nature & science

Rainbow


(picture: http://photography.nationalgeographic.com)

A rainbow is caused by sunlight that reflects in raindrops. So obviously you can only see a rainbow when it rains and the sun shines.  Raindrops  fall in free fall from the sky and have a round shape due to their surface tension. Sunlight is visible light and consists of different collars. Each of this collars are waves whit a different frequency.  These different frequencies break in a different angle when passing through the raindrop. So the visible light is split into collars. These are the collars you see when looking at a rainbow; red, orange, yellow, green, blue, indigo and violet. In which angle the light breaks, depends on a couple of things such as the refraction index of the water and the size of the raindrops.

You can see a rainbow only when the sun is behind you. We can only see the broken light in an angle of 42 degrees. That's why we see half a circle. 42 degrees is the angle between ingoing and the outgoing sunlight in each of the raindrops which contribute to the rainbow.
Sometimes you see a second or even third bow. They are caused by reflection of the sunlight in the raindrops. Then you see the collars reversed.

(source I used to make this text: Wikipedia)

The northern lights 

(source of the picture: http://www.heel.al/post/noorderlicht/5)

The northern lights (aurora borealis)

You can see the northern lights on the arctic. You can see it best in winter.

There are also southern lights (aurora australis) on the antarctic.

 
There is a connection between the northern lights and sunspots. When there's an explosion on the surface of the sun, large amounts of charged particles are released in the universe.

This stream of highly energetic particles is deflected by the magnetic field of the earth. These deflected particles penetrate the atmophere near the artic and antartic with a large velocity. In the atmospere, the energy of the sunparticles is transferred on the oxygen and nitrogen atoms by collisions. Eventually the energy is released and emitted in the form of colorful aurora.

I think it would be really awesome to see this in real life! :-)

 

(source I used to make this text: Wikipedia)