This mesmerizing mind-bender sneaks up and hits you hard. Sam Rockwell, reliably brilliant, is an astronaut finishing up a three-year stint on the moon, mining energy from lunar rock. He wants back on Earth with his wife and daughter. His only contact is GERTY, a robot with the sweet-sinister voice of Kevin Spacey. There’s an accident. A new astronaut appears, looking just like the old one. I’ll say no more. Director Duncan Jones (son of David Bowie), working from a script by Nathan Parker, pulls off sci-fi miracles on a $5 million shoestring. Moon is a potent provocation that relies on ideas instead of computer tricks to stir up excitement.