Why is the sky blue?

The light that comes from the Sun is white, and space is pitch black. So how does the thin layer of air in between manage to paint the whole sky blue? And why does the same sky turn orange and red towards evening? Children ask this question, but the answer kept scientists busy for centuries.

The journey begins with how light relates to colour: you'll experiment to see that white light is really a mixture of many colours, and how colours combine. Then you'll see why the tiny particles in the air scatter blue light more than the other colours, and why sunlight turns red at sunset, when it has a longer path to travel.

In the last step we turn your gaze from the sky to the Earth itself: how does the angle at which sunlight arrives decide the seasons? By following the path of light, one idea explains both the colour of the sky and the heat of summer.