Discuss the below:
a. The internal structure of the Sun and how astronomers learn about the Sun's interior (JUST EXPLAIN WHY & HOW)
b. The Sun is a star. Briefly outline the evolution of a star and where the Sun is in its life cycle.(JUST EXPLAIN WHY & HOW)
Take a "how" and "why" approach (science) rather than a series of unrelated facts (not science). Please provide references.