Eli5: how do thermal cameras capture heat without any physical contact

Question

Eli5: how do thermal cameras capture heat without any physical contact

In: 4

Answer 1

Thermal radiation. Every object thats abow 0K emits light. Higher the temperature the higher frequency light it emits. If the object doesn’t emit light using other methods like a star or a laser based on its thermal radiation you know its temperature. For instance things at room temperature emit in the infrared range. But lets grab some iron and heat it up. As its reaches 1000°C or so it starts to visibly glow red. Red is the lowest visible frequency and as it gets hotter it produces a yellowish glow.