system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5 : How does a Thermal Camera work and know the temperature by just seeing the object ?

 I am fascinated by how a Thermal Camera works. It is used for many scientific applications too like measuring a Hot iron rod. As a significant number of people rely on it, I believe it is accurate. How does it make sure what temperature a body is at by just looking at it ? Does the object emit different kind of waves when the degree of temperature is different?
gpt
Yes, all objects emit electromagnetic radiation (waves). Sufficiently hot objects - like the Sun, or a hot iron - emit visible light. Colder objects - like human bodies - emit infrared light, which is a longer wavelength then visible light but still the same kind of physical phenomena. The hotter the object is, the shorter is the wavelength of the electromagnetic radiation it emits. So an infrared camera can translate the wavelengths of infrared radiation it’s seeing into the surface temperature of the object emitting that radiation.

Edit: the Sun and a hot iron actually still emit infrared light along with visible light too.