- Liquid crystal sheet (available at museum, nature stores,
and science supply catalogs)
- Table top
1. Have a student touch his or her fingertips on a
table top for 30 seconds. Make sure the student has warm hands.
2. 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 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 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.
This activity uses a liquid crystal detector that senses
heat. Also known as cholesteric liquid crystals, the liquid inside
the sheet exhibits dramatic changes in colors when exposed to slight differences
in temperature within a range of 25 to 32 degrees Celsius. When the student
placed his or her fingers on the table top, heat from the fingertips transferred
to the table's surface. The liquid crystal sheet detects the slight heat
remaining after the student's hand is removed. A visible image of the placement
of the fingertips emerges on the sheet. In the case of an infrared telescope
in space, the energy is detected directly by instruments sensitive to infrared
radiation. Usually, the data is recorded on computers and transmitted to
earth as a radio signal. Ground-based computers reassemble the image.
- How was infrared radiation discovered?
- Learn about cholesteric liquid crystals. An Austrian
botanist, Freidrich Reinitfer, discovered them in 1838.
This Activity is from "Space-Based Astronomy: A Teacher's
Guide With Activities"
Originally published by NASA, August 1994.