Physics KS3/GCSE: Why is the sky blue?

Greg Foot discovers why the sky is blue.

He explains that outside the Earth’s atmosphere space looks black, but from the Earth’s surface the sky looks blue. He investigates this effect by launching a weather balloon.

The helium filled balloon rises through the atmosphere reaching a height of twenty thousand metres, filming as the colour changes from blue to black. The balloon also collects data concerning atmospheric pressure and temperature. Greg then demonstrates that the graphs for sky colour and atmospheric pressure are a very close match.

He finishes by explaining that the sunlight is scattered by the Earth’s atmosphere and that this effect increases as the atmosphere gets denser near the Earth’s surface. This makes the sky look blue.

Teacher Notes

This short film could be used as an introduction to the composition of the atmosphere.

This could be extended with practical work on the proportion of oxygen in the atmosphere and research into the other components of the atmosphere.

Curriculum Notes

These short films will be relevant for teaching physics and chemistry at both KS3 and KS4 in England, Wales and Northern Ireland and National 4/5 in Scotland.

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