Example 1.3 in the textbook

[Leslie Contreras 1D]

We were only shown Weins law but will we use Stefan-Boltzmann
law Total intensity=constant xT^4
When will this concept come up? Can someone explain to me why T^4

[jadam_1E]

I think there will be some concept based questions on stefan boltzmann law, at the very least.

For the second part of your question, T^4 because it was found that the intensity is not simply directly proportional to T, but it is proportional to T^4 (the temperature to the 4th power). The unit used for temperature in the stefan boltzmann law is generally the Kelvin.

[Steve H]

An example question: What equation helps astronomers determine a star's temperature, size, composition, and age of a star? Because this concept is new to us and very complex, I am sure there will not be many questions about this on the final/midterm.

[Chem_Mod]

There is a physical reason why it should be T^4 which becomes apparent as you start deriving it. However, I will not explain it here since you need to understand statistical mechanics, which you start encountering in upper division physics courses.