Question

why do you classify the sun as a star

Answer 1

The Sun happens to fit that criteria, so it is classified as a star. ... It's quite simple as like all other stars, it is a giant ball of hydrogen and helium gas where continuously nuclear fusion is taking place. The sun seems a lot brighter than the stars because we're rightnext door to it.

Answer 2

The sun undergoes nuclear fusion within its core, which is something stars do and planets don't do. Not only is the sun a star, but it's actually the closest star to Earth and vital for life here. Our sun appears to be yellow from our viewpoint here on Earth, but it is actually white. Hence we classify the sun as a star.