Welcome to Earth - a perfectly sunny planet! Why is it important to understand Earth-Sun Interactions? One quick example is that understanding the Sun helps us determine the best PV panel tilt angle, which depends primarily on your latitude. The optimum tilt increases as you move away from the equator because insolation is more oblique as you move towards the poles. Today, we will learn about how energy from the sun is distributed around the Earth and how that influences the Earth system and increasingly our daily lives. By the end, we will be able to answer the questions: How can we calculate the amount of sunlight across the Earth? Why does the Earth have seasons? Why exactly does the Earth experience glacial cycles?  And how does orbital forcing and anthropogenic radiative forcing compare?