The Rotating Earth

Imagine you are looking south and you see an object, such as a car, moving from east to west.

Now there are two possibilities. Either you are not moving and the car is moving from east to west OR the car isn't moving and you are moving from west to east.

When we look south over the course of a day it appears to move from east to west. We now understand that this is because the Earth is rotating from west to east. On a daily basis at least, the Sun and the stars are virtually fixed and the Earth rotates once a day.

The Sun rises at different times at different longitudes across the face of the Earth. On a particular day in the UK the Sun rises at about 7a.m. and sets at about 7p.m. GMT. In Australia the Sun will rise at about 7p.m. GMT and set at about 7a.m. on the same day. Imagine how confusing this would be. To solve this problem the surface of the Earth has been divided into 24 time zones.

As you move eastward from one time zone to another you must put your watch foreword by one hour.

As you move westward you must put your watch back one hour for each time zone you cross.

pic   NASA

If you travelled on a jet from London to the following destinations what would be the local time when you arrived?

a) A 5 hour flight east to Sydney   b) A 2 hour flight west to New York   c) A 1 hour flight east to Paris

Notice that the lines dividing time zones do not exactly follow lines of longitude. They often follow the boundaries between countries. Why is this?

If you were to go completely around the world from west to east you would have to put your watch foreword 24 times. Going from east to west you would put it back 24 hours. Does this mean you could go round the world in a very fast jet and arrive home before you set off? Well not really.

When you cross the international date line you have to either gain or lose a day depending on which direction you pass it. If you were crossing it from east to west you would gain a day.