DIY Sunset

Have you ever wondered why the sky is blue at noon and orange in the evening?

To understand this, we will create a sunset using materials found around the house. It's a simple yet informative project.

For those who would like to know more in depth, it is the Rayleigh scattering.

1. It results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle, therefore, becomes a small radiating dipole whose radiation we see as scattered light. The particles may be individual atoms or molecules; it can occur when light travels through transparent solids and liquids, but is most prominently seen in gases.

1. Fish tank or square glass bowl
2. Glass of milk
3. Syringe
4. Spoon
5. 1 liter water
6. Flashlight
7. White paper
8. Polarizer (if you don't have one you can still perform the experiment)

Fill the container with a liter of water to a height that exceeds the width of the lantern since the light must pass through the liquid.

Using the syringe, we pour a few milliliters of milk into the tank. Then, using a spoon, we mix until the mixture is uniform.

At first glance, it is clear that the liquid in the tank has turned white due to the addition of milk. At this point, light arriving and passing through this medium interacts with the molecules in the solution.

We place the polarizer in front of the tank. By rotating it, we observe whether the object lets light pass through or blocks it. This is because the molecules inside the liquid change the polarization of the light that reaches them.

We position the flashlight at one end of the tank so that the emitted light passes through the aqueous medium and crosses it entirely until it reaches the white paper placed at the other end, which functions as a screen.

We can observe that the light entering the fish tank has a bluish-white hue. As it moves further into the medium, however, the light becomes orange.

When we look at the screen, we see an image reminiscent of a sunset.

We see the sky as blue because the light components of that color are strongly scattered in the atmosphere (a process known as Rayleigh scattering). In the evening, we see an orange tone because the sun's rays travel a much greater distance through denser areas of the atmosphere. Therefore, the light that reaches our eyes has lost most of its blue components. Yellow, orange, and red tones therefore predominate. In other words, the longer wavelengths of light predominate.