Science Fiction covers a very broad genre; from thousands of years into the future to an alternate steampunk past, sci-fi focuses on delivering rational, yet fantastic things to it's fans.
Star Wars is such a thing. We know that things such as lightsabers and Super Star Destroyers are unlikely to ever happen. But, the Star Wars universe has a lot of lore behind it, explanations for it's fantastic concepts and items; a perfect example of an excellently created science fiction universe. It appeals to us because it tries our imagination and our rational thinking, which is something that's hard to do.
Unlike it's counterpart, fantasy, sci-fi tends to explain it's miracles, it's impossible concepts; there are exceptions to this, of course, but I've found this to be true, for the most part.
So that's why I find Science Fiction appealing.