From the fifties, one of the author's first stories I think. Alien ship comes to earth its every so many millennia visit and is shocked at how fast human intelligence and accomplishments developed. They were even more astonished to find that humans had left the planet. Something wrong with the sun I think. Using direction the ground tracking stations are pointing they track the humans down. Last line is to the effect that the aliens have no idea what's in store for them.
I'm thinking this question doesn't break the rules, but if it does I apologize. Thank you.