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, place it where the fingertips touched the table. Observe what happens over the next several seconds.
Infrared telescopes have a detector sensitive to infrared light.
The telescope is placed as high up in the atmosphere as possible on a mountain top, in an aircraft or balloon, or flown in space because water vapor in the atmosphere absorbs some of the infrared radiation from space. 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 the surroundings will create lots of extra infrared signals that interfere with the real signal from space.