As the Earth spin on its axis, the Sun always shines on one side giving us daylight. On the shaded side it night time. As the Earth continues to turn, the shaded side moves into the Sun's light, and the sunlit side turns away from the light. It takes 24 hours for the Earth to make one complete turn on its exis and our clocks are based on this principle. In the 1940s people discovered that the Earth speeds up and slows down a little as it spins. We have now developed atomic clocks that can measure time exactly.
FACT FILE
The Earth's axis is an imaginary line through the centre of the Earth. This is what the Earth spins around. You can think of the axis as being a stick pushed through the middle of an orange.
resources: Tell me why (Chancellor Press)
image 1: http://www.happycow.org.uk/poems/images/night_day_large.jpg
image 2: http://scienceblogs.com/startswithabang/files/2010/06/axial-tilt.jpg
