How does math relate to being an astronomer?

Answer 1

Because being an astronomer you need to describe the positions of things in the sky. That needs numbers. Then you need to explain why things move Because the planets move among the stars in a fairly strange way, that needs really complicated mathematics. It took over a thousand years before Johannes Kepler used math to discover the shape of the planets' orbits, and then Isaac newton used more math to explain exactly why the orbits are that shape.

Many more things, like the lives of stars, are explained by chemistry and physics, and they both use a lot of math as well.