To experiment with one method of detecting infrared radiation. Have a student touch his or her fingertips on a table top for 30 seconds. Make sure the student has warm hands. While handling the liquid crystal sheet only by its edges, put it on the spot where the fingertips touched the table. Observe what happens over the next several seconds.
Infrared telescopes have a detector sensitive to infrared light.
The human eye is not sensitive to infrared light, but our bodies are. We sense infrared radiation as heat. Because of this association with heat, telescopes and infrared detectors must be kept as cool as possible. Any heat from their surroundings will create extra infrared signals that interfere with the real signal from space. Astronomers use cryogens such as liquid nitrogen, liquid helium, or dry ice to cool infrared instruments.