system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is air invisible?
gpt
Humans eyes only react to a pretty narrow band of radiation (visible light), on the whole electromagnetic spectrum its pretty small.

Different wavelengths of light pass through or get stopped by different materials (the radio waves for your cellphone can get through the walls of your room but sunlight can’t). It has to do with the density and electron structure of molecules/atoms, they like to absorb certain wavelengths, reflect others, and just ignore the rest.

So the air ignores visible light, it passes straight through and that is what makes it invisible to us, no light bounces off it that our eyes can see.

This phenomena is actually the basis for global warming. CO2 ignores visible light and ultraviolet light from the sun, but loves infrared light from the earth. So it lets energy from the sun go through, but traps/absorbs heat escaping from the earth, because thats a wavelength that it likes.