Welcome to the newest edition of The Why. “Why does the sun turn red at sunset?” you ask? Good question. (Besides, it beats answering the question: “Why do some people make an issue of Columbus Day when all federal employees still get it off as a paid holiday and half of the country still acknowledges it as a holiday despite all the PC attitudes?”)
Wow. That question itself said plenty about Columbus Day. So for now, let’s consider our question of the day: Why does the sun turn red at sunset?
For those of you who never get out of the house, when the sun sets, it appears to get redder as it gets closer to the horizon. As sources such as EarthSky note: Sometimes one can even see “a gradation of color a across the sun’s surface.” The question is why does this occur?
Science teaches us that if you were an astronaut standing on the moon and saw a sunset that the sun would look white. Why? The moon has no atmosphere.
Earth, on the other hand, has an atmosphere. Science also teaches us that white light—such as sunlight—is actually made up of all colors.
If you have already perused our piece on “Why is the sky blue?”, then you know that molecules in Earth’s atmosphere make the light scatter. So just as the atmosphere scatters the blue part of white sunlight to make the sky blue, similarly it causes the sun to appear red or reddish when it is close to the horizon.
As one looks toward the horizon, he/she is actually “looking through more atmosphere than when you look overhead.” As the sun begins to set in the sky, the light must “travel farther and farther through the atmosphere before” it reaches the human eye because there is “more atmosphere in the direction toward the horizon than overhead.”
The light from the sun meets more air molecules when the sun’s low in the sky than when it is high overhead. Additional blue light is scattered and mainly the red portion of the white sunlight travels to the eyes. This makes the setting sun appear red.
Simply put the sun “turns” red at sunset because when you look toward the horizon, you are looking through significantly more of Earth’s atmosphere than when you are looking overhead.
Why does the sun turn red at sunset? Now you know.
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