Why does the duration time on the plane differ upon going there and returning?

How come the duration time on the airplane can differ so much, depending on whether you're returning from or going to one destination? eg. the duration time from Sydney to LA is 4, 5 hours different than the duration time from LA to Sydney. Why is that?





Is it possible that it has something to do with the way the world turns...eg...if the plane is flying the same direction as the rotation of the Earth...it would take longer to get to the destination...rather than a plane that was flying opposite the direction of the rotation of the Earth?





All suggestions and opinions are welcome, thank you.|||It has to do with the jet streams. Going west the flight is not in a straight line because you would be heading into a strong wind.


The way back is more direct and you usually have a strong tail wind for faster air speed.


Since the Earth turns from west to east then if the Earth's rotation was the reason for the time difference the flight west would be faster, not slower.|||The location of the jet stream is extremely important for airlines. In the United States and Canada, for example, the time needed to fly east across the continent can be decreased by about 30 minutes if an airplane can fly with the jet stream, or increased by more than that amount if it must fly west against it. On longer intercontinental flights, the difference is even greater, it is faster and cheaper (by flying the pressure pattern) or flying eastbound along with the jet stream and flying around the jet stream going west bound, than taking the shorter great circle route between two points.