image credit: NASA/IPAC; image source; no larger image available
Cooling of the Human Body
These faces were photographed in infrared light.
-- Notice how different parts of the face are brighter or dimmer, and compare the two noses.
-- Infrared images are sensitive to the temperature of different parts of the face because the heat radiation emitted per second varies as the fourth power of the temperature, so a small difference in temperature makes a big difference in the brightness of the image.
-- For more on this temperature dependence, see Hyperphysics' Cooling of the Human Body. For related images, see Caltech's Our IR World Gallery
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Exploratorium Science Snacks: Hot Spot
In this Exploratorium activity, you focus a beam of invisible heat radiation on your skin with a large parabolic mirror and then use your skin as a radiation detector. To learn more about this activity, visit Exploratorium Science Snacks: Hot Spot, and while you're there, notice the image of the radiant heater made by the mirror in visible light.