six degrees of light

I'm something of a collector of evocative phrases (see here for another example), and looking at a weather forecast I ran into the phrase "civil twilight." Its official definition is rather mundane (see the link), but the phrase resonates in so many ways. I love it.

And as so often happens, puzzling about one phrase led me to another. I was curious where the "civil" in the phrase comes from, and my best guess has it deriving from this definition: "based on the mean sun and legally recognized by law" (Webster's New Collegiate). "Legally...by law" seems pleonastic - but "mean sun"! The sun, surely, can be cruel - just ask any lazy sunbather who's neglected the SPFs - but mean? Of course, that isn't the sense of "mean" being evoked; rather, a mean sun is "a fictitious sun used for timekeeping that moves uniformly along the celestial equator and maintains a constant rate of apparent motion."

Here in this part of the country, we're quite familiar with the idea of a fictitious sun.