I do not know how to build a "sky-detector"
Get a camera, or use the two you were born with.
I still am oblivious as to whether my belief is true or not.
I guess the first step is that you have to want to test your belief. :)
To beg the question (which I think I know the answer to), in this context, how do I trust a camera, or my eyes, to give me a true result?
Let's say that I believe that the sky is green.
1) How can I know whether this belief is true?
2) How can I assign a probability to it to test its degree of truthfulness?
3) How can I update this belief?
Thank you.