
Provide a detailed explanation of why the sky appears blue during the day. Your response should contain at least 3 paragraphs separated by markdown dividers: ***. Highlight at least 2 sections in your answer with markdown, i.e., *highlighted section*. Include keywords *Rayleigh scattering*, *atmosphere*, *sunlight* in the response. At the end of your response, please explicitly add a postscript starting with P.P.S.

user