnally (Springer, 2008). Even before...