: On Earth, the sky appears blue due to Rayleigh scattering , where nitrogen and oxygen molecules in the atmosphere scatter shorter blue light waves more effectively than other colors. Interestingly, NASA has also detected blue skies on Pluto caused by soot-like "tholin" particles.
: Many observers notice the sky appears bluer in autumn. This is due to lower humidity and fewer pollutants like dust or pollen, which allows for cleaner scattering. Blue Skies
: The United Nations observes the International Day of Clean Air for blue skies every September 7 to raise awareness about air pollution. Research & Innovation : On Earth, the sky appears blue due