• Question: Why is the sunset red?

    Asked by tahmin11 to Joel, Kristian, Tim, Venus, Zachary on 15 Nov 2013.
    • Photo: Tim Hollowood

      Tim Hollowood answered on 15 Nov 2013:

      nice question. The atmosphere affects the way that light travels through it. It’s a bit like a block of glass or what you see when you look into a swimming pool. It’s an effect called refraction. Now red light gets bent the most so that when the sun goes down behind the horizon you can still see the red light because it gets bent. Hence red sun sets.

    • Photo: Zachary Williamson

      Zachary Williamson answered on 15 Nov 2013:

      During a sunset, the Sun is very low on the horizon, and so the Sun’s light has to travel through a relatively large amount of our planet’s atmosphere before reaching your eyes.

      As this light travels through our atmosphere, it bumps into the atoms that make up our atmosphere. Short wavelengths of light are greatly affected by this, compared with long wavelengths. To see this, imagine a bouncy ball (small, blue light) hitting a ball of similar size (an atom in our atmosphere); it’s going to bounce off at some random angle. But if you throw a football (large, red light) into a bouncy ball it’s going to plow on through like nothing happened.

      So, by the time the light has reached your eyes, all the non-red sunlight has been scattered away by the atmosphere. And voila, you have your red sunset.

    • Photo: Kristian Harder

      Kristian Harder answered on 15 Nov 2013:

      Ok, the main thing is that blue light scatters more than red light. Yellow and green are in between.

      During the day, the blue light gets scattered all over the place. Yellow and red get pretty much straight through. That’s why the sky lights up in blue from the light scattered around, whereas the sun appears yellow (with some red, but there is simply a lot more yellow than red coming from the sun).

      But when the sun sets, the light has to pass much more distance through the atmosphere, due to the shallow angle it is going through it with. That means the yellow and red also get scattered quite a bit, making the sky around the setting sun appear a lot more yellowish/reddish. (There is more yellow and red than blue light from the sun, which is why you see mostly the yellow and red parts).
      The red part is really the one that gets scattered least, so the more light gets scattered around in the evening, the more the sun appears red.

    • Photo: Joel Goldstein

      Joel Goldstein answered on 18 Nov 2013:

      Since the others have answered this question well, I’ll just add the fact that the saying “red sky at night, shepherd’s delight” comes from the fact that the sun sets in the west, which is the direction of the prevailing winds. If you can see a nice red sunset that means that there are few clouds to the west, which is the direction the weather is likely to come from and so tomorrow will probably be good weather.

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