When I listen to "Across the Stars", I get the impression that the piece is derived from "Luke and Leia". It seems to me that John Williams wanted the love theme for Anakin and Padme to be connected musically to the theme for their children. Am I the only one who catches this? Or am I just trying too hard to make a connection that isn't there?
Now Playing: Star Wars Main Title and Ambush On Coruscant
Interesting.... Where exactly do you notice similarities? The only one I can really see is the minor-key dominant chord at the end of the first statement of Luke and Leia's theme. But perhaps that's just because Across the Stars is very grounded in its minor key, and Luke and Leia is primarily major.
Whether or not they are connected (which would make a lot of sense!), some things are pretty clear. Luke and Leia is a 'mash-up' of the two characters' respective themes. It's Luke's melody blended with his sister's lovely harmonies - especially the I-iv-I progressions.
As for Across the Stars, it's an evolution of the love theme from Jane Eyre (1970). It's the same general 'Mi Do La' melody shape that we hear in Across the Stars. (It's also in August Rush, and perhaps Korzeniowski's Romeo & Juliet??)