A
phenomenon that causes the
sky to be blue and the
sun to be yellow.
Gaseous
molecules in the
atmosphere contain positively
charged elements in their
nuclei and
negatively charged electrons in their
electron cloud. The
electric bond that exists between these
elements can be crudely
modelled as an electric
dipole.
If an electric dipole is hit by
electromagnetic radiation ( such as
light ) of a
frequency that is
close to the natural frequency of its electric bond it may
absorb the radiation and move to a higher energy state.
After a
short time it may then
decay back to its
original more
stable energy state and re-emit the light it absorbed. The light will be re-emitted in a
random direction except along the
axis of
oscillation. ( This
btw is why sunlight is
polarised in some sections of the sky - you are looking along one of the axes of oscillation for the scattered light)
Thus the overall
effect of this is that light of the
right frequency is scattered away from its
original direction of travel
. It just so happens that for the bonds
present in the molecules that make up our atmosphere the right frequency is that of
blue light.