I'm not an authority. however, I have an opinion and I can back it up. This opinion has been formed by attempting to sell science fiction in Hollywood for nearly 10 years, having known several people who have successfully sold science fiction in Hollywood for nearly 10 years, and from having written science fiction starting in 8th grade...
...which I think is a good decade or more before a lot of you whippersnappers were born.
So check it. One of the classic tropes of sci fi is that "Star Wars" ain't it. This probably seems like an odd statement on the face of it, but really - Star Wars is a Kurusawa film from 1958 called "Hidden Fortress."
Yeah, there's photon torpedoes and using the Force and all sorts of shit like that, but calling a taxi a "space taxi" does not make it science fiction. "Star Wars" is an epic about secession and rebellion that, for no real reason other than "it looks cool", happens a long time ago in a galaxy far, far away.
The definition of "science fiction" used by Analog Magazine is as follows:
Star Trek: The Wrath of Khan is about a device that remakes entire planets and the cryogenically-suspended madman who wishes to use it for vengeance. It's science fiction. Take away the Genesis Device and you have no plot. Empire Strikes Back? Hoth could be dudes on horseback.
So what the fuck is a "space movie?"
I offer that a "space movie" is one in which the basic plot of the film does not happen without some aspect of it needing to happen in space.
Silent Running: - space greenhouses being taken care of by Bruce Dern and his merry robots. Space Movie.
Planet of the Apes: - Astronaut flashes forward into the future but who gives a fuck? "Astronaut" could just as easily be Rip Van Winkle.
Moon - Lone astronaut trapped on a moon base. It could be an island, really, but we'll give it a bye because hey, at least it almost all happens in space.
Wall-E - the humans are gone, yeah, but where they are isn't particularly space-like.
2001 - please.
Outland - same gray area as Moon. It was literally pitched as "High Noon in space" so using the Star Wars criteria it ain't a space movie. But it all happens in space, so...
Hitchhiker's Guide - happens almost entirely in space, and gets in for the restaurant at the end of the universe alone.
Gravity - same as 2001. Not even worth discussing.
Spaceballs - mmmmm.... you could go either way.
Star Wars - whether or not it's sci fi, it sure as fuck is a "space movie."
Solaris - happens entirely on planets.
Contact - "space" isn't really space, it's interdimensional weirdness.
Event Horizon - totally space movie.
My opinion, anyway. I'll bet I'm the only person here whose livelihood ever depended on winning that fight, though.