Question

What does romeo mean by "Then I defy you, stars?"

Answer 1

Then I defy you, stars! In Act V scene I Romeo has just found out that Juliet is dead. He is beside himself with grief and he curses "I defy you, stars," which means he denies fate. He denies fate's hold on him and he then plans to kill himself.

Answer 2

Romeo has found Juliet "dead". He is besides himself with grief and he curses "Then I defy you, stars!", which means he denies fate. He's denies fate's hold to him and that is when he decides to kill himself after he sees the love of his heart dead since he planned to marry Juliet. 

Hope this helped - Maria S.