• Question: Whyy iiS Thee Skyy Bluee, Thee Grass Green Nd Cloudsz Whiitee

    Asked by stephaniiee12 to Daniel, Jon, Louise, Sharon, Zoe on 18 Jun 2010 in Categories: .
    • Photo: Zoe Duck

      Zoe Duck answered on 18 Jun 2010:

      The sky is blue because the molecules in the air scatter blue light better than the other colours of light from the sun.

      Grass is green because it contains cholorphyll, a molecule which used the sun’s light to produce food for the plant. It uses every colour of the sun’s light except green, which is reflected back to our eyes.

      Clouds are white because they reflect all the colours of light back to our eye which then percieves this is white

    • Photo: Louise Dash

      Louise Dash answered on 18 Jun 2010:

      Hi Stephaniiee!

      We already answered “Why is the sky blue” here: /neonj10-zone/2010/06/why-is-the-sky-blue

      The clouds are white, because they consist of water droplets that are much bigger than the wavelength of visible light, so they scatter all colours of light evenly – and a mix of all colours of light is white. When there’s a lot of water in the cloud, it’s denser and so the light can’t get through it as easily – so it looks grey instead of white, and you know it’s going to rain!

      Grass (and the leaves of other plants) is green because of a pigment called chlorophyll. This is a fascinating molecule which allows the plant to get its energy from sunlight, and change carbon dioxide in our atmosphere into oxygen – without it we would not be able to exist! Lots of physicists are trying to work out exactly how it does this so we could use artificial photosynthesis as solar panels to create energy, if we could do that it would be very exciting!

    • Photo: Jon Copley

      Jon Copley answered on 18 Jun 2010:

      Sky blue: the first thing to notice is that the sky only looks blue during the daytime. Sunlight is made up of all the different colours of the rainbow, and each colour of light has its own “wavelength”. Blue light has a shorter wavelength than other colours such as red, yellow and green. This means it can be scattered by molecules of gas in our atmosphere. But only the blue light gets scattered, because the molecules of gas are too small to scatter other the colours that have longer wavelenghts. So the blue light coming from the Sun gets spread all over the sky, making it look blue during daytime. But at night, the light from the Moon and stars is too faint for their blue wavelength light to get spread all over the sky, so then the sky is dark.

      Clouds white: the water droplets and ice crystals in clouds are large enough to scatter the wavelengths of all the colours in sunlight – and when you have all the colours together in light, they make it appear white. But not all clouds are white – sometimes they look grey. That’s happens if the cloud is big (so it casts a shadow over the bottom of the cloud, which is the bit we see), or if there are lots of clouds in the sky. Both usually mean that it’s probably going to rain when the clouds appear grey…

      Grass green: like most other plants, grass contains a pigment called chlorophyll. Chlorophyll absorbs the blue light and red light in sunlight, but reflects the green light – so grass looks green. But if you took some grass into a dark room and just shone a red light on it, it wouldn’t look green – it would just look dark-coloured.

    • Photo: Sharon Sneddon

      Sharon Sneddon answered on 18 Jun 2010:

      White light from the sun consists of all the colors of the rainbow. Since light travels as waves of different lengths, each color has its very own unique wavelength.
      Sunlight reaches Earth’s atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth’s atmosphere. Blue is scattered more than other colors because it travels as shorter, smaller waves. This is why we see a blue sky most of the time.

      In much the same way as why skies are blue, clouds are white because their water droplets or ice crystals are large enough to scatter the light of the seven wavelengths (red, orange, yellow, green, blue, indigo, and violet), which combine to produce white light. Clouds will appear dark or gray when either they are in another clouds shadow or the top of a cloud casts a shadow upon its own base.

      The darkness of a cloud also depends on the background sky. A cloud will look darker when it is surrounded by a bright sky and lighter when it is in front of darker ones. Not always will a dark cloud mean rain.

      More often, the reason we experience dark rainy days is because clouds are blocking the sunlight. Some of the whitest, most pure light can be observed when dark clouds “break apart” and sunlight filters through.

      Grass is green because most species of grass produce a bright pigment called chlorophyll. Chorophyll absorbs blue light (high energy, short wavelengths) and red light (low energy, longer wavelengths) well, but mostly reflects green light, which accounts for grass color.

      But chlorophyll isn’t just for eye candy. It also figures importantly in the process of photosynthesis, by which plants convert an inorganic material (light) into a useable, organic one (sugar). Chlorophyll molecules absorb of light and transfer the energy to special molecules that can, when stimulated, fire off an electron that causes chemical changes in the plant. Further processes turn the chemical energy into sugar.

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