the discovery

Air. The most transparent and the most colourless of all objects. Is it really so?
The actor, drawing an analogy between the waves of the sea and those of light and narrating about the crew of a small boat or a large vessel shaken by rough waters and by the electrons accelerated by light, explains that, according to the laws of physics, air should not be transparent, but sky-blue. All small particles, smaller than the length of the wave of light, mainly diffuse the blue colour, and they reveal their sky-blue nature when illuminated on a dark background.


The scenario is explained by using a new and spectacular mise en scene. Two identical landscapes, reproducing a kind of animated scenery with mountain chains at different distances, are immersed into two aquariums. The first one is filled in with pure water, and represents a lunar landscape, characterized by the same colours both in the foreground and at the horizon. While the second pool, is filled in with water and glass nanospheres. In water, these transparent particles create density fluctuations similar to those produced by air molecules in the atmosphere. Being remarkably smaller than the wavelength of light, these particles diffuse the blue colour. Thus the scenery looks very similar to the colours of forests and mountains that become bluer in distance.

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Let's have a look at the panorama of a city in autumn. The red and the yellow of the trees on the foreground contrast with the blue of the air at the distance. The air seems bluer in the dark shadow of woods at the horizon, while it disappears in front of white houses and light coloured buildings. It perfectly corresponds with our experience of nature.

In the evening the sunlight reaches us after having crossed the whole atmosphere. During its journey it diffuses blue light, then green, yellow, etc. until just orange and red are left to illuminate the clouds in the sky. Finally, the sky is illuminated from above and it becomes light blue, assuming familiar colours of a blue sky at sunset. In nature, the presence of ozone in the higher part of the atmosphere (which absorbs red and orange) further contributes to the blue colour of the sky.
This experiment demonstrates that the colour of the sky at sunset is not red. Objects illuminated by the sun are red, yellow and orange. But the sky above our heads remains blue.

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