Why is the Sky Blue?

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These two tell us that some interaction of light and atmosphere create a blue sky.

THE NATURE OF LIGHT (and a Little History of Science)

Our explanation begins with light. Light is electromagnetic radiation, which is very cool stuff because it can do something nothing else in the universe can do, travel without help from anything.

Waves on a rope you snap are supported by the rope, waves caused by dropping a rock in a pond are supported by the water, waves in the atmosphere caused as air flows over a mountain range are supported by the air molecules, electromagnetic waves need none of this they support themselves.

When an electric charge is disturbed, that is ACCELERATED like snapping a rope, the ELECTRIC charge creates a changing magnetic charge (remember light is ELECTRO-MAGNETIC radiation) and the new changing magnetic charge creates a changing electric charge which creates....(you guessed it) a changing magnetic charge which creates...ho hum...more of the same... and ... more of the same ... and more of the same ...on and on to infinity.

This is how light supports itself. These results are not new Andre Marie Ampere in 1820 demonstrated that an electric current caused (induced) a magnetic field. In the 1830's Michael Faraday reversed that reasoning and showed that magnetism induced an electric field and in 1864 James Clerk Maxwell was able to show (in full mathematical detail) that electromagnetic radiation was a happy marriage between electric and magnetic fields. But incredibly his results were identical to work already completed on light and Maxwell thus proved that light is an electromagnetic wave!

Electric field part of an electromagnetic wave, moving to the right along the black axis.

Small red arrows indicate the direction a positively charged particle atomic nucleus is accelerated when it
encounters the OPPOSITELY CHARGED electric field of light passing nearby. Electrons negatively charged particlesare accelerated in the in the direction indicated by the orange arrows.

Electrical portion of  EM wave


For simplicity only the electric field in a single plane is shown. If looking along the axis the arrows would extend in all directions radially outward
from the axis as in the diagram below. But alas, even with modern software I cannot illustrate it meaningfully in 3 dimensions.
In the situation above the light is said to be polarized.

Electric field looking along the x-axis

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2008 Steven L. Horstmeyer, all rights reserved

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