Thermal imaging, also called thermography or thermal video, is the means by which humans may see in the infrared portion of the spectrum. Since every object gives off some amount of thermal radiation, thermal imaging is ideal for observing a scene in conditions of extreme darkness or when obscured by smoke, fog, rain, or snow. Some types of night vision use thermal imaging, and thermal imaging is considered the best form of night vision, as it can reveal objects in the blackest of nights. Thermal imaging is used widely in security, the military, navigation, surveillance, firefighting, industry, medicine, and science.
The main tool for thermal imaging is the thermographic camera, which is similar in appearance and operation to a conventional camcorder. Thermal cameras pick up electromagnetic waves with a wavelength between roughly 0.9 and 14 micrometers. In contrast, electromagnetic waves in the visible portion of the spectrum have a wavelength between about 380 to 750 nanometers, significantly shorter than infrared. Though humans are not biologically capable of seeing infrared light unaided, some animals can, notably rattlesnakes and other pit vipers, which have a well-developed pair of organs for the task. Using these organs, rattlesnakes can accurately strike at an object, with their sight and smell cut off, just 0.2 degrees C higher in temperature than its background.
To make thermal imaging easier for humans to interpret, thermal cameras often use false color in their displays, ranging from white for the hottest areas to purple and black for the coldest. The hotter an object is, the more thermal waves it emits. Some of the hottest known objects are stars, and astronomers can infer an enormous amount of information about a star with little else than the electromagnetic energy it emits and its mass. Scientists also use thermal imaging to study how animals emit heat. For instance, polar bears are practically invisible in infrared photography, excepting only their nose, as their bodies have adapted to retain heat in the extreme cold.