Why do we have time zones?

When it is noon in Kochi, it is early morning in London and the middle of the night in New York. The Earth is a ball, and the Sun can only shine on half of it at a time.

Before railways, every town set its own clock by the Sun. Noon was whenever the Sun was highest. This was fine until trains began connecting towns whose clocks disagreed by minutes — timetables became impossible.

In 1884, countries agreed to divide the world into 24 time zones, one for each hour of the Earth’s spin, starting from Greenwich in London. Moving east, you add hours; moving west, you subtract.

India uses one time zone, 5 hours 30 minutes ahead of Greenwich. The half hour is unusual, and it means the Sun rises in Arunachal Pradesh almost two hours before it rises in Gujarat.