Star Wars celebrates the 30th anniversary of Star Wars: Return of the Jedi, and to commemorate this, Star Wars historian J.W. Rinzler has created another coffee-table book, and included never-revealed secrets about the making of the film.

Here are the top 10 things you probably didn't know about Star Wars: Return of the Jedi.

1. George Lucas told Lawrence Kasdan that anyone can use the Force.

Lucas told Kasdan during a marathon story conference that it's just like doing yoga. Or karate. "If you want to take the time to do it, you can do it." It just takes practice and concentration. Lucas also clarified that a "Jedi Master" like Yoda is different from a "Jedi Knight," because "he's a teacher, not a real Jedi." Yoda is like a Guru, who "doesn't go out and fight anybody." And Yoda wouldn't be any good in a fight, against someone like Darth Vader. Kasdan responded: "I understand what you're saying, but I can't believe it; I am in shock."

2. George Lucas wanted to create a really dark ending.

Lucas pitched a really dark ending, where Vader sacrifices himself to take out the Emperor, and then Luke helps Vader take off his famous helmet... and PUTS IT ON HIMSELF! In the transcript of the story session with Lucas and Kasdan, Lucas says "Luke takes his mask off. The mask is the very last thing — and then Luke puts it on and says, 'Now I am Vader.' Whoa! The ultimate twist! 'Now I will go and kill the [Rebel] fleet and I will rule the universe.'" Kasdan immediately responded, "That's what I think should happen" — but Lucas didn't actually want to go that dark because "this is for kids."

Mark Hamill is filmed during Luke's moment of choice: Will he commit patricide or become a true Jedi and show compassion for his father

3. Boba Fett was rumored to be Luke Skywalker's mother.

This development would have made the Star Wars prequels so different. But this was just one of the bizarre fan rumors that the Star Wars Fan Club collected at the time and shared with the cast and crew. One fan rumor that Mark Hamill really liked: Han Solo and Darth Vader were somehow "fused," so that Luke couldn't kill Vader without also killing Han.

4. David Prowse was not told about the fate of Darth Vader.

David Prowse was the body of Darth Vader, and James Earl was the voice. (Jones even joked that if Prowse won an Oscar, he'd want to stand in the wings and voice over his acceptance speech.) Prowse became notorious for leaking plot details during the production of Empire Strikes Back, so Lucas started giving Prowse fake dialogue (which confused the other actors sometimes.) Prowse felt slighted for his contributions to Darth Vader — when he heard rumors they were going to unmask Darth Vader and reveal another actor's face, he couldn't believe it. "They wouldn't do such a dirty deed to me," Prowse is quoted as saying. "They wouldn't put another actor in the suit, and when my big moment arrived, unmask somebody else." He also couldn't believe they would kill off Vader.

5. Yoda and Obi-Wan were going to come back to life.

Lucas toyed with this ending for a long time: Luke's mentors emerge from the "Netherworld" and join Luke in the land of the living, for the final celebration. In several script drafts, when Luke Skywalker confronts Darth Vader and the Emperor, Obi-Wan and Yoda are there, coaching Luke and taunting the Emperor.

There was even a draft that made a plot point that Obi-Wan was at a critical moment where he needed to return to physical existence, or else he'd be pulled back into the Force and lose his identity — and maybe Obi-Wan's Force ghost was keeping the Emperor from exerting his full powers. Lucas wanted to explore the idea that Obi-Wan's ghost was doing something important, given the line in the first movie about Obi-Wan returning more powerful than Vader could imagine.

Also, actor Alec Guinness was hesitant to return for a third installation if he was just going to be standing on a greenscreen and giving more expository dialogue. In one script draft, Obi-Wan gives a long, miserable speech to Luke about how everything that had gone wrong was Obi-Wan's fault, and it's up to Luke to fix Obi-Wan's mess. (And in that speech, Obi-Wan reveals that Uncle Owen was Obi-Wan's brother.)

Carrie Fisher (Princess Leia) and Mark Hamill (Luke Skywalker) on location in California's Buttercup Valley aboard Jabba's barge, April 1982.

6. Luke puts Han into bondage in an early script draft.

George Lucas initially didn't think that Han Solo would be in Return of the Jedi at all — actor Harrison Ford was only contracted for the first two movies, unlike the rest of the main cast. But then Lucas thought maybe they would negotiate a new deal that would allow Han Solo to be defrosted at the very end of the movie and make a brief appearance. Even when Ford was signed up to be in the film, though, early script drafts found ways to get him out of the way — like, in one version, Leia is leading a Rebel attack on a cannon, and Han Solo wants to stop her because it's suicide. So Luke uses the Force to manacle Solo to the Millennium Falcon controls, and keeps "the chained-up Solo" there for a good long while. (That counts as "bondage" if this does.) And while it's true that Harrison Ford pushed for Han Solo to die in the third movie, Lucas never even considered doing it.

7. Richard Marquand wanted a famous actor to be the unmasked Vader.

Marquand originally wanted to remove Vader's helmet to reveal the deformed visage of a famous British stage actor, like Laurence Olivier or John Gielgud, instead of revealing actor Sebastian Shaw. But then Lucas worried that the reveal of a known actor would distract people who "wouldn't take it seriously." So Marquand looked for an actor who is "just a person," with an unremarkable face. Also, Ian McDiarmid almost didn't get to play the Emperor — they were deciding between McDiarmid, who was a young man and thus could handle romping around in all that makeup for hours, and Alan Webb, who was authentically elderly. They actually chose Alan Webb, but he became ill soon afterwards. So McDiarmid got the part, and was young enough to be able to play the role again in the prequels.

George Lucas and Richard Marquand on the Emperor's throne room set at Elstree during principal photography.

8. The Sarlacc had an animatronic tentacle, which Lucas didn't want to use.

The crew built a $50,000 animatronic "arm" for the monstrous underground Sarlacc, which comes out of a hole and grabs a guard, pulling him under. Richard Marquand had approved the use of this contraption, which had wires and a radio remote control. But then Lucas showed up on set and nixed the device, in favor of just wrapping some cloth around the guard's ankle and then pulling it off, while running the camera in reverse.

9. They seriously considered filming Blue Harvest, their fake horror movie.

In the attempt to try and keep fans and journalists from stumbling onto the movie's set, the tagline for Blue Harvest was "Horror Beyond Imagination." During the period when the severe sandstorms made filming impossible for the Sarlacc pit sequence, they were stuck in their trailers — and came up with an actual movie that would fit their title and logline. "We devised a complete movie, which was in fact Blue Harvest," Marquand is quoted as saying. "It would start with Carrie Fisher in her slave girl costume lying asleep in her trailer. We said 'Why not put a ghost in it?' George was going to write a five-page screenplay, I'd shoot it in a couple of days, and it would be 'Horror Beyond Imagination.' The story would have dune buggies coming over the hills invading the trailers, with nothing around them but graves and werewolves. We were seriously going to do it." And Lucas told Hamill that Roger Corman used to shoot a whole movie in two days, so why not?

10. There were going to be two Death Stars, instead of just one.

This would have been one way to raise the stakes. In the original outline, one of the Death Stars is half-completed, and the Rebels blow it up with torpedos after destroying the shield generator. The second one also gets destroyed somehow, around the time Vader betrays the Emperor and jumps into a pool of lava with him - this is in the Imperial City of Abbadon, which got dropped as a location for the big climax.

Harrison Ford in-between setups chatting with George Lucas.