This question already has an answer here:
Finn witnesses the destruction of Hosnian Prime and 4 other planets while standing on Takodana. If Takodana is not in the Hosnian system (Wookieepedia doesn't seem to think it is) how can they see the planets so distinctly? Is this just a case of "Star Wars is fantasy, not science" or is there a different explanations? Are the "Western Reaches" just really jam packed with close together systems?