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rainbow
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_h1 rainbow _p [[Communications_satellites|http://en.wikipedia.org/wiki/Communications_satellite]] in the sky reflect radio signals emitted from the earth allowing the transfert of information. A [[rainbow|http://en.wikipedia.org/wiki/Rainbow]] in the sky is a colour gradation produced by the double refraction in the droplets in the clouds of the light emitted by the sun. _ul Imagine three powerful laser [red, green,blue] closely located and emitting towards a cloud. By switching on or off these lights, a set of 8 colours an be produced : [black,red,gree,blue,yellow,magenta,cyan,white]. _ul Imagine an observer looking at these lights : he would see one of these 8 colours. _ul Imagine any observer who can't see directly these lights but looking at the cloud. He would see a "discrete" rainbow made of a maximum of 3 colours [red, green,blue], depending on the state "switched on/off" of the emitter. But he would have all the information to rebuild every colour in the set of 8 colours. For instance red and green are visible so it gives yellow, and so on ... _p Playing with variation of the light emitters intensity, for instance with 8 states [0,1,2,3,4,5,6,7], and with a little help of light analyzers, it would be possible to transmit information coded on the interval 8^3 = 512 = 2^7. _p So, we could forget satellites and use nothing but clouds.