In Greek mythology Venus is Aphrodite, the goddess of love but also of beauty. The ancient civilizations already knew stars and planets at that time and could distinguish them.  The planet probably got this name because it was the brightest planet known in ancient times. But also because the goddess of beauty could shine like a star. In former times there was also a social ideal of women, just like today, and you know how it is @mabdullahch. Shine like a Star and you are the beauty and beauty means love (or also the other way around)...