The International Date Line How Countries Keep Time

The Earth spins on its axis, so different parts of the world face the Sun at different times. Where it faces the Sun, it’s daytime, and where it turns away, it’s night. So, time is different in different places on Earth.

In today’s fast-paced world, with airplanes quickly taking us from one country to another, managing time zones became important. To organize this, scientists drew an imaginary line on the Earth to help countries set their time.

Earth has 360 longitudes (lines of longitude), but they are not all parallel. The starting point is the longitude passing through the city of Greenwich in England. This is called the Prime Meridian. All countries agreed to count time based on this line.

There are 180 longitudes on each side of the Greenwich line. Earth rotates from west to east, so places in the east see sunrise earlier. Countries set their standard time zones based on how far east or west they are from Greenwich. For example, India’s time is 5 hours and 30 minutes ahead of Greenwich Mean Time (GMT).

When airplanes and ships cross the Greenwich line, they adjust to the local time and date of the country they’re entering.