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Presenter 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 this effect 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.
First broadcast:
11 March 2012

Classroom Ideas

This clip could be used as a discussion stimulus to introduce the idea of how we see colour. This can be extended to use a practical to look at the effect of different filters on the colour that is seen. An alternative use would be as a stimulus for discussion of atmospheric pressure which could be followed by demonstrations of pressure, using apparatus such as Magdeburg spheres.

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