Why time zones bend around borders
A time zone is a shared clock, not a strip of Earth measured precisely by longitude. The ideal geometry is simple: Earth turns 360 degrees in about 24 hours, so places 15 degrees apart in longitude differ by roughly one hour in local solar time. But everyday clocks need to work for communities, not just match the Sun’s position.
The clock follows people
If every boundary ran straight along a meridian—the imaginary line joining the poles—nearby towns could end up using different dates or hours simply because they sat on opposite sides of a line. Governments and local authorities instead choose boundaries that keep connected places on the same clock, often aligning them with national borders or regional ties. The result can be a zone that bends, narrows, or extends far from the neat 15-degree pattern.
That choice is practical, but it creates surprises on maps: crossing a border may change the clock even when the journey is short, while traveling a long distance east or west within one country may leave it unchanged. The Sun still moves steadily across the sky; the clock changes where people have decided that a shared time is more useful than strict longitude.
