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As you may know, the earth spins around an imaginary pole called "axis". For every 24hours, the earth make a complete turn(rotation) about its axis. Each rotation is termed "day"
For a better understanding of this, think about shining a flashlight on a globe, one side of the ball gets to receive the light and the other side remains dark. The earth can be likened to that globe and the flashlight-The Sun.. Remember we earlier stated that the earth rotates about its axis, and as we know the Sun does not rotate, but is fixed.. With this design, every part of the earth cannot receive the light from the sun at the same time.
Nevertheless, as your location on Earth rotates into sunlight, you see the Sun rise. On the other hand, when your location rotates out of sunlight, you see the Sun set.
Furthermore, the earth moves about 15° every 60minutes about its axis and in 24 hours it would have completed a rotation of 360°. Scientists then used this method to divide the earth into 24 sections or timezone with each time zone having a longitude width of 15°
The imaginary dividing lines begin at Greenwich, a suburb of London. The time at Greenwich is called Greenwich Mean Time (GMT). A move west from the Greenwich, every 15-degree section or time zone is an hour earlier than GMT, while each time zone to the east is an hour later.
In conclusion,having different time zones mean that no matter your position on the earth, your noon remains the middle of the day , when the sun is at its peak, while midnight is in the middle of night when the sun sets.