Traditional Theatre Structure.

George Lucas structured all 3 of the OT movies like a traditional 3 act play.

ANH
Act 1: Everything on Tatooine, including Mos Esely and meeting Han and Chewie, and jumping into hyperdrive.

Act 2: Aldreaan is destroyed, the Falcon arrives, everything on the Death Star, and ending with Leia admitting that she knows the ship is being tracked.

Act 3: The Falcon arrives on Yavin 4, and the final battle.

ESB
Act 1: All of Hoth, ending with Luke and Artoo heading toward Dagohbah.

Act 2: Starts with the Falcon evading the Star Destroyers, includes all of Luke on Dagohbah, and ends with Yoda declaring "There is another."

Act 3: Beings on Cloud City with Leia worried about C-3PO and Lando.

ROTJ
Act 1: All of Jabba's scenes, ends with the two ships leaving and Luke confirming to R2 that he is going back to Dagohbah.

Act 2: Meeting the Emperor, the Rebel plan, arriving on Endor, meeting the Ewoks, and ending with Luke surrendering to Vader.

Act 3: Begins when the find the back door, and is the entire 3 fronts of the Battle for Endor.