Don’t capitalize planet (it’s a common noun, not a proper name) or clockwise (it’s an adjective, for cryin’ out loud!).
The creator of this example ignored the existence of any extrasolar planets that may or may not also rotate clockwise, but… Yeah. Not my job to remedy anyone’s scientific ignorance, as I’ve been told a time or two. I’m just the guy with the red pen, and I should shut up about science and history and all those other things I’m not supposed to know about. *shakes head* If you want to make this sentence more accurate, though, you can just add in the solar system: Venus is the only planet in the solar system that rotates clockwise.