Ah, yes, the doppler effect. It makes train whistles even more mysterious when the pitch changes. Now, Bill, tell us about the astronomical equivalent of the Doppler effect, red shift!

As for why sound travels further in winter, colder air is denser, and sound travels faster and further the denser it is. That's why I can't learn anything: instructions travel in one ear and out the other at incredible speed, due to skull density!