Why do we have different time zones?
We have time zones because Earth rotates, so the Sun rises and sets at different times in different places. Time zones let noon roughly match when the Sun is highest in the sky.
Earth rotates 360 degrees in 24 hours, or 15 degrees each hour. In theory, this gives 24 time zones, each about 15 degrees of longitude wide. Before time zones, towns kept their own local solar time, so clocks in nearby cities could differ by several minutes.
Railways made this confusing, because train timetables needed consistent times. In 1883, North American railroads adopted standard time zones. In 1884, the International Meridian Conference chose the meridian through Greenwich, England, as the starting point, and Greenwich Mean Time became the world's reference. Today, Coordinated Universal Time, or UTC, is used.
Not perfectly straight
Time zone borders follow countries and regions rather than exact lines. Some countries use half-hour or 45-minute offsets, like India at UTC+5:30 and Nepal at UTC+5:45. China uses one time zone for the whole country, and many places change clocks for daylight saving time.
Did You Know?
The International Date Line, roughly along 180 degrees longitude in the Pacific, is where the calendar date changes by one day.