• Question: why is the sky light blue straight above you, but darker when you look at the horizon?

    Asked by jesusjones to Andrew, Ben, Beth, Heather, Louisa on 22 Jun 2010 in Categories: . This question was also asked by adamepi8316.
    • Photo: Heather McKee

      Heather McKee answered on 18 Jun 2010:


      the sky is blue due to the scattering of light

      The light from the Sun looks white. But it is really made up of all the colors of the rainbow and it travels in waves.
      All light waves travel in a straight line unless something gets in the way. If random particals(water or dust) or something gets in the way it can either reflect it (like a mirror), bend it (like a prism), or scatter it (like molecules of the gases in the atmosphere).

      When the sunlight reaches earth’s atmosphere it hits the gases (nitogen, oxygen etc.) in the in the air and this causes the light to scatter in all directions (because the gases and paticles in the air have blocked the light waves!). Blue is scattered more than other colors because it travels as shorter, smaller waves…so more blue waves reach the gases and particles to be scattered! This is why we see a blue sky most of the time.
      As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes. As such the blue light on the horizon appears darker as less light is scattered here, the light straight above you is subject to scattering via the sun and therefore lighter however the further it is from the sun (i.e on the horizon) the darker it becomes.

      heres a question -why is the sky black in space?

    • Photo: Andrew McKinley

      Andrew McKinley answered on 19 Jun 2010:


      What makes the sky blue is the same thing that makes a sunset red. When light hits particles, it scatters off them – think of a shaft of sunlight through your curtains – it scatters off dust particles and you can see the shaft of light. Weird things happen though when those particles get smaller. The smaller the particles get, then they start to affect different colours of light differently. Once the particles are the same sort of size as the wavelength of light, the colours scatter differently. Blue light has the most energy, so is scattered the most, whereas the red light isn’t affected as much.

      Straight above us, we will see scattered light, so the sky appears blue. In the evening, when the sunlight passes through a lot of atmosphere, all the blue light from the sun has been scattered away, just leaving the red and yellow shades, hence the sunset looks red.
      Most of the blue light is scattered from straight above, so the blue looks better there than it does around the horizon where the light is not scattering at a good enough angle to see the blue.

    • Photo: Louisa Chard

      Louisa Chard answered on 22 Jun 2010:


      Hiya

      I don’t knowthe full answer for this. I think though that if you look out from on a plane, you see that the horison is lighter than the sky above you and it has something to do with the way the sunlight refracts through the atmosphere. Ben por Andrew would know more about this I think. Sorry!

Comments