Science fiction and fantasy seem to be divided by a pretty definitive line. Science fiction deals in advanced technology that either doesn’t exist yet, such as interplanetary travel on massive levels, or seems to be completely impossible given what we currently understand about science, like Stargates. We suspend our disbelief and for a brief period of time allow for the possibility of the seemingly impossible. Fantasy also requires our suspension of disbelief for another seemingly impossible matter, one that is generally more fantastical that scientific. On top of that, magic is normally an unexplainable construct within a universe, and its existence is usually simply accepted without any kind of reasoning as to why it’s there. That tends to be the purpose of the fantastical. We suspend our disbelief for it, and though we like to learn how it works, we don’t need its existence defined.
This distinction, however, is not always clear cut, and it has resulted in some debate over which category Star Wars falls into. On the one hand, though it takes place “a long time ago”, the setting is still a futuristic society with advanced technology and space travel. On the other hand, the story still utilizes some fantastical elements in how it presents its technology—lightsabers, the Death Star, etc.
But probably most fantastical is the Force. Because of this, I would classify Star Wars as science fantasy, since it has elements of both. I mean, let’s face it; the Force is essentially just magic.