What are some ways astronomers use visible light?

Question

 What are some ways astronomers use visible light part of the electromagnetic spectrum?

Answer 1

I will give you one example:

 

Astronomers can determine the composition of a star by examining its spectrum.  The various chemical elements emit radiation at specific wavelengths, which show up as lines in a spectrum.  By detecting these lines, they can know the element is present in the star.  By comparing the brightness of different lines, they can determine relative abundances of the elements.