system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Why is air invisible to infrared cameras? Why isn't the entire image the temperature of the air? Also, what is the relationship between infrared light and heat?
gpt
Infrared light is just like any other color of light, its just below the level that we can see. Heat is a measure of how much motion particles have. We know that hot things give off light- this is why metal glows when it gets hot, or why the sun is bright. Things that are not quite that hot also give off light, it just doesn't have enough energy to be of a color that we can see. Infrared cameras take a look at that light, and then shift the frequency to be a color we can see.

Just like all other light, infrared can only be detected when it bounces off of something. Air does a really bad job of bouncing light (of any color) back at us, so cameras don't pick it up well.