We are all familiar with the wonder of the sun's rays bursting through the clouds. But why does it h

We are all familiar with the wonder of the sun's rays bursting through the clouds. But why does it happen? The sun is 93 million miles away and is enormously bigger than the earth, so the light rays should be parallel when they strike the earth. So how come the light seems to come from a point source behind the clouds? Rather like seeing a candle behind a curtain.

Ron Spencer, Sudbury, UK

• This effect is caused by diffraction. When a standard wave passes through any gap it diffracts on the other side, causing the wave to 'arc'. This causes the spread of the light which is why the rays broaden after passing through gaps in the cloud.

  Ryan Glancy,