What are you calculating when you measure the disorder of a system?

Entropy

Explanation:

Entropy is the measure of degree of randomness or disorder.

The systems which have more randomness or disorder of particles have more value of entropy and the system with more ordered arrangement of particles will have less entropy.

Solids with more ordered arrangement of atoms have less entropy and gases with random movement of molecules have more entropy.

blue light is scattered in different directions by the tiny molecules of air. blue is scattered more than other colours because it has a shorter distance to travel which results in smaller waves. this is why we see a blue sky most of the time.