Why is the sky blue?

[sandrab]

Dear Sir, How can we ask this question "Why is the sky blue?" in measurable terms? What can we properly measure and how do we properly record the results? My fifth grader came up with this topic, but we are having trouble making it measurable to go with the steps of the scientific method. We are not sure about it. Please help. Thank you. We will be staying up to redo or complete the project. We asked the question, "Does more particles in the air cause the sky to be bluer or redder." We did the sky in a bottle experiment with water, milk, a 2 liter container, and a flashlight. We added 2,4,6,8,and 10 centemeters of milk to the 4 cups of water. We need some advice if this is correct or if there is a better way to handle this topic. We appreciate your time. Sincerely Yours, Concerned parent and Greg

[barretttomlinson]

Hi,

Here is a Science Buddies project that measures turbidity and light scattering, and relates it to color of the sky:

https://www.sciencebuddies.org/science- ... p054.shtml

Here is an explanation of why the sky is blue:

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

Here are explanations of Rayleigh scattering:

http://en.wikipedia.org/wiki/Rayleigh_scattering

http://hyperphysics.phy-astr.gsu.edu/hb ... lusky.html

So the bottom line is that the blue light is scattered more to right angles to the direction of the incident light and its intensity is proportional to the number particles or molecules the incident light strikes (ie the concentration of scattering particles). So you want to measure intensity of scattered light at right angles to the incident light beam versus the concentration of scattering particles, keeping particle size constant.
Another approach is to measure intensity of scattered light by wavelength as a function of angle to the incident light beam keeping the scattering particle concentration constant. You might use red and blue filters on your light meter and measure the angular distribution of light intensity.

I hope this helps.

Good luck on the project,

Barrett L Tomlinson