Originally Posted by baddog

Time Zones

What Are They & Why Do We Need Them?

We measure the day by saying that the sun is at it's highest point at 12 o'clock, midday. Because the earth spins, as it travels around the sun, one half of the earth is in darkness and one half in light, all the time. This brings us to a problem. If it is midday where you are, on the opposite side of the earth, it is dark, so what time is it on the opposite side of the world?

Day and Night
Before time keeping and clocks were invented, people used to know approximately what time it was by watching the sun. If you look out of the window, at different times of the day, you will see that the sun is in a different place each time you look. This is the same everywhere in the world. Once clocks were invented, they simply had to look at a clock to know what time it was.

The earth spins on an imaginary line known as its axis, this movement is known as rotation. While it is rotating on its axis, it is also traveling around the sun, this movement is known as revolution. Although the earth is revolving around the sun, the sunlight only falls on the part of the earth facing the sun. So, the part facing the sun has day and the part away from the sun has night. As the earth rotates, different parts are exposed to the sun, and put in the shade.

How Time Zones Work

Because everyone wants to measure their day with the sun being at its highest point at midday, scientists came up with the idea to divide the earth into different time zones. There are 24 hours in a day, so there are 24 time zones. The time is the same everywhere within one time zone, but different to all the other time zones. When you move from one time zone to the next one, you change your watch by one hour. If you are traveling in an easterly direction you move your watch one hour forwards, if you are moving in a westerly direction you move it one hour backwards.

Example:
# New York is west of London, and they are separated by 5 time zones.
# This means that when it is midday in New York it is 5 pm in London.
# When it is midday in London it is 7 am in New York.

This means that just because it is 9:45 AM wherever you might be, it might be 6:45 AM when you call someone that lives west of you.

Thank you. There will be a test later.