In the olden days, when televisions were analog and there was only real news, if you stayed up late enough you saw this. Test patterns were created to ensure that everything was working properly in TV land: that nothing had been knocked out of whack, that everything was calibrating just as it had been designed and was functioning at an optimum level. Test patterns operated according to accepted limits of perception. Any required adjustment was made within those parameters.As I drove a delightfully endless highway today, it occurred to me that eclipses are kind of the same thing. They too are designed to test us. If we have veered too far from where we could be (or perhaps should be when functioning at our optimum) they correct us. If we are so out of whack that nobody can make us out, they get to fixing us in an effort to return us to a baseline that is recognised and understood. And if everything is in perfect symmetry, not too much needs to change - and it doesn't.