Day length is the time from sunrise to sunset — from four hours to twenty-one across the cities Sol knows, by season.

From sunrise to sunset, the upper edge at a sea horizon. At the equator it holds near twelve hours all year; at 60° north it runs from under six hours in December to over eighteen in June; inside the polar circles it reaches zero and twenty-four. Refraction adds a few minutes at both ends.

It changes fastest at the equinoxes and stands still at the solstices; at the equator it barely moves all year.