Earth is divided into roughly 24 time zones, each one about 15 degrees of longitude wide.

The longer version

A full circle holds 360 degrees, and Earth turns through it in about 24 hours. Dividing one by the other gives 15 degrees per hour, so each time zone spans roughly that slice of longitude. Clocks then step by an hour as you cross each band. The scheme is an approximation of a continuous physical effect.

Real borders rarely follow the maths. Countries bend zone lines to keep a region, an island group or a trading partner on the same clock, so actual zones wander far from neat meridians. Some span enormous widths, and a few places keep offsets that make their local time distinctly odd. The neat arithmetic of the globe gives way to politics on the ground.

Where this entry sits

These facts wander through clocks, calendars, time zones, and the long human effort to measure passing hours. You will find leap years, odd month lengths, ancient sundials, and the reasons modern timekeeping works the way it does. The full list sits on the Time and Calendars page, where every entry is listed in order.