You could make an argument for Lucian's "A True Story" from the second century.
You could make an argument for Lucian's "A True Story" from the second century.
Perhaps these questions don't really mean much. There is also the Bible which at least starts out as science fiction before getting really crazy.
The bible doesn't have outer space in it though.
Revelation has a city in Heaven which is outer space if you squint
As I understand it, the argument for Shelley being one of the earliest practitioners of sci-fi is that you can't have science fiction before you have proper science to put in it, which is obviously a fairly modern methodology. Genre aficianados might say Shelley pioniere 'hard' SF.