WHY ARE SUNSETS RED? ARE THEY ONLY ROMANTIC THIS WAY?
In our article about the blue sky of Earth
Read here
we saw that sunlight is white. But when that white light passes through a prism, it splits into its spectrum.
Because of selective scattering by Earth’s atmosphere, this “white” light turns into what we see above us: a blue sky during the day, when the Sun is high.
But when the Sun is setting, its light travels through a much longer distance within Earth’s atmosphere. The result? Beautiful, fiery-red sunsets. As we’ve said before, blue light scatters more, so only red light reaches our eyes.
So, the blue sky and the red sunset are actually evidence that our planet has an atmosphere.
This interaction of light with the atmosphere also creates other phenomena.
For example:
Did you see the red Moon on March 13–14, 2025? Why did that happen?
Someone might ask:
If we have a full moon once a month, why is it bright red so rarely?
Could it be for the same reason we see the morning sky blue and sunsets red?
In the next diagram, we see a lunar eclipse. In such an eclipse, it’s clear that the Moon sometimes enters the Earth’s shadow (umbra).
When the Moon is in that shadow, the blue sunlight is scattered in all directions, leaving only the red light to reach us.
The result is images like the one below.
For many ancient cultures, this red Moon was frightening. The Inca, for example, believed that a jaguar had bitten a piece out of the Moon.
Folk wisdom holds many such fascinating stories — perhaps worth exploring more deeply sometime.