Center Pivot Irrigation

The Real Crop Circles

If you have been in a plane over a large agricultural hub you may have casually glanced out of your window. And then you may have performed a very, very quick double take. What on earth are those circular shapes below?
They are not the alien crop circles of infamy that's for sure - in fact whole fields seem to be circular in shape. There are way too many of them, too, to have been done as some sort of practical joke. So, what are they? Welcome to the world of center pivot irrigation.