Why is the Sky Blue?
Page 4

Because the atomic nuclei in the molecules are massive (in atomic scale terms), the alternating forces of ATTRACTION and REPULSION from the passing light waves move the nuclei very little if any at all. The tiny electrons however are jiggled rapidly back and forth . So....

1. Moving Electrons mean a MOVING ELECTRIC CHARGE.

2. A moving electric charge CREATES A MOVING MAGNETIC FIELD....
(remember and so on to infinity on page 2)

Simplified animation of electrons accelerated by passing electromagnetic radiation.

3. Presto!!! - we have:

• ELECTRO-MAGNETIC RADIATION
• GENERATED BY ELECTRONS
• THAT HAVE BEEN DISTURBED BY LIGHT PASSING NEARBY
• AND IS NOW RADIATED BY THE ELECTRONS
• WE CALL THE RADIATED LIGHT

  SCATTERED LIGHT!

4. This is called RAYLEIGH SCATTERING after John William Strutt Rayleigh (Lord Rayleigh).
Sunlight is scattered in all directions in the atmosphere by Oxygen and Nitrogen molecules, which are much smaller than the wavelength of visible light. Because the O₂ and N₂ molecules are small all the electrons experience the same force at the same time making this a fairly straightforward situation. In bigger molecules electrons may be moving in different directions and scattering in much more complex ways.

BUT STEVE! (you exclaim with great anticipation)...

that explains why the sky is lighted....you still have not explained why it is blue!

Because red light has a longer wavelength than blue light (recall that white light from the sun is the sum of Red-Orange-Yellow-Green-Blue-Violet) the electrons are accelerated (jiggled) back and forth faster by blue light than by red light AND THEREFORE more blue light is scattered than red light (It may not be obvious from this but blue light jiggles the electrons faster than red, orange, yellow or green light so they radiate - that is scatter - blue light). As a matter of fact if you look into the mathematics that describes this (I will not do that here) we find that 4.92 times more blue light (wavelength 470 nanometers) is scattered than red light (700 nanometers).

This is what Lord Rayleigh discovered:

HOLD ON NOW STEVE, SOMETHING DOESN'T ADD UP HERE
(you say skeptically with a furrowed brow)...

You just demonstrated that the sky is violet, not blue, because more violet light is scattered than blue. So Mr. know-ti-all why do I see blue and not violet?