• Question: Why is the sky blue? ;D

    Asked by adaammm to Andrew, Ash, Gem, Paige, SJ on 29 Jun 2012.
    • Photo: SarahJayne Boulton

      SarahJayne Boulton answered on 29 Jun 2012:


      It’s all to do with angles!!

      During the daytime, blue light is scattered more effectively by molecules in the air than other colours with short wavelengths like yellow and blue, meaning the blue light bounces down to us and the red light travels through the atmosphere to other parts of the globe.

      As the sun sets and rises, the angle of the sun in comparison to us means the reds, pinks and oranges of the suns light are scattered towards us, so we see those colours just at the beginning and end of the day, then blue in the middle!

    • Photo: Paige Brown

      Paige Brown answered on 29 Jun 2012:


      I think we answered this one over chat!!

      The sky is blue to due Rayleigh scattering! Very small particles in the sky cause light to bounce off of them, or scatter off of them. But these particles don’t scatter ALL light the same… some light is scattered to a larger extent than others. For example, longer wavelengths of light, like yellow and red, are no as easily scattered as smaller or shorter wavelengths such as blue. SOOO… blue light is scattered and bounced around so much in the sky, vs. being absorbed, that blue is the color you see when you look into the sky! At sunset, as light has to travel through more atmosphere to reach your eyes, the red light is more directly traveling to your eyes. The blue light is scattered away, so you can see some the the yellows and reds that you can’t normally see because the blue scattered light overpowers them during the normal day!!!

      Crazy right?! As Andrew told us, there is an experiment you can do to see this effect: Put water in a glass and add a bit of milk a little at a time, looking through the glass at a light. If you look through the top of the glass you will see blueish tint, but if you look through the bottom you may see red!!

      Clouds are white because the larger particles scatter ALL light. You know what all the colors of the color spectrum make when added together right? White!

      More about scattering the in sky: http://en.wikipedia.org/wiki/Rayleigh_scattering

      http://www.optics.rochester.edu/workgroups/berger/EDay/Optics%20demonstrations%20for%20the%20classroom.pdf

      http://www.sciencemadesimple.com/sky_blue.html

    • Photo: Andrew Thomas

      Andrew Thomas answered on 30 Jun 2012:


      SJ and Paige have answered this question and I only have a couple of things to add. The reason that we get red sky in the evening is actually because when the sun is lower down in the sky it has to pass through more of the atmosphere so more red light is scattered to us. You may have notices that in cities we get much redder skies than in the countryside because there are more particles from pollution in the atmosphere.

      In the milk experiment (actually dettol or something like that works much better) as you add more and more to your water the colour will change from a bluish grey to milky pink if you hold it up to a window or white light.

      Better still hold a bright torch (battery powered not mains!!) under the glass and add the dettol drop by drop and stir it up. From the side you should see the water looks bluish when you don’t have much of your scatterer in there and if you look from the top of the glass, the torch light will look yellow, like the sun at mid day. As you add more of the dettol then the water gets more pinky from the side and the torch should look deep red from the top

    • Photo: Ashley Cadby

      Ashley Cadby answered on 5 Jul 2012:


      I think this might be cheating but here is Paige’s answer (don’t tell her I copied it ;-))
      I think we answered this one over chat!!

      The sky is blue to due Rayleigh scattering! Very small particles in the sky cause light to bounce off of them, or scatter off of them. But these particles don’t scatter ALL light the same… some light is scattered to a larger extent than others. For example, longer wavelengths of light, like yellow and red, are no as easily scattered as smaller or shorter wavelengths such as blue. SOOO… blue light is scattered and bounced around so much in the sky, vs. being absorbed, that blue is the color you see when you look into the sky! At sunset, as light has to travel through more atmosphere to reach your eyes, the red light is more directly traveling to your eyes. The blue light is scattered away, so you can see some the the yellows and reds that you can’t normally see because the blue scattered light overpowers them during the normal day!!!

      Crazy right?! As Andrew told us, there is an experiment you can do to see this effect: Put water in a glass and add a bit of milk a little at a time, looking through the glass at a light. If you look through the top of the glass you will see blueish tint, but if you look through the bottom you may see red!!

      Clouds are white because the larger particles scatter ALL light. You know what all the colors of the color spectrum make when added together right? White!

      More about scattering the in sky: http://en.wikipedia.org/wiki/Rayleigh_scattering

      http://www.optics.rochester.edu/workgroups/berger/EDay/Optics%20demonstrations%20for%20the%20classroom.pdf

      http://www.sciencemadesimple.com/sky_blue.html

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