The earth has been divided into twenty-four time zones of one hour each. Each zone thus covers 15° of longitude.
Why these many zones?
The reason behind this is the longitude and time.
- The best means of measuring time is by the movement of the earth, the moon, and the planets. The sun regularly rises and sets every day.
- When the Prime Meridian of Greenwich has the sun at the highest point in the sky, all the places along this meridian will have mid-day or noon.
- As the earth rotates from west to east, those places east of Greenwich will be ahead of Greenwich time and those to the west will be behind it.
How to calculate?
It can be calculated this way-
The earth rotates 360° in about 24 hours, which means 15° an hour or 1° in four minutes. Thus, when it is noon at Greenwich, the time at 15° east of Greenwich will be 15 × 4 = 60 minutes, i.e., 1 hour ahead of Greenwich time, But at 15° west of Greenwich, the time will be behind Greenwich time by one hour
The local time at the longitude, which generally passes through the middle of the country is deemed to be the standard time in that country. This standard time is used all over the country. With respect to businesses at a global level, there should be compatibility between the standard times of various countries. To facilitate this, the world has been divided into 24 time zones. These time zones have been created with reference to the Prime Meridian itself.