Something could only appear to be similar to the Sun. We have to trust in observation at some level for all of those experiments to be valid, basically, which means first believing that you're conscious and second believing that you can experience reality and so on from there.

You can never really disprove that some malicious entity is just making you think you're seeing the stars and talking to people, if you want to go back to philosophy about it. There's a bit of assumed faith