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The Shadow of the Earth in the Smog

Usually, while we are watching a sunset, we're looking west
to enjoy the red and orange colors of the setting Sun. The
longer wavelengths of the Sun's light, the reds and oranges,
tend to come through the atmosphere better than do the blues
which tend to get scattered in all directions, including back
toward the Sun. That's why the setting Sun looks red or
orange. And that's why the sky looks blue. But if, at the
time of the sunset, you look east instead of west, you can
see the blue light that has been scattered from the sunsets
seen by others from farther east. And if you look east just
after the Sun has gone down, you can often see the shadow of
the Earth in the smog.
 
The Earth's shadow will be seen as blue against the pink of
the sunlit smog above it. And as the Earth turns, and the Sun
seems to sink farther and farther below the horizon, the blue
shadow of the Earth will appear to climb higher and higher
through the pink of the sunlit smog. And if you ever have the
opportunity to see this from some thirty-five thousand feet
up in an airplane flying west across the continent, you'll
see how spectacular the colors can be.