is ever true.

But wait-- at some point we must hit on the old definition of a day (the one that the modern second definitions were calibrated to). Like, there is some angle measured from somewhere that is exactly the same for the sun exactly 24 hours apart. Maybe it's the longitude where solar noon is happening or something like that, but there is a real, exactly-24-hour cycle in there where some coordinate of the sun's new position is meaningfully "the same" as what it was 24 hours ago. This *must* be true.