Sixteen times each day, the sun rises and sets for those living aboard the International Space Station — a rhythm so compressed it becomes biologically meaningless. Unable to rely on nature's oldest timekeeper, astronauts have turned to engineering: a shared clock, color-shifting lights, and carefully managed darkness to construct a single, coherent human day inside a vessel that offers none. It is a quiet reminder that time, for all its apparent constancy, has always been something we interpret — and now, increasingly, something we must build.