Why the Sky Appears Blue

Stefan Kim of SciShow explains why the sky appears blue to human eyes due to Rayleigh Scattering, the scattering of light by particles that are much smaller than the wavelength of radiation.

Here's a second component to Rayleigh scattering: shorter wavelengths of light scatter a lot better.So blue light has a much easier time getting into our eyeballs when we look up during the day. but depending on what else is in the sky, another kind of scattering may dictate the final color.

The blue of the sky comes from Mars' atmosphere and the ozone absorbing other colors.

There's a ton of dust floating around. And those dust molecules are super good at absorbing blue light. ...the deep, rich shade of blue we now see at twilight actually comes from ozone absorbing yellow, orange, and red light, leaving blues and purples behind. It's kind of like the opposite of what's going on on Mars.