ABSTRACT
Figure 2.1 can serve as a pleasant point of departure and a stimulant for important questions. In a painting by Prince Eugen of Sweden called The Cloud, solar light is shown reected from a cloud on an otherwise blue sky over a pastoral landscape outside Stockholm, Sweden, in the late 1800s [1]. As scientists we may ask how much of the incident solar light goes through the atmosphere if there are clouds and if there are no clouds? And what part of this solar radiation can our eyes sense? And why do clouds temper the climate and make it less hot at midday and less cold at midnight? These are very important questions! Answering them will in fact enable us to engineer material properties and make the most of the natural ows of energy that occur in the environment. This is what the present chapter is about.
