Bad Astronomy: Misconceptions and Misuses Revealed, from ...

42 FROM THE EARTH TO THE MOON
red light
blue light
come from that last molecule and not from the direction of the
Sun. These molecules are all over the sky, while the Sun is in one
little part of the sky. Since blue photons can come from any and all
of these molecules, the effect is that it looks like blue photons are
coming from every direction in the sky and not just the Sun.
That’s why the sky looks blue. Those blue photons are converging
down on you from all directions so that it looks to you
like the sky itself is giving off that blue light. The yellow, green,
orange, and red photons from the Sun get scattered much less than
do blue ones, and so they come straight at you from the Sun without
having suffered all those scatterings.
At this point, you might reasonably ask why the sky isn’t violet.
After all, violet light is bent even more, and actually does scat-
SUN
Red photons travel through the Earth’s atmosphere relatively
unimpeded, because of their relatively long wavelengths.
Blue photons, however, with their considerably
shorter wavelengths, bump and careen around as they are
scattered by molecules in the air. By the time they reach
your eye, they appear to be coming from everywhere in
the sky, making it look blue.